1,3-dipolar cycloaddition of 1-phenylpropa-1, 2-diene with pyridinium dicyanomethylides : 1-phenylpropa-1, 2-diene as a synthetic equivalent of 1-phenylpropyne

Pyridinium dicyanomethylides (1)underwent 1, 3-dipolar cycloaddition with 1-phenyl-propa-1,2-diene (2) to give a mixture of 3-cyano-2-methyl-1-phenylindolizines (4) and 3cyano-1-methyl-2-phenylindolizines (5), accompanied by dehydrocyanation and 1,3-sigmatropic hydrogen shift.