An ab initio study of substituent effects on the electrocyclization of silyloxyazadienes

The electrocyclization of 4-substituted 3-silyloxy-2-azadienes to beta-lactams was studied at the MP2/6-31G* level of theory and the effect of the substituents on the reactivity of the azadiene and on the stereochemistry of the cyclic products was evaluated. It was shown that the electrocyclization is favoured when the substituent in 4-position is in the (Z) configuration and discloses an electron-donor effect. The cyclization reactions generally lead to trans (beta-lactams, but with a basic substituent cis beta-lactams are obtained as well.