THEORETICAL AND EXPERIMENTAL-STUDY OF THE REGIOSELECTIVITY OF THE REACTION OF DIAZOMETHANE WITH ALLENE

The reaction of diazomethane with allene at room temperature afforded a mixture of 4-methylene-1-pyrazoline (1) and 3-methylene-1-pyrazoline (2) in a 93:7 ratio. This finding revises literature data which descr ibe this reaction as regiospecific with exclusive formation of 1. Good level ab-initio calculations (e.g., HF/6-31G//HF/6-31G*, MP4SDTQ/6-3 1G//HF/6-31G* and MP4SDTQ/6-31G*//MCSCF/3-21G) qualitatively reproduc e the experimental regiochemical ratio.