Multicomponent Cascade Reactions Triggered by Cycloaddition of Fischer Alkoxy Alkynyl Carbene Complexes with Strained Bicyclic Olefins

A broad range of substituted 2-cyclopentenone derivatives are prepared by a multicomponent sequential reaction of chromium alkoxy alkynyl carbene complexes with strained bicyclic olefins. An unprecedented behavior of the carbene complexes, which react through the carbene carbon and both acetylenic carbons, in a [2+2+1]/[2+1] cascade sequence, allows the synthesis of multicomponent products, which (a) incorporate two units of the same strained bicyclic olefin, (b) incorporate two different olefins, and/or (c) involve intramolecular [2+1] reactions. Evidence of the formation of 2-cyclopentenone-derived Fischer carbene complexes as reaction intermediates is provided, as they are trapped with different types of olefins or undergo alkyne insertion.