3‐Aminoidoles, Imidazolidines, and Oxazolidines from Isocyanides and Carbene Complexes by Metal‐Induced [4+2]‐ and [3+2]‐Cycloadditions

Abstract

the azaalene complexes 1 (M = Cr, Mo, W) are especially useful building blocks in the synthesis of heterocycles. They undergo [3 + 2]-cycloadditions with aldehydes, isocyanates or carbodiimides to give carbene complexes such as 2, from which the carbonylmetal fragment can be oxidatively cleaved such that the corresponding five-membered ring heterocycles are formed. For example, the hydantoin 3 can be obtained in high yields from the isocyanate adduct 2 (X = NR″, Y = O).