Anti-Beckwith stereoselectivity in amidyl radical cyclisations: Bu3SnH-mediated 5-exo-trig acyl mode cyclisation of 2-substituted pent-4-enamide radicals

2-Substituted amidyl radicals derived from 8a–d and 9a–d undergo acyl mode 5-exo-trig cyclisation to give 3,5-trans pyrrolidinones 11a–d and 14a–d as the major products in low diastereoselectivity (de = 9–36%). The steric nature of the nitrogen substituent attached to the amidyl radical does not have a significant effect on selectivity. The stereochemical outcome is opposite to that expected based upon applying the Beckwith rule.