Theoretical studies on cycloaddition reactions of 2-azaallene cations with isocyanates

The mechanisms of cycloaddition reactions between 2-aza-allene cations and isocyanates have been explored at the B3LYP/6-31G(.) level. It is found that [2+2] or [2+4] cycloaddition reactions can take place via an intermediate when 2-azaallene cations react with 1 or 2 equiv. of isocyanates. The effects of substituents are also reported in the present paper, and the results obtained indicate that electron-attracting groups on 2-azaallene cations favor the reaction, and electron-donating groups on 2-azaallene cations hinder the reaction. Substituents on isocyanates have the opposite effects. These results have been rationalized with FMO interaction. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).