Generation of carbonyl ylide dipoles from the Rh(II) -catalyzed cyclization of alpha-diazo-beta-keto-1,5-diesters

The Rh(II)-catalyzed reaction of ethyl 2-diazo-3-[1-(ethoxycarbonyl)cyclopr opyl]-3-oxopropanecarboxylate with various dipolarophiles afforded dipolar cycloadducts in good yield. The reaction involves the formation of a rhodiu m carbenoid and subsequent transannular cyclization of the electrophilic ca rbon onto the remote ester carbonyl group to generate a five-membered cycli c carbonyl ylide which undergoes a subsequent dipolar cycloaddition reactio n. In the absence of a trapping agent, a head to tail coupling of the 1,3-d ipole intermediate occurs to give a dimer. Heating a benzene solution of th e dimer at 80 degreesC in the presence of various dipolarophiles gave the s ame cycloadducts as was obtained from the Rh(II)-catalyzed reaction.