Reaction of 1‐oxa‐3‐azabutatrienium salts with tertiary carboxamides

α‐Chloro isocyanates 1 react with tertiary carboxamides or acylimines 3 in the presence of Lewis acids (SbCl 5 , FeCl 3 ) to give the amino‐substituted 2‐azaallenium salts 5a – t under mild conditions. With methanol the moderately strong electrophiles 5 afford the acetals 8 and 10 . According to an X ‐ray structural analysis, the C N C unit of 5a is bent by 128°. There exists a linear relationship between the wave number of the antisymmetric stretching vibration of 2‐azaallenium salts and the bond angle. The planes defined by the sp 2 carbons of the moiety of 5a are almost perpendicular (84°) with respect to each other.