[3+2]-Versus [4+2]-cycloaddition reactions of 3-methylsulfanyl-2-arylazo-3-(pyrrolidin-l-yl)acrylonitriles with N-substituted maleimides involving pyrrolidine-derived azomethine ylides

摘要

3-Methylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles do not enter into [4+2]-cycloaddition reactions with male-imides to form the expected pyrrolo-pyridazines.Instead the formation of novel pyrrolo-pyridazines of type 4 takes place via a for-mal [3+2]-cycloaddition of initially formed pyrrolidine-derived azomethine ylides 7.The mechanism leading to the final product is discussed.