The transient 8 pi 1,7-dipolar azafulvenium methides 5 and 8 undergo sigmat
ropic [1,8] H shifts and the acyl derivatives 12 electrocyclise to give nov
el pyrrolooxazines 13; the related diazafulvenium methide 15 can be interce
pted in 8 pi + 2 pi cycloadditions with silylated acetylenes.