New alkaloid-like heterocycles via formal aza-[3+2] cycloaddition reaction of cyclic enaminones with cyclopropenones

The formal aza-[3+2] cycloaddition reactions of cyclopropenones and cyclic enaminones, including a chiral one, were employed for the first time in the direct formation of new pyrrolidine and indolizidine derivatives. The regiochemistry of cyclization is dependent of both ring size and steric factors of enaminones.