Aryl radical cyclizations onto enamine double bonds

Abstract

Aryl radicals from N-alkyl-N-(2-bromobenzyl)-1-cyclohexenylamine 2 and N-alkyl-N-(2-bromobenzyl)-cyclopentenylamine 11 cyclize readily onto the enamine double bond by 6-endo and 5-exo closure. In the case of 2, 6-endo cyclization is the major pathway; however, the 6-endo to 5-exo ratio is dependent upon the N-alkyl substituent. In both cases, the dominant isomer from 6-endo cyclization is the cis isomer. For 2a in toluene, values of k 6-endo and k 5-exo at 80 o C were 4.6×10 8 s -1 and 1.5×10 8 s -1 , respectively