1,2-asymmetric induction in reactions of nonconjugated acyclic radicals: A new model for highly selective atom-transfer reactions of alkyl-substituted radicals

Article abstract of DOI:10.1021/ja00072a010

The iodine-transfer addition of methyliodomalonodinitrile (1) to several dialkyl-substituted olefins is reported. The iodine-transfer reaction to the acyclic nonconjugated radical intermediates often results in selective product formation due to 1,2-asymmetric induction. The level of diastereoselectivity depends on the size of the alkyl substituent on the radical. Tertiary alkyl groups give high syn selectivity, secondary groups lead to a moderate syn selectivity, and primary groups show completely unselective reactions. To explain the stereochemical outcome, a new steric model of the ^tBu-substituted radical 5e is introduced on the basis of AM1 calculations and EPR data. This transition-state model is unusual in that it postulates attack of the reagent on the radical between the medium and large groups and anti to the small group.