Generation and reactions of 2-alkoxydiphenylcarbenes in fluid solution and rigid matrices

Abstract

Irradiation of 2-alkoxydiphenyldiazomethanes 1 in cyclohexane at room temperature produced 3-phenyldihydrobenzofurans 3 presumably as a result of intramolecular C–H insertion of 2-alkoxydiphenylcarbenes 2. Irradiation of compounds 1 in cyclohexane matrix at –196 °C gave intermolecular C–H insertion products 4 at the expense of benzofurans 3. The formation of products 4 is explicable in terms of H-atom tunnelling to the triplet state of carbenes 2, followed by coupling of the resulting radical pairs. Product ratios 3:4 were somewhat sensitive t o the bulk of the alkoxy group at the 2-position. This can be explained in terms of the matrix effect on the relative population of the rotational isomers of the carbene 2.

Irradiation of compounds 1 in methanol at room temperature afforded O–H insertion products 5 almost exclusively, whereas irradiation in methanol matrix at –196 °C gave C–H insertion products 6 along with other products 3 and 5.