Synthesis of (E)-oxindolylidene acetate using tandem palladium-catalyzed Heck and alkoxycarbonylation reactions

Abstract

Tandem reactions use consecutive reaction steps to efficiently synthesize compounds of high molecular complexity. This paper presents a tandem Pd-catalyzed Heck and alkoxycarbonylation reaction for the stereoselective synthesis of (E)-oxindolylidene acetates. The mechanism underlying the Pd-catalyzed tandem reaction involves the syn-carbopalladation of ynamides followed by alkoxycarbonylation with CO and alcohol. This method makes it possible to obtain the desired (E)-configuration of oxindolylidene acetates exclusively. We evaluated the scope of the reaction by applying optimal reaction conditions to the facile synthesis of a library of (E)-oxindolylidene acetates. The resulting (E)-oxindolylidene acetates exhibited potent anticancer activities against a variety of human cancer cell lines. The anticancer activities of some (E)-oxindolylidene acetates were even superior to those of known CDK inhibitors indirubin-3′-oxime and roscovitine.

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Introduction

The 3-ylideneoxindole moiety is a skeleton of pharmacological importance, which appears as the core structure in a variety of bioactive molecules exhibiting potent antifungal,¹ anticancer,² and antiviral activities.³ For example, 3-ylideneoxindole is the core structure in biologically active compounds such as sunitinib and hesperadin, which possess the capacity to bind receptor tyrosine kinase (RTK) and Aurora B with high affinity.^4–6 3-Ylideneoxindole also exists in a number of natural indole alkaloids (including neolaugerine,⁷ costinone A, and costinine B⁸) which possess a variety of biological properties.

Tandem reactions are a series of consecutive reactions that provide a highly efficient means of assembling compounds.⁹ The molecular complexity and diversity that can be created using this facile approach is suitable for combinatorial library synthesis as it is able to produce a large number of compounds using a minimum number of steps.¹⁰

The synthesis of a 3-ylideneoxindole moiety has attracted considerable interest among researchers, and impressive advances have already been made in which 3-alkylideneoxindole was used as an important intermediate such as the synthesis of TMC-95A.¹¹ The stereoselective synthesis of various substituted 3-alkylideneoxindoles from a series of ynamides and boronic acids by way of palladium-catalyzed Heck–Suzuki–Miyaura domino reactions has also been reported.¹² The domino reaction, which further expands the utility of ynamides, has been applied in the preparation of natural, biologically active products.

Oxindolylidene acetate is commonly used as a synthetic target due to its interesting biological activities.¹³ Previous successes involving the use of metal-catalyzed tandem reactions led us to consider whether Pd-catalyzed tandem Heck and alkoxycarbonylation reactions of ynamides with carbon monoxide (CO) and alcohols in a single pot could be used to produce oxindolylidene acetate. In the following, we report a concise method for the stereoselective synthesis of (E)-oxindolylidene acetates using the tandem Pd-catalyzed Heck and alkoxycarbonylation reactions of N-substituted propiolamides. The resulting (E)-oxindolylidene acetates exhibited potent anticancer activities against a variety of human cancer cell lines.

Results and discussion

Tandem Pd-catalyzed Heck and alkoxycarbonylation reactions were combined to develop an efficient stereocontrolled method for the synthesis of (E)-oxindolylidene acetates using CO and alcohols in one pot (Chart 1). Tandem Pd-catalyzed Heck–Suzuki–Miyaura domino reactions have previously been used to synthesize 3-alkylideneoxindoles;¹² however, this is the first study to report on the use of tandem metal-catalyzed reactions in the synthesis of oxindolylidene acetates from ynamides. At the outset of our investigation, N-(2-iodophenyl)-N-(4-nitrobenzyl)propiolamide (1a) was selected as the model compound for the evaluation of tandem reactions. We initially evaluated the reaction of N-(2-iodophenyl)-N-(4-nitrobenzyl)propiolamide (1a) and methanol (3 equiv.) under CO at atmospheric pressure and elevated temperatures. The reaction was conducted in the presence of triphenylphosphine (0.5 equiv.) in THF, and Pd(OAc)₂ was used as a catalyst.¹⁴ The desired (E)-oxindolylidene acetate (3a) was obtained at a yield of 23% wherein only the (E)-configuration was found (Table 1, entry 1).

Chart 1 Tandem Pd-catalyzed Heck and alkoxycarbonylation reactions.

Table 1 Optimization of reaction conditions^a

Entry	[Pd]	Ligand	Additive	Solvent	Yield^b (%)
a Reaction conditions: 1.0 equiv. of ynamide 1a (0.05 M in solvent), 3.0 equiv. of CH3OH (except entry 22), 0.1 equiv. of the Pd catalyst, 0.2 equiv. of the ligand, and 3.0 equiv. of the additive for 6 h; temperature was 60 °C and CO pressure was 1 atmosphere. b Yields refer to isolated and purified compounds.
1	Pd(OAc)2	PPh3	—	THF	23
2	Pd(OAc)2	PPh3	K2CO3	THF	12
3	Pd(OAc)2	PPh3	Cs2CO3	THF	34
4	Pd(OAc)2	PPh3	KF	THF	66
5	Pd(OAc)2	PPh3	CsF	THF	64
6	Pd(OAc)2	PPh3	KI	THF	51
7	Pd(OAc)2	—	KF	THF	14
8	Pd(OAc)2	dppp	KF	THF	15
9	Pd(OAc)2	dppe	KF	THF	24
10	Pd(OAc)2	dppe	KI	THF	18
11	Pd(OAc)2	PPh2Me	KF	THF	41
12	Pd(OAc)2	PCy3	KF	THF	21
13	Pd(PPh3)4	—	KF	THF	38
14	Pd(PPh3)2Cl2	—	KF	THF	43
15	Pd2(dba)3	PPh3	KF	THF	36
16	Pd(dppf)Cl2	—	KF	THF	65
17	Pd(OAc)2	PPh3	KF	m-Xylene	19
18	Pd(OAc)2	PPh3	KF	CH3CN	8
19	Pd(OAc)2	PPh3	KF	DME	47
20	Pd(OAc)2	PPh3	KF	1,4-Dioxane	22
21	Pd(OAc)2	PPh3	KF	DMSO	5
22	Pd(OAc)2	PPh3	KF	CH3OH	71

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Notably, additives and phosphine ligands were shown to play important roles in the Pd-catalyzed tandem reaction. In fact, the addition of KF increased the yield from 23% to 66% (Table 1, entry 4); therefore, we subsequently turned our attention to the evaluation of various additives with the aim of further improving the reaction yields (Table 1, entries 2–6). A number of carbonates, such as potassium carbonate and cesium carbonate, were used as additives; however, the resulting yields were lower than the yield achieved using KF (Table 1, entries 2–4). Conversely, using potassium fluoride, cesium fluoride, or potassium iodide as additives resulted in better yields of (E)-oxindolylidene acetate (Table 1, entries 4–6). Phosphine ligands were also shown to exert a strong effect on the yield of the Pd-catalyzed tandem reaction, as the reaction without the phosphine ligand resulted in poor yield (Table 1, entry 7), and the reactions with bulky bidentate ligands (dppp and dppe) or monodentate phosphine ligands (PPh₂Me and PCy₃), provided only slightly better yields than reactions without the addition of ligands (Table 1, entries 8–12). As shown in Table 1, PPh₃ proved to be a more effective ligand for this reaction and others. A variety of palladium catalysts were subsequently used to evaluate the stereoselective synthesis of (E)-oxindolylidene acetate under CO and atmospheric pressure at elevated temperatures. The palladium catalysts Pd(OAc)₂ and Pd(dppf)Cl₂ proved efficient for this tandem reaction; however, other palladium catalysts produced lower yields (Table 1, entries 4 and 13–16).

We further evaluated how a variety of solvents affected this Pd-catalyzed tandem reaction. Among these, methanol and THF provided the best results. In addition, trace quantities of N-substituted dimethyl 2-(2-oxoindolin-3-ylidene)malonate was also observed in this reaction, perhaps due to the presence of trace quantities of oxygen, which may have caused the oxidative alkoxycarbonylation of the terminal alkyne in the first step.¹⁵

After establishing the optimal reaction conditions, we investigated a series of N-substituted propiolamides 1 with various primary, secondary, and aryl alcohols in order to determine the scope of the reaction (Table 2). Alkoxycarbonylation is sensitive to the steric features of alcohols, and we observed that when N-substituted propiolamides 1 and various primary aliphatic alcohols, such as methanol, ethanol, and n-butanol underwent Pd-catalyzed tandem Heck and alkoxycarbonylation reactions the yield was good. Conversely, isopropanol, phenol, and benzyl alcohols were unreactive (Table 2, entries 34–36). In addition, The Pd-catalyzed tandem Heck-alkoxycarbonylation reactions revealed excellent functional group tolerance with benzyl substituents at R¹ bearing electron withdrawing groups at the phenyl ring, such as nitro, methyl ester, trifluoromethyl and cyano resulting in a smooth reaction, resulting in corresponding oxindolylidene acetates 3a, 3f, 3g and 3h in good yields. Benzyl and p-methoxybenzyl in the R¹ position were also well tolerated in the reaction, thereby producing corresponding oxindolylidene acetates 3m and 3b with yields of 64% and 67%, respectively. In addition, substitution at the R¹ position with an isoxazolylmethyl ring, methyl and H, the products 3n, 3t and 3u were obtained exclusively in fair yields. Finally, the reaction conditions were found to be favorable when functional groups 5-methyl, 5-methoxyl, and 5-chloride were substituted at R³ (Table 2, entries 17, 18, 27 and 28), such that the resulting reactions respectively produced corresponding oxindolylidene acetates 3q, 3r, 4e and 4f in good yields.

Table 2 Reaction scope^a

Entry	R^1	R^2	R^3	Product	Yield^b (%)
a Reaction conditions: 1.0 equiv. of ynamides 1 (0.05 M in CH3OH), 0.1 equiv. of the Pd catalyst, 0.2 equiv. of PPh3 and 3.0 equiv. of KF for 6 h; temperature was 60 °C and CO pressure was 1 atmosphere. b Yields refer to isolated and purified compounds, and only the (E)-configuration of oxindolylidene acetate was found. c The yield was negligible.
1	p-NO2-PhCH2	Me	H	3a	71
2	p-MeO-PhCH2	Me	H	3b	67
3	p-F-PhCH2	Me	H	3c	60
4	p-Cl-PhCH2	Me	H	3d	68
5	p-Br-PhCH2	Me	H	3e	64
6	p-CO2Me-PhCH2	Me	H	3f	74
7	p-CF3-PhCH2	Me	H	3g	70
8	p-CN-PhCH2	Me	H	3h	66
9	m-CN-PhCH2	Me	H	3i	51
10	m-Cl-PhCH2	Me	H	3j	58
11	2-Np-CH2	Me	H	3k	59
12	o-Cl-PhCH2	Me	H	3l	57
13	Bn	Me	H	3m	64
14	3-Methyl-5-isoxazolylmethyl	Me	H	3n	55
15	2,6-Cl2-PhCH2	Me	H	3o	59
16	3,4,5-(MeO)3-PhCH2	Me	H	3p	68
17	p-Cl-PhCH2	Me	5-Me	3q	67
18	p-Cl-PhCH2	Me	5-OMe	3r	64
19	(6-Bromobenzo[d][1,3]dioxol-5-yl)CH2	Me	H	3s	54
20	Me	Me	H	3t	61
21	H	Me	H	3u	51
22	p-NO2-PhCH2	Me	5-CF3	3v	45
23	p-NO2-PhCH2	Et	H	4a	62
24	p-Cl-PhCH2	Et	H	4b	59
25	p-Br-PhCH2	Et	H	4c	57
26	3,4,5-(MeO)3-PhCH2	Et	H	4d	64
27	p-Cl-PhCH2	Et	5-Cl	4e	55
28	p-Cl-PhCH2	Et	5-OMe	4f	61
29	Me	Et	H	4g	58
30	m-CN-PhCH2	^nBu	H	5a	57
31	p-CN-PhCH2	^nBu	H	5b	53
32	p-NO2-PhCH2	^nBu	H	5c	55
33	H	Et	H	4h	58
34	p-NO2-PhCH2	^iPr	H		—^c
35	p-NO2-PhCH2	Ph	H		—^c
36	p-NO2-PhCH2	Bn	H		—^c

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One plausible mechanism for the formation of compounds 3–5 is presented in Scheme 1. The formation of the products may initially have followed the Heck reaction mechanism, which involves the syn-carbopalladation of ynamide with a palladium catalyst to form the intermediate A. The resulting products 3–5 were obtained following alkoxycarbonylation of intermediate A treated with CO and alcohols. This mechanism involves a syn migratory insertion of the alkyne into the Ar–Pd bond, followed by the alkoxycarbonylation of CO and alcohols, leading to the only (E)-configuration of oxindolylidene acetate.

Scheme 1

All of the synthesized (E)-oxindolylidene acetates 3–5 obtained via tandem Pd-catalyzed reactions were evaluated for anticancer activities using human NCI-H460 lung cancer cells. We then studied the structure–activity relationships (SARs) in compounds containing various substitutions in the (E)-oxindolylidene acetate scaffold. Specifically, we examined the antiproliferative effects of various R¹ and R² groups on oxindolylidene acetates. Compounds 3d, 3h, and 5b, containing para-substituents on the phenyl ring of the R¹ group, presented slightly better anticancer activity than did compounds 3i, 3j, 3l, and 5a, which contained meta- and ortho-substituents on the phenyl ring of oxindolylidene acetates. Interestingly, compound 3n, containing an isoxazolyl ring, was found to decrease the anticancer activity to below that of compounds with a phenyl ring at R¹. In our evaluation of the anticancer activities of methyl, ethyl, and n-butyl groups at R², the activity of the methyl group was found to be superior to that of ethyl and n-butyl groups, and the order of activity of R² groups against NCI-H460 cancer cells can be described as methyl > ethyl > n-butyl in most examples. However, substitutions at R³ did not have significant effects on anticancer activity (Table 3).

Table 3 In vitro anticancer activities of (E)-oxindolylidene acetate in NCI-H460 cells^a

Compound	IC50 (μM)	Compound	IC50 (μM)
a IC50 values represent the mean ± SD of three determinations. b Reported IC50 = 13.1 μM.
3a	5.2 ± 0.7	3r	3.7 ± 0.1
3b	5.1 ± 0.4	3s	18.8 ± 1.9
3c	6.3 ± 0.3	3t	7.8 ± 1.6
3d	6.8 ± 0.8	3u	5.5 ± 0.4
3e	7.4 ± 0.6	4a	8.7 ± 0.5
3f	4.3 ± 0.3	4b	6.8 ± 0.7
3g	2.0 ± 0.1	4c	8.3 ± 0.5
3h	5.3 ± 0.6	4d	6.2 ± 0.3
3i	8.9 ± 0.7	4e	9.3 ± 0.7
3j	9.6 ± 0.5	4f	7.7 ± 0.8
3k	4.2 ± 0.8	4g	11.8 ± 1.3
3l	6.2 ± 0.6	5a	17.3 ± 1.6
3m	5.1 ± 0.7	5b	14.9 ± 1.9
3n	52.0 ± 3.4	5c	19.2 ± 1.7
3o	4.4 ± 1.5	4h	38.6 ± 3.7
3p	1.2 ± 0.1	Indirubin-3′-oxime	32.6 ± 5.1
3q	3.9 ± 0.4	Roscovitine	11.6 ± 1.9^b

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Further evaluation of anticancer activities was conducted on selected active (E)-oxindolylidene acetates using six different cancer cell lines: human lung adenocarcinoma cell CL 1–5, human epidermoid carcinoma KB, human gastric cancer MKN-45, human breast adenocarcinoma MCF-7, human pancreatic carcinoma MIA Paca-2, and human central nervous system cancer SF-268 (Table 4). Most of the 3-ylideneoxindole acetamides exhibited a broad spectrum of anticancer activity against human cancer cells, with effects even more pronounced than those associated with well-known anticancer drug candidates indirubin-3′-oxime and roscovitine.

Table 4 In vitro anticancer activities of (E)-oxindolylidene acetate against various cancer cell lines^a

Compd	CL 1–5	KB	MKN-45	MCF-7	MIA Paca-2	SF-268
a IC50 values represent the mean ± SD of three determinations. b Reported IC50 = 30.1 μM. c Reported IC50 = 14.7 μM.
3b	4.6 ± 0.5	5.5 ± 1.7	3.4 ± 0.6	27.1 ± 0.5	39.4 ± 2.8	3.7 ± 0.4
3f	5.7 ± 0.6	5.6 ± 0.6	5.0 ± 0.6	8.5 ± 5.1	38.3 ± 2.2	3.9 ± 0.5
3g	5.3 ± 0.2	4.3 ± 0.3	5.1 ± 0.2	8.3 ± 4.5	37.6 ± 2.8	4.4 ± 0.6
3h	7.3 ± 0.3	4.9 ± 0.1	6.4 ± 0.1	21.4 ± 1.3	35.0 ± 2.5	15.9 ± 1.4
3k	5.2 ± 0.2	11.0 ± 3.4	4.5 ± 0.4	23.9 ± 0.3	39.1 ± 3.3	5.8 ± 0.4
3o	6.1 ± 0.5	5.3 ± 0.3	6.6 ± 0.3	17.5 ± 1.5	37.1 ± 2.1	5.6 ± 0.5
3p	3.7 ± 0.2	4.5 ± 0.2	3.2 ± 0.2	5.6 ± 1.4	30.2 ± 1.7	3.4 ± 0.3
3q	7.0 ± 0.6	11.9 ± 3.2	12.2 ± 4.1	25.2 ± 3.5	37.3 ± 10.7	12.4 ± 2.6
3r	3.1 ± 0.2	3.5 ± 0.4	3.6 ± 0.6	4.6 ± 0.9	38.6 ± 2.4	5.4 ± 0.3
Indirubin-3′-oxime	21.2 ± 1.3	19.2 ± 0.6	36.7 ± 2.0	25.5 ± 3.2	29.5 ± 3.7	37.5 ± 3.8
Roscovitine	8.9 ± 0.1	24.6 ± 1.9^b	7.6 ± 2.2	19.6 ± 2.2^c	17.9 ± 0.8	11.6 ± 1.5

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In summary, this study developed tandem Pd-catalyzed Heck and alkoxycarbonylation reactions for the production of new anticancer agents based on (E)-oxindolylidene acetates. This stereoselective reaction proceeds through the key steps of syn-carbopalladation and alkoxycarbonylation in the presence of CO and alcohols, resulting in only the (E)-configuration of oxindolylidene acetates. We also established the optimal conditions and scope of the reactions. The resulting (E)-oxindolylidene acetates exhibit potent anticancer activity against a variety of human cancer cells.

Experimental section

General procedure for synthesis of N-(2-iodophenyl)-N-(4-nitrobenzyl) propiolamide (1a)

N-(2-Iodophenyl)propiolamide was synthesized with slight modifications according to the reported method.¹⁶ To a solution of N-(2-iodophenyl)propiolamide (400 mg, 1.48 mmol) in DMF (20 mL) was added NaHCO₃ (248 mg, 2.95 mmol) portionwise. The mixture was stirred at 0 °C for 30 min and 4-nitrobenzyl chloride (329 mg, 1.92 mmol) was added dropwise. The reaction mixture was heated to reflux for 6 h until complete by TLC. The reaction was quenched by addition of water and extracted with ethyl acetate. The combined organic layers were washed with brine solution, dried over MgSO₄ and concentrated in vacuo. The residue purified by flash column chromatography furnished the desired N-(2-iodophenyl)-N-(4-nitrobenzyl)propiolamide 1a (463 mg, 77%) as a yellow solid (two rotamers at a ratio of 7 : 1). Mp = 145–147 °C. IR (KBr) ν_max: 3210, 2106, 1646, 1520, 1345, 1310 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) major/minor δ: 8.13/8.16 (d, J = 8.4 Hz, 2H), 7.93/7.89 (dd, J = 7.9, 1.2 Hz, 1H), 7.40/7.42 (d, J = 8.4 Hz, 2H), 7.25/7.21 (dt, J = 7.8, 1.2 Hz, 1H), 7.08/7.01 (dt, J = 7.8, 1.2 Hz, 1H), 6.81/6.71 (dd, J = 7.8, 1.2 Hz, 1H), 5.56/5.58 (d, J = 15.0, 1H), 4.24/4.70 (d, J = 15.0 Hz, 1H), 2.78/3.35 (s, 1H). ¹³C NMR (150 MHz, CDCl₃) major/minor δ: 153.3/152.6, 147.6/147.8, 143.0/142.7, 142.5/141.0, 140.3/140.3, 130.9/129.8, 130.7/129.6, 130.3/130.2, 129.2/129.3, 123.8/123.9, 100.0/98.1, 80.1/80.7, 75.6/75.8, 50.8/54.4. HRMS calcd for C₁₆H₁₂IN₂O₃ (M+1)⁺ 406.9893, found 406.9894.

General procedure for synthesis of (E)-methyl 2-(1-(4-nitrobenzyl)-2-oxoindolin-3-ylidene)acetate (3a)

N-(2-Iodophenyl)-N-(4-nitrobenzyl)propiolamide 1a (200 mg, 0.49 mmol) in CH₃OH (10 mL) was added Pd(OAc)₂ (11 mg, 0.05 mmol), PPh₃ (26 mg, 0.10 mmol) and potassium fluoride (85 mg, 1.47 mmol) in a 25 mL round flask. The flask was evacuated under vacuum and back-filled with carbon monoxide from a balloon. The cycle was repeated three times and the vessel was left open to a dynamic atmosphere of CO. The mixture was then heated to 60 °C under vigorous stirring until complete by TLC. Then the mixture was filtered and concentrated in vacuo. The residue was dissolved in EtOAc and then washed with water. The water phase was extracted with EtOAc (10 mL) twice. The organic layers were combined, dried over MgSO₄ and concentrated. The crude mixture was purified by flash column chromatography to afford the title compound 3a (118 mg, 71%) as a yellowish solid. Mp = 172–174 °C. IR (KBr) ν_max: 3415, 1700, 1602, 1515, 1468, 1342, 1214 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.58 (d, J = 7.8 Hz, 1H), 8.17 (d, J = 8.4 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H), 7.26 (t, J = 7.2 Hz, 1H), 7.07 (t, J = 7.8 Hz, 1H), 6.98 (s, 1H), 6.59 (d, J = 8.4 Hz, 1H), 5.02 (s, 2H), 3.88 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 165.9, 147.6, 144.4, 142.8, 137.4, 132.6, 129.2, 128.0, 124.2, 123.4, 122.9, 120.0, 108.7, 52.3, 43.3. HRMS calcd for C₁₈H₁₄N₂O₅ (M)⁺ 338.0882, found 338.0892.

(E)-Methyl 2-(1-(4-methoxybenzyl)-2-oxoindolin-3-ylidene)acetate (3b). Yield: 67%. Orange solid. Mp = 94–96 °C. IR (KBr) ν_max: 2949, 2921, 1711, 1602, 1511, 1464, 1337, 1199 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.53 (d, J = 8.0 Hz, 1H), 7.26–7.21 (m, 3H), 7.00 (dt, J = 8.0, 1.0 Hz, 1H), 6.95 (s, 1H), 6.83–6.80 (m, 2H), 6.69 (d, J = 8.0, 1H), 4.85 (s, 2H), 3.86 (s, 3H), 3.75 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.6, 166.1, 159.1, 145.2, 138.0, 132.4, 128.8, 128.6, 127.4, 122.8, 122.1, 119.9, 114.2, 109.1, 55.2, 52.1, 43.3. HRMS calcd for C₁₉H₁₇NO₄ (M)⁺ 323.1151, found 323.1154.

(E)-Methyl 2-(1-(4-fluorobenzyl)-2-oxoindolin-3-ylidene)acetate (3c). Yield: 60%. Yellow solid. Mp = 113–115 °C. IR (KBr) ν_max: 3411, 1704, 1606, 1504, 1464, 1344, 1214 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.54 (d, J = 7.8 Hz, 1H), 7.26–7.23 (m, 3H), 7.01 (t, J = 7.8 Hz, 1H), 6.98–6.94 (m, 3H), 6.65 (d, J = 7.8 Hz, 1H), 4.86 (s, 2H), 3.85 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.5, 165.9, 162.2 (d, ¹J_C–F = 245.0 Hz), 144.8, 137.7, 132.4, 131.1 (d, ⁴J_C–F = 2.9 Hz), 128.9 (d, ³J_C–F = 8.1 Hz), 128.8, 122.9, 122.2, 120.0, 115.7 (d, ²J_C–F = 21.3 Hz), 108.9, 52.1, 43.1. HRMS calcd for C₁₈H₁₄FNO₃ (M)⁺ 311.0946, found 311.0952.

(E)-Methyl 2-(1-(4-chlorobenzyl)-2-oxoindolin-3-ylidene)acetate (3d). Yield: 68%. Yellow solid. Mp = 135–137 °C. IR (KBr) ν_max: 3415, 2957, 1700, 1606, 1464, 1344, 1217 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.56 (d, J = 7.8 Hz, 1H), 7.28–7.23 (m, 3H), 7.21 (d, J = 8.4 Hz, 2H), 7.03 (dt, J = 7.8, 1.2 Hz, 1H), 6.96 (s, 1H), 6.64 (d, J = 7.8 Hz, 1H), 4.88 (s, 2H), 3.87 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.6, 166.0, 144.8, 137.8, 133.9, 133.7, 132.5, 129.0, 129.0, 128.6, 123.1, 122.4, 119.9, 108.9, 52.2, 43.2. HRMS calcd for C₁₈H₁₄ClNO₃ (M)⁺ 327.0658, found 327.0660.

(E)-Methyl 2-(1-(4-bromobenzyl)-2-oxoindolin-3-ylidene)acetate (3e). Yield: 64%. Brown solid. Mp = 133–135 °C. IR (KBr) ν_max: 2924, 2844, 1708, 1646, 1606, 1464, 1352, 1203 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.57 (d, J = 6.0 Hz, 1H), 7.60 (d, J = 6.5 Hz, 2H), 7.38 (d, J = 6.5 Hz, 2H), 7.26 (dt, J = 7.0, 1.0 Hz, 1H), 7.05 (dt, J = 6.5, 1.0 Hz, 1H), 6.97 (s, 1H), 6.58 (d, J = 6.5 Hz, 1H), 4.97 (s, 2H), 3.87 (s, 3H). ¹³C NMR (CDCl₃) δ: 167.7, 165.9, 144.4, 140.8, 137.4, 132.7, 132.5, 129.1, 127.8, 123.4, 122.8, 120.0, 118.4, 111.8, 108.7, 52.3, 43.5. HRMS calcd for C₁₈H₁₄BrNO₃ (M)⁺ 371.0135, found 371.0146.

(E)-Methyl 4-((3-(2-methoxy-2-oxoethylidene)-2-oxoindolin-1-yl)methyl) benzoate (3f). Yield: 74%. Yellow solid. Mp = 127–129 °C. IR (KBr) ν_max: 2861, 2224, 1712, 1607, 1469, 1367, 1340, 1214 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.56 (d, J = 6.5 Hz, 1H), 7.96 (d, J = 6.5 Hz, 1H), 7.33 (d, J = 6.5 Hz, 2H), 7.24 (m, 1H), 7.03 (dt, J = 6.0, 0.5 Hz, 1H), 6.97 (s, 1H), 6.61 (d, J = 6.0 Hz, 1H), 4.97 (s, 2H), 3.87 (s, 6H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.7, 166.6, 160.0, 144.7, 140.5, 137.7, 132.5, 130.2, 129.7, 128.9, 127.1, 123.1, 122.5, 119.9, 114.0, 109.0, 52.2, 43.6. HRMS calcd for C₂₀H₁₇NO₅ (M)⁺ 351.1093, found 351.1100.

(E)-Methyl 2-(2-oxo-1-(4-(trifluoromethyl)benzyl)indolin-3-ylidene)acetate (3g). Yield: 70%. Orange solid. Mp = 134–136 °C. IR (KBr) ν_max: 3415, 2917, 1715, 1606, 1352, 1326, 1203, 1119 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.57 (d, J = 6.5 Hz, 1H), 7.56 (d, J = 6.5 Hz, 2H), 7.38 (d, J = 7.0 Hz, 2H), 7.26 (dt, J = 6.5, 1.0 Hz, 1H), 7.04 (dt, J = 6.5, 1.0 Hz, 1H), 6.97 (s, 1H), 6.62 (d, J = 6.5 Hz, 1H), 4.97 (s, 2H), 3.87 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.7, 165.8, 144.6, 139.5, 137.6, 132.5, 130.1 (q, ²J_C–F = 26.9 Hz), 129.0, 127.5, 125.8 (q, ³J_C–F = 2.9 Hz), 123.9 (q, ¹J_C–F = 225.6 Hz), 123.2, 122.6, 119.9, 108.9, 52.2, 43.4. HRMS calcd for C₁₉H₁₄F₃NO₃ (M)⁺ 361.0939, found 361.0932.

(E)-Methyl 2-(1-(4-cyanobenzyl)-2-oxoindolin-3-ylidene)acetate (3h). Yield: 66%. Orange solid. Mp = 192–194 °C. IR (KBr) ν_max: 3400, 2950, 2223, 1697, 1602, 1468, 1344, 1217 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.57 (d, J = 6.0 Hz, 1H), 7.60 (d, J = 6.5 Hz, 2H), 7.38 (d, J = 6.5 Hz, 2H), 7.26 (dt, J = 7.0, 1.0 Hz, 1H), 7.05 (dt, J = 6.5, 1.0 Hz, 1H), 6.97 (s, 1H), 6.58 (d, J = 6.5 Hz, 1H), 4.97 (s, 2H), 3.87 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.7, 165.9, 144.4, 140.8, 137.4, 132.7, 132.5, 129.1, 127.8, 123.4, 122.8, 120.0, 118.4, 111.8, 108.7, 52.3, 43.5. HRMS calcd for C₁₉H₁₄N₂O₃ (M)⁺ 318.1024, found 318.1014.

(E)-Methyl 2-(1-(3-cyanobenzyl)-2-oxoindolin-3-ylidene)acetate (3i). Yield: 51%. Yellow solid. Mp = 95–97 °C. IR (KBr) ν_max: 2861, 2224, 1712, 1607, 1469, 1367, 1340, 1214 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.42 (d, J = 8.4 Hz, 2H), 7.25 (dt, J = 7.8, 1.2 Hz, 1H), 7.24 (s, 1H), 7.15 (d, J = 9.0 Hz, 2H), 7.03 (dt, J = 7.8, 1.2 Hz, 1H), 6.96 (s, 1H), 6.63 (d, J = 7.8 Hz, 1H), 4.86 (s, 2H), 3.87 m (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.6, 166.0, 144.8, 137.7, 134.4, 132.5, 132.0, 128.9, 123.1, 122.4, 121.7, 120.0, 109.0, 52.2, 43.3. HRMS calcd for C₁₉H₁₄N₂O₃ (M)⁺ 318.1018, found 318.1011.

(E)-Methyl 2-(1-(3-chlorobenzyl)-2-oxoindolin-3-ylidene)acetate (3j). Yield: 58%. Yellow solid. Mp = 84–86 °C. IR (KBr) ν_max: 2943, 1711, 1602, 1468, 1337, 1214 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.56 (d, J = 6.5 Hz, 1H), 7.27–7.24 (m, 3H), 7.15 (t, J = 3.5 Hz, 1H), 7.03 (dt, J = 6.5, 0.5 Hz, 1H), 6.96 (s, 1H), 6.64 (d, J = 6.5 Hz, 1H), 4.87 (s, 2H), 3.86 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.5, 165.9, 144.7, 137.6, 137.4, 134.7, 132.5, 130.1, 128.9, 128.0, 127.2, 125.3, 123.0, 122.4, 119.8, 108.9, 52.2, 43.2. HRMS calcd for C₁₈H₁₄ClNO₃ (M)⁺ 327.0675, found 327.0669.

(E)-Methyl 2-(1-(naphthalen-2-ylmethyl)-2-oxoindolin-3-ylidene)acetate (3k). Yield: 59%. Orange solid. IR (KBr) ν_max: 2943, 1711, 1602, 1468, 1337, 1214 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.55 (d, J = 6.5 Hz, 1H), 7.79–7.75 (m, 3H), 7.71 (s, 1H), 7.47–7.42 (m, 3H), 7.38 (dd, J = 6.5, 1.5 Hz), 7.20 (dt, J = 6.5, 1.0 Hz, 1H), 7.02–6.99 (m, 2H), 670 (d, J = 6.5 Hz, 1H), 5.08 (s, 2H), 3.88 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.3, 166.1, 145.1, 138.0, 133.3, 132.8, 132.8, 132.5, 128.8, 128.8, 127.7, 127.7, 126.4, 126.1, 126.0, 125.1, 122.9, 122.3, 119.9, 113.9, 109.3, 52.2, 44.1. HRMS calcd for C₂₂H₁₇NO₃ (M)⁺ 343.1208, found 343.1214.

(E)-Methyl 2-(1-(2-chlorobenzyl)-2-oxoindolin-3-ylidene)acetate (3l). Yield: 57%. Yellow solid. Mp = 106–109 °C. IR (KBr) ν_max: 2371, 1715, 1599, 1472, 1348, 1196 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.57 (d, J = 7.0 Hz, 1H), 7.38 (dd, J = 8.1, 1.0 Hz, 1H), 7.25 (dt, J = 8.0, 1.0 Hz, 1H), 7.20 (dt, J = 7.5, 1.0 Hz, 1H), 7.14 (dt, J = 8.0, 1.5 Hz, 1H), 7.08–7.03 (m, 2H), 6.98 (s, 1H), 6.63 (d, J = 7.5 Hz, 1H), 5.04 (s, 2H), 3.87 (3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.8, 166.0, 144.8, 137.8, 132.8, 132.6, 132.6, 129.7, 128.9, 128.8, 127.8, 127.2, 123.1, 122.4, 119.9, 109.1, 52.2, 41.3. HRMS calcd for C₁₈H₁₄NO₃Cl (M)⁺ 327.0664, found 327.0663.

(E)-Methyl 2-(1-benzyl-2-oxoindolin-3-ylidene)acetate (3m). Yield: 64%. Yellow solid. Mp = 118–120 °C. IR (KBr) ν_max: 2917, 1711, 1602, 1468, 1344, 1195 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.54 (dt, J = 7.5, 0.5 Hz, 1H), 7.32–7.22 (m, 6H), 7.01 (dt, J = 8.0, 1.0 Hz, 1H), 6.96 (s, 1H), 6.67 (d, J = 8.0 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.6, 166.1, 145.1, 137.9, 135.4, 132.4, 128.8, 128.8, 127.7, 127.2, 122.9, 122.2, 119.9, 109.2, 52.2, 43.9. HRMS calcd for C₁₈H₁₅NO₃ (M)⁺ 293.1048, found 293.1050.

(E)-Methyl 2-(1-((3-methylisoxazol-5-yl)methyl)-2-oxoindolin-3-ylidene)acetate (3n). Yield: 55%. Yellow solid. Mp = 131–134 °C. IR (KBr) ν_max: 2957, 1720, 1613, 1470, 1356, 1208 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.33 (t, J = 7.8 Hz, 1H), 7.07 (t, J = 7.8 Hz, 1H), 6.92 (s, 1H), 6.85 (d, J = 7.8 Hz, 1H), 6.00 (s, 1H), 4.96 (s, 2H), 3.86 (s, 3H), 2.22 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.2, 166.0, 165.8, 160.1, 144.1, 137.3, 132.7, 129.0, 123.4, 122.6, 119.8, 108.7, 103.6, 52.2, 35.6, 11.3. HRMS calcd for C₁₆H₁₄N₂O₄ (M)⁺ 298.0959, found 298.0956.

(E)-Methyl 2-(1-(2,6-dichlorobenzyl)-2-oxoindolin-3-ylidene)acetate (3o). Yield: 59%. Orange solid. Mp = 143–145 °C. IR (KBr) ν_max: 3077, 2943, 1711, 1602, 1472, 1435, 1348, 1199 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.52 (d, J = 6.5 Hz, 1H), 7.30 (d, J = 7.0 Hz, 2H), 7.27 (d, J = 7.0 Hz, 1H), 7.19–7.13 (m, 3H), 6.97 (dt, J = 6.0, 1.0 Hz, 1H), 6.91 (s, 1H), 6.61 (d, J = 6.5 Hz, 1H), 5.19 (s, 2H), 3.84 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.2, 166.0, 144.7, 137.6, 136.2, 132.4, 130.0, 129.8, 128.9, 128.7, 122.6, 122.1, 120.0, 109.1, 52.1, 40.1. HRMS calcd for C₁₈H₁₃C_l2NO₃ (M)⁺ 361.0254, found 361.0263.

(E)-Methyl 2-(2-oxo-1-(3,4,5-trimethoxybenzyl)indolin-3-ylidene)acetate (3p). Yield: 68%. Yellow solid. Mp = 145–148 °C. IR (KBr) ν_max: 2943, 2839, 1700, 1595, 1469, 1355, 1204 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.27 (t, J = 7.8 Hz, 1H), 7.03 (t, J = 7.8 Hz, 2H), 6.60 (s, 1H), 6.71 (d, J = 7.8 Hz, 1H), 6.49 (s, 2H), 4.84 (s, 2H), 3.87 (s, 3H), 3.78 (s, 6H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 166.0, 153.5, 145.2, 137.9, 137.5, 132.5, 131.1, 128.8, 123.0, 122.3, 119.9, 109.2, 104.3, 60.8, 56.2, 52.2, 44.2. HRMS calcd for C₂₁H₂₁NO₆ (M)⁺ 383.1369, found 383.1375.

(E)-Methyl 2-(1-(4-chlorobenzyl)-5-methyl-2-oxoindolin-3-ylidene)acetate (3q). Yield: 67%. Yellow solid. Mp = 109–111 °C. IR (KBr) ν_max: 2917, 2845, 1712, 1487, 1352, 1205 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.342 (s, 1H), 7.25 (d, J = 8.4 Hz, 2H), 7.20 (d, J = 8.4 Hz, 2H), 7.05 (d, J = 7.8 Hz, 1H), 6.93 (s, 1H), 6.51 (d, J = 7.8 Hz, 1H), 4.85 (s, 2H), 3.87 (s, 3H), 2.30 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.6, 166.1, 142.6, 138.1, 134.1, 133.6, 132.9, 132.6, 129.5, 129.0, 128.6, 122.0, 119.9, 108.7, 52.2, 43.2, 21.1. HRMS calcd for C₁₉H₁₆ClNO₃ (M)⁺ 341.0798, found 341.0808.

(E)-Methyl 2-(1-(4-chlorobenzyl)-5-methoxy-2-oxoindolin-3-ylidene)acetate (3r). Yield: 64%. Yellow solid. Mp = 169–171 °C. IR (KBr) ν_max: 2987, 2947, 1700, 1642, 1591, 1486, 1337, 1239, 1199 cm⁻¹. ¹H NMR (500 MHz, CDCl₃) δ: 8.27 (d, J = 2.5 Hz, 1H), 7.25 (d, J = 8.5 Hz, 2H), 7.19 (d, J = 8.5 Hz, 2H), 6.95 (s, 1H), 6.80 (dd, J = 8.5, 3.0 Hz, 1H), 6.51 (d, J = 8.5 Hz, 1H), 4.84 (s, 2H), 3.86 (s, 3H), 3.78 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 167.5, 165.9, 155.9, 138.6, 138.3, 134.0, 134.0, 129.0, 128.6, 122.5, 120.6, 118.4, 114.7, 109.4, 55.8, 52.2, 43.3. HRMS calcd for C₁₉H₁₆ClNO₄ (M)⁺ 357.0774, found 357.0771.

(E)-Methyl 2-(1-((6-bromobenzo[d][1,3]dioxol-5-yl)methyl)-2-oxoindolin-3- ylidene)acetate (3s). Yield: 54%. Orange solid. Mp = 203–205 °C. IR (KBr) ν_max: 3427, 2824, 1701, 1603, 1473, 1353, 1201 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.56 (dd, J = 7.8, 0.6 Hz, 1H), 7.27 (dt, J = 7.8, 0.6 Hz, 1H), 7.05 (dt, J = 7.8, 0.6 Hz, 1H), 7.01 (s, 1H), 6.97 (s, 1H), 6.66 (d, J = 7.8 Hz, 1H), 6.55 (s, 1H), 5.90 (s, 2H), 4.93 (s, 2H), 3.88 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.8, 166.0, 148.0, 144.7, 137.8, 132.7, 128.9, 127.3, 123.2, 122.5, 119.9, 113.1, 112.8, 109.3, 107.8, 101.9, 52.2, 43.7. EIMS: 415.26 (M)⁺.

(E)-Methyl 2-(1-methyl-2-oxoindolin-3-ylidene)acetate (3t). Yield: 61%. Yellow solid. Mp = 129–131 °C. IR (KBr) ν_max: 2947, 1711, 1602, 1464, 1435, 1344, 1206 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.58 (d, J = 1.8 Hz, 1H), 7.34 (dt, J = 7.8, 0.6 Hz, 1H), 7.04 (t, J = 1.2 Hz, 1H), 7.02 (d, J = 0.6 Hz, 1H), 6.82 (dd, J = 7.8, 1.2 Hz, 1H), 3.84 (s, 3H), 3.20 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.4, 166.1, 146.0, 138.1, 132.5, 128.7, 122.8, 121.8, 119.7, 108.1, 52.1, 26.2. HRMS calcd for C₁₂H₁₁NO₃ (M)⁺ 217.0722, found 217.0730.

(E)-Methyl 2-(2-oxoindolin-3-ylidene)acetate (3u). Yield: 51%. Yellow solid. Mp = 171–173 °C. IR (KBr) ν_max: 3190, 2917, 1719, 1610, 1464, 1344, 1210 cm⁻¹.¹H NMR (500 MHz, CDCl₃) δ: 8.51 (d, J = 7.5 Hz, 2H), 7.29 (dt, J = 8.1, 1.0 Hz, 1H), 7.02 (dt, J = 8.1, 1.0 Hz, 1H), 6.85 (s, 1H), 6.84 (d, J = 9.0 Hz, 1H), 3.86 (s, 3H). ¹³C NMR (125 MHz, CDCl₃) δ: 169.1, 166.0, 143.4, 138.4, 132.6, 129.0, 122.9, 122.0, 120.3, 110.1, 52.2. HRMS calcd for C₁₁H₉NO₃ (M)⁺ 203.0601, found 203.0592.

(E)-Methyl 2-(1-(4-nitrobenzyl)-2-oxo-5-(trifluoromethyl)indolin-3-ylidene)acetate (3v). Yield: 45%. Orange solid. Mp = 178–180 °C. IR (KBr) ν_max: 3486, 1720, 1618, 1526, 1383, 1210, 1108 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.94 (s, 1H), 8.18 (dd, J = 9.0, 1.8 Hz, 2H), 7.55 (d, J = 7.8 Hz, 1H), 7.43 (d, J = 9.0 Hz, 2H), 7.07 (s, 1H), 6.70 (d, J = 8.4 Hz, 1H), 5.06 (s, 2H), 3.91 (s, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.5, 165.5, 147.8, 146.7, 142.1, 136.1, 129.7 (q, ³J_C–F = 3.5 Hz), 128.0, 126.4 (q, ³J_C–F = 3.9 Hz), 125.9 (q, ²J_C–F = 32.9 Hz), 125.0, 124.3, 123.9 (q, ¹J_C–F = 270.2 Hz), 120.2, 108.6, 52.6, 43.4. HRMS calcd for C₁₉H₁₃F₃N₂O₅ (M)⁺ 406.0777, found 406.0773.

(E)-Ethyl 2-(1-(4-nitrobenzyl)-2-oxoindolin-3-ylidene)acetate (4a). Yield: 62%. Orange solid. Mp = 149–152 °C. IR (KBr) ν_max: 3440, 2924, 2854, 1706, 1608, 1467, 1342, 1202 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.58 (d, J = 7.8 Hz, 1H), 8.16 (d, J = 8.4 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H), 7.26 (dt, J = 7.8, 1.2 Hz, 1H), 7.05 (dt, J = 7.8, 1.2 Hz, 1H), 6.97 (s, 1H), 6.59 (d, J = 7.8 Hz, 1H), 5.01 (s, 2H), 4.33 (q, J = 7.2 Hz, 2H), 1.36 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 165.4, 147.6, 144.3, 142.8, 137.1, 132.4, 129.1, 127.9, 124.1, 123.4, 123.6, 120.0, 108.6, 61.3, 43.2, 14.2. HRMS calcd for C₁₉H₁₆N₂O₅ (M)⁺ 352.1060, found 352.1059.

(E)-Ethyl 2-(1-(4-chlorobenzyl)-2-oxoindolin-3-ylidene)acetate (4b). Yield: 59%. Yellow solid. Mp = 75–77 °C. IR (KBr) ν_max: 2923, 1709, 1604, 1346, 1199 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.27 (d, J = 7.8 Hz, 2H), 7.27–7.23 (m, 1H), 7.21 (d, J = 7.8 Hz, 2H), 7.02 (t, J = 7.8 Hz, 1H), 6.95 (s, 1H), 6.63 (d, J = 7.8 Hz, 1H), 4.88 (s, 2H), 4.32 (q, J = 7.2 Hz, 2H), 1.36 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 165.6, 144.7, 137.4, 134.0, 133.6, 132.4, 129.0, 128.9, 128.6, 123.0, 120.0, 108.9, 61.3, 43.2, 14.2. HRMS calcd for C₁₉H₁₆ClNO₃ (M)⁺ 341.0803, found 341.0811.

(E)-Ethyl 2-(1-(4-bromobenzyl)-2-oxoindolin-3-ylidene)acetate (4c). Yield: 57%. Brown solid. Mp = 107–110 °C. IR (KBr) ν_max: 2988, 1712, 1605, 1359, 1203 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.41 (d, J = 8.4 Hz, 2H), 7.25 (t, J = 7.8 Hz, 1H), 7.14 (d, J = 7.8 Hz, 1H), 7.03 (t, J = 7.8 Hz, 1H), 6.95 (s, H), 6.62 (d, J = 7.8 Hz, 1H), 4.86 (s, 2H), 4.32 (q, J = 7.2 Hz, 2H), 1.36 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 165.6, 144.7, 137.4, 134.5, 132.4, 132.0, 128.9, 128.9, 123.1, 121.7, 120.0, 108.9, 61.3, 43.3, 14.2. HRMS calcd for C₁₉H₁₆BrNO₃ (M)⁺ 385.0314, found 385.0319.

(E)-Ethyl 2-(2-oxo-1-(3,4,5-trimethoxybenzyl)indolin-3-ylidene)acetate (4d). Yield: 64%. Yellow solid. Mp = 168–173 °C. IR (KBr) ν_max: 2996, 1700, 1593, 1356, 1195 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (d, J = 7.8 Hz, 1H), 7.27 (t, J = 7.8 Hz, 1H), 7.03 (t, J = 7.8 Hz, 1H), 6.96 (s, 1H), 6.72 (d, J = 7.8 Hz, 1H), 6.47 (s, 2H), 4.84 (s, 2H), 4.32 (q, J = 7.2 Hz, 2H), 3.79 (s, 3H), 1.36 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.7, 165.6, 153.5, 145.1, 137.6, 137.5, 132.4, 131.2, 128.8, 123.0, 122.9, 120.0, 109.2, 104.3, 61.3, 60.8, 56.2, 44.2, 14.2. HRMS calcd for C₂₂H₂₃NO₆ (M)⁺ 397.1526, found 397.1533.

(E)-Ethyl 2-(5-chloro-1-(4-chlorobenzyl)-2-oxoindolin-3-ylidene)acetate (4e). Yield: 55%. Yellow solid. Mp = 136–139 °C. IR (KBr) ν_max: 2990, 1717, 1606, 1348, 1212 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.59 (d, J = 1.8 Hz, 1H), 7.26 (d, J = 8.4 Hz, 2H), 7.22 (dd, J = 8.4, 1.8 Hz, 1H), 7.17 (d, J = 8.4 Hz, 1H), 6.99 (s, 1H), 6.55 (d, J = 8.4 Hz, 1H), 4.87 (s, 2H), 4.33 (q, J = 7.2 Hz, 2H), 1.37 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.2, 165.2, 143.1, 136.6, 133.8, 133.5, 132.0, 129.1, 129.0, 128.6, 124.5, 121.2, 109.8, 61.5, 43.3, 14.2. HRMS calcd for C₁₉H₁₅Cl₂NO₃ (M)⁺ 376.0507, found 376.0480.

(E)-Ethyl 2-(1-(4-chlorobenzyl)-5-methoxy-2-oxoindolin-3-ylidene)acetate (4f). Yield: 61%. Yellow solid. Mp = 144–149 °C. IR (KBr) ν_max: 2982, 1704, 1652, 1488, 1196 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.26 (d, J = 2.4 Hz, 1H), 7.25 (d, J = 8.4 Hz, 2H), 7.19 (d, J = 8.4 Hz, 2H), 6.95 (s, 1H), 6.79 (dd, J = 8.4, 2.4 Hz, 1H), 6.51 (d, J = 8.4 Hz, 1H), 4.85 (s, 2H), 4.32 (q, J = 7.2 Hz, 2H), 3.78 (s, 3H), 1.35 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.6, 165.5, 155.9, 138.5, 138.0, 134.0, 133.6, 129.0, 128.6, 123.2, 120.7, 118.2, 114.7, 109.4, 61.3, 55.9, 43.3, 14.2. HRMS calcd for C₂₀H₁₈ClNO₄ (M)⁺ 371.0925, found 371.0932.

(E)-Ethyl 2-(1-methyl-2-oxoindolin-3-ylidene)acetate (4g). Yield: 58%. Yellow solid. Mp = 78–81 °C. IR (KBr) ν_max: 2985, 1712, 1608, 1367, 1196 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.53 (d, J = 7.8 Hz, 1H), 7.35 (t, J = 7.8 Hz, 1H), 7.04 (dt, J = 7.8, 0.6 Hz, 1H), 6.89 (s, 1H), 6.77 (d, J = 7.8 Hz, 1H), 4.30 (q, J = 7.2 Hz, 2H), 3.21 (s, 3H), 1.35 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.6, 165.7, 145.9, 137.9, 132.4, 128.7, 122.8, 122.5, 119.8, 108.1, 61.2, 26.2, 14.2. HRMS calcd for C₁₄H₁₁NO₃ (M)⁺ 231.0896, found 231.0896.

(E)-Butyl 2-(1-(3-cyanobenzyl)-2-oxoindolin-3-ylidene)acetate (5a). Yield: 57%. Orange solid. Mp = 134–138 °C. IR (KBr) ν_max: 2957, 1717, 1606, 1468, 1344, 1207 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.58 (d, J = 7.8 Hz, 1H), 7.57–7.55 (m, 1H), 7.53–7.51 (m, 1H), 7.43 (t, J = 7.8 Hz, 1H), 7.27 (t, J = 7.8 Hz, 1H), 7.06 (t, J = 7.8 Hz, 1H), 7.00 (s, 1H), 6.62 (d, J = 7.8 Hz, 1H), 4.94 (s, 2H), 4.27 (t, J = 7.2 Hz, 2H), 1.73–1.69 (m, 2H), 1.45–1.41 (m, 2H), 0.95 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.8, 165.6, 144.3, 137.2, 137.1, 132.4, 131.6, 131.6, 130.7, 129.8, 129.2, 123.5, 123.4, 120.0, 118.4, 113.1, 108.6, 65.2, 43.1, 30.6, 19.1, 13.7. HRMS calcd for C₂₂H₂₀N₂O₃ (M)⁺ 360.1474, found 360.1472.

(E)-Butyl 2-(1-(4-cyanobenzyl)-2-oxoindolin-3-ylidene)acetate (5b). Yield: 53%. Orange solid. Mp = 129–134 °C. IR (KBr) ν_max: 2959, 1703, 1607, 1345, 1199 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.58 (d, J = 7.8 Hz, 1H), 7.59 (d, J = 8.4 Hz, 2H), 7.38 (d, J = 8.4 Hz, 2H), 7.26 (t, J = 7.8 Hz, 1H), 7.06 (t, J = 7.8 Hz, 1H), 6.97 (s, 1H), 6.58 (d, J = 7.8 Hz, 1H), 4.97 (s, 2H), 4.27 (t, J = 6.6 Hz, 2H), 1.73–1.68 (m, 2H), 1.45–1.41 (m, 2H), 0.95 (t, J = 6.6 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 167.8, 165.6, 144.3, 140.9, 137.1, 132.7, 132.4, 129.1, 127.8, 123.4, 123.3, 120.0, 118.4, 111.8, 108.7, 65.2, 43.4, 30.6, 19.1, 13.7. HRMS calcd for C₂₂H₂₀N₂O₃ (M)⁺ 360.1474, found 360.1478.

(E)-Butyl 2-(1-(4-nitrobenzyl)-2-oxoindolin-3-ylidene)acetate (5c). Yield: 55%. Orange solid. Mp = 110–115 °C. IR (KBr) ν_max: 2954, 1709, 1608, 1342, 1204 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.56 (d, J = 8.4 Hz, 1H), 7.37 (dt, J = 7.8, 7.2 Hz, 1H), 7.09 (t, J = 7.8 Hz,1H), 7.00 (d, J = 7.8 Hz, 1H), 6.90 (s, 1H), 4.51 (d, J = 1.8 Hz, 2H), 3.85 (s, 3H), 2.26 (s, J = 1.8 Hz, 1H). ¹³C NMR (150 MHz, CDCl₃) δ: 166.6, 165.9, 144.0, 137.6, 132.5, 128.9, 123.2, 122.4, 120.0, 109.1, 76.5, 72.5, 52.2, 29.3. HRMS calcd for C₂₁H₂₀N₂O₅ (M)⁺ 380.1372, found 380.1347.

(E)-Ethyl 2-(2-oxoindolin-3-ylidene)acetate (4h). Yield: 58%. Yellow solid. Mp = 260–264 °C. IR (KBr) ν_max: 3188, 1718, 1612, 1463, 1323, 1200 cm⁻¹. ¹H NMR (600 MHz, CDCl₃) δ: 8.52 (d, J = 7.2 Hz, 1H), 8.36 (br, 1H), 7.30 (dt, J = 7.8, 1.2 Hz, 1H), 7.03 (dt, J = 7.8, 1.2 Hz, 1H), 6.86 (s, 1H), 6.83 (d, J = 7.8 Hz, 1H), 4.32 (q, J = 7.2 Hz, 2H), 1.35 (t, J = 7.2 Hz, 3H). ¹³C NMR (150 MHz, CDCl₃) δ: 169.1, 165.6, 143.2, 138.0, 132.5, 129.1, 122.9, 122.7, 120.4, 110.1, 61.2, 14.2. EIMS: 217.0 (M)⁺. HRMS calcd for C₁₂H₁₁NO₃ (M)⁺ 217.0739, found 217.0749.

Cancer cell growth inhibition assay

Human cancer cell lines, including human lung adenocarcinoma cell CL 1–5, human epidermoid carcinoma KB, human gastric cancer MKN-45, human breast adenocarcinoma MCF-7, human pancreatic carcinoma MIA Paca-2 and human central nervous system cancer SF-268, were seeded in 96-well plates and incubated for 24 h at 37 °C in a 5% CO₂ incubator. Test compounds were dissolved in dimethylsulfoxide (DMSO) and diluted for cell treatment in culture medium containing DMSO at the final concentration of 0.5%. Cells were treated with test compounds of various concentrations in triplicates per concentration in the culture medium and incubated at 37 °C for 72 h. Actinomycin D of 10 nM and 0.3% DMSO were used as the positive and vehicle controls, respectively. A colorimetric assay using the MTS/PMS system was used to determine the cytotoxic activity of the test compounds. The optical density (OD) values at 490 nm were measured with a 1420-multilabel counter VICTOR from Wallac (Turku, Finland). The IC₅₀, the concentration that inhibited 50% of the cancer cell growth activity, was then determined. All experiments were repeated three times.¹⁷

Acknowledgements

We gratefully acknowledge financial support of the National Science Council (Grant NSC 102-2113-M-077-002-MY2).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Compound characterization and spectral (¹H and ¹³C NMR) data. See DOI: 10.1039/c5ob01863c

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