Intramolecular Hydrogen Abstraction Promoted by Amidyl Radicals. Evidence for Electronic Factors in the Nucleophilic Cyclization of Ambident Amides to Oxocarbenium Ions

Abstract

A tandem 1,5-hydrogen atom transfer/radical oxidation/nucleophilic cyclization mechanism is proposed for the intramolecular hydrogen abstraction reaction promoted for primary carboxamidyl radicals. The electron-withdrawing capacity of the C-5 substituent can switch the reaction to give exclusively bicyclic spirolactams (6-oxa-1-azaspiro[4.5]decan-2-one) when R(1) = H or spirolactones (1,6-dioxaspiro[4.5]decan-2-one) when R(1) = OAc. With a substituent of medium polarity (R(1) = OMe), a mixture of lactones and lactams is formed.