Synthesis and application of novel bicyclic guanidines: N-alkylation of 1,5,7-triazabicyclo[4.4.0]dec-5-ene

Abstract

The regioselective ring-opening reaction of optically pure epoxides by 1,5,7-triazabicyclo[4.4.0]dec-5-ene was employed to prepare enantiomerically pure guanidine bases. A further example was prepared by deprotonation of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene followed by trapping with ()-camphor. Four of these bases were evaluated in the asymmetric epoxidation of 3-tert-butoxycarbonylamino-4,4-dimethoxycyclohexa-2,5-dien-1-one (4) and trans-chalcone using t-butyl hydroperoxide. Reasonable yields of the epoxide were obtained from the chalcone reaction but the ee's were low; with the quinone monoacetal 4 ee's in the range 29-35% were obtained.