Cyclization or Hydrogen Migration: Theoretical Study and Experimental Evidence on the Reactivities of Unsaturated Amidyl Radicals

[reaction: see text] Theoretical calculations (B3LYP/6-31G) backed up by deuterated experiments reveal that the N-substituents (R) play a crucial role in determining the reaction pathways of unsaturated amidyl radicals. With the increase of the bulkiness of N-alkyl group, the activation energy for 6-exo cyclization increases steadily, while the activation energy for 1,5-H abstraction remains almost unchanged. Therefore, cyclization occurs exclusively when R is H while 1,5-H migration occurs exclusively when R is t-Bu.