Stereoselectivity of the Radical Reductive Alkylation of Enamines: Importance of the Allylic 1,3‐Strain Model

Radical addition to enamines using Bu3SnH as reducing agent are reported (Schemes 2 and 4). The diastereoselectivity of these reactions was examined in different systems (Tables 1 and 2). Enamines derived from cyclic ketones such as cyclohexanone were alkylated with high diastereoselectivity with preferential formation of the cis‐disubstituted cycloalkanes. In acyclic systems such as enamines derived from propiophenone and diethyl ketone, moderate to high stereoselectivities were observed in the H‐abstraction step. A model based principally on minimization of allylic 1,3‐strain (A1,3 strain) was deduced from the experimental results and semi‐empirical (AM1) calculations.