FORMATION OF ACYL-SUBSTITUTED NITRILE YLIDES BY RH-2(OAC)(4)-CATALYZED DECOMPOSITION OF ALPHA-DIAZOCARBONYL COMPOUNDS IN NITRILES

The Rha(OAc)(4)-catalyzed reactions of alpha-diazocarbonyl compounds i n nitrile in the presence of dimethyl acetylenedicarboxylate (DMAD) ga ve oxazole and pyrrole derivatives. The formation of the oxazole deriv atives is explained in terms of the 1,5-cyclization of an acyl-substit uted nitrile ylide intermediate, and the formation of the pyrrole deri vatives is explained by the 1,3-dipolar cycloaddition of the same inte rmediate with DMAD. The regiochemistry of the cycloaddition of the acy l-substituted nitrile ylide with methyl propiolate showed that the con tribution of an allenyl-type resonance structure plays an important ro le in the acyl-substituted nitrile ylide reaction.