Hexamethylbenzene elimination enables the generation of transient, sterically unhindered multiply bonded boron species

Abstract

We present a method for the generation of boron-containing unsaturated small molecules via hexamethylbenzene elimination. The fragmentation precursors are obtained through bond insertion into phenyl boranorbornadiene (PhB(C6Me6), 1). Compound 1 undergoes 1,1-insertion with 2,6-xylyl isocyanide, affording a boron-doped bicyclo[2.2.2]octa-2,5-diene 2. Heating 2 in toluene results in the formation of a base-stabilized boraketenimine PhB(CNxyl)2 (i.e., borylene diisocyanide) as an intermediate via retro-Diels–Alder reaction. Surprisingly, PhB(CNxyl)2 dimerizes to give a boron-doped 6-membered ring (PhB)2C4(CNxyl)64. The reaction of 1 with trimethylamine N-oxide and phenyl azide yields triphenyl boroxine and a BN4 ring, respectively, implying the involvement of transient oxoborane (PhB[triple bond, length as m-dash]O) and iminoborane intermediates (PhB[triple bond, length as m-dash]NPh), respectively. Furthermore, boranorbornadiene also undergoes 2,3-insertion with mesityl isocyanate (MesNCO), affording a fused 6/5-membered heterocycle 11. This insertion profile is analogous to the insertion of phenyl azide into 1.

Graphical abstract: Hexamethylbenzene elimination enables the generation of transient, sterically unhindered multiply bonded boron species

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Apr 2025
Accepted
16 May 2025
First published
19 May 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2025, Advance Article

Hexamethylbenzene elimination enables the generation of transient, sterically unhindered multiply bonded boron species

C. Zhang, P. Dabringhaus, B. Y. E. Tra, R. J. Gilliard and C. C. Cummins, Chem. Sci., 2025, Advance Article , DOI: 10.1039/D5SC02645H

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