Substituent effects, reactant preorganization, and ligand exchange control the reactivity in RhI-catalyzed (5+2) cycloadditions between vinylcyclopropanes and alkynes

Abstract

(Chemical Equation Presented) Heteroatom and bulky alkyl substituents dramatically increase the rate of RhI-catalyzed (5+2) cycloadditions of 1. This fact could be attributed to steric effects which ease the reactant preorganization, and to the stabilization of the allyl intermediate by (hyper) conjugation with the substituents. The methoxy- and isopropyl-substituted 1 have an activation energy 5 and 7 kcal mol-1, respectively, lower than the unsubstituted vinylcyclopropane. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.