[3+2] and [4+1] Cycloaddition Reactions of Fischer Alkoxy(alkenyl)carbene Complexes with Electronically Neutral 1,3‐Dienes

Regio- and stereochemically controlled formation of cyclopentenes has been achieved through the reaction of transition-metal–alkoxy(alkenyl)carbene complexes and neutral 1,3-dienes (see scheme; BHT=2,6-di-tert-butyl-4-methylphenol). Reaction conditions dictate whether [3+2] or [4+1] cycloaddition products are obtained; alkenyl-substituted cyclopentanones of high enantiomeric purity are synthesized by using 8-phenylmenthyloxycarbene complexes.