Rearrangements of Oxocyclopropanecarboxylate Esters to Vinyl Ethers. Disparate Behavior of Transition-Metal Catalysts

Article abstract of DOI:10.1021/jo00148a020

Diverse transition-metal compounds catalyze the conversion of 2-alkoxycyclopropanecarboxylate esters to derivative vinyl ethers in high yield under mild conditions.With 2, PtCl2*2PhCN, or 2, structural rearrangement occurs with concurrent epimerization of the reactant cyclopropane compound, and identical isomeric mixtures of vinyl ethers are formed from either of the two stereoisomeric cyclopropane reactants.Rhodium(II) acetate catalyzed reactions occur at higher temperatures than those required with 2, epimerization of the (Z)-cyclopropane isomer, but not the E isomer, is observed, and individual stereoisomeric cyclopropane reactants produce different isomeric mixtures of vinyl ether products.The characteristics of copper bronze and copper(I) chloride catalyzed reactions are generally similar to those of Rh2(OAc)4, except with ethyl 2-methoxy-2-vinylcyclopropanecarboxylate, which undergoes rearrangement to the isomeric ethyl 3-methoxycyclopentenecarboxylates in the presence of these copper catalysts.Participation by the carbethoxy group in rhodium(I)-, platinum (II)-, and ruthenium(II)-catalyzed reactions is indicated in results from comparative reactions with nitrile and sulfone derivatives, and the mechanistic involvement of a six-membered ring metallocycle is suggested.In rhodium(II)- and copper-catalyzed reactions, metallocyclobutane intermediates are proposed to account for their contrasting results.Catalytic rearrangement of (allyloxy)cyclopropanecarboxylate esters affords 3-allyl-4-oxoalkanoate esters in good yield by a synthetic coupling of the oxocyclopropane-vinyl ether and Claisen rearrangement transformations.