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.
Katritzky
Alan R.
AR
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200.
Toader
Dorin
D
Xie
Linghong
L