Reaction of 2, 4- diphenyl-4, 5-dihydro-1, 3-oxazol-5-one with 4-phenyl-N-tosyl-1azabuta-1, 3-diene; CC versus CN double bond addition

Abstract

The reaction of 2, 4-diphenyl-4, 5-dihydro-1, 3-oxazol-5-one 1 with 4-phenyl-N-tosyl-1-azabuta-1, 3-diene 2 has been investigated using different experimental conditions. Whereas at room temperature the kinetically controlled Michael adduct 3 was isolated, at 110 °C products 4, 5, 6 and 7 were obtained. Their formation is explained according to 1,3-dipolar cycloaddition and nucleophilic addition, both related to the dual nature of the azlactone 1. The reactivity of azlactone 1 towards imine 2, which is different from that observed with N-alkyl- and N-aryl-1-azabuta-1,3-dienes, is explained on the basis of the electronic effects exerted by the tosyl substituent.