General and efficient insertions of carbons carrying aryl and heteroaryl groups: Synthesis of alpha-aryl- and alpha-heteroaryl-substituted ketones

Anions formed from the lithiation of a variety of 1-(arylmethyl)- and 1-(heteroarylmethyl)benzotriazoles 1 with n-BuLi underwent addition to aliphatic and aromatic aldehydes and cyclic and acyclic ketones. Subsequent in situ thermal rearrangements of the intermediates in the presence of zinc bromide provided one-carbon chain-extended or ring-expanded alpha-aryl- and alpha-heteroaryl-substituted ketones 2 in moderate to excellent yields in simple one-pot operations with excellent regioselectivity in most cases. Substituent effects on the relative migration rates were investigated in the insertion reactions of 1-(4-methoxybenzyl)benzotriazole (1e) with XC(6)H(4)-COPh. The small and negative Hammett rho(+) value (-0.92) suggested that the rearrangements proceed via early, reagent-like, electron deficient transition states.