Protodestannylation of carbomethoxy-substituted vinylstannanes: Kinetics, stereochemistry, and mechanisms

Article abstract of DOI:10.1021/om00105a036

Five carbomethoxy- and four carboethoxy-substituted vinylstannanes have been prepared. Methyl 2-(trimethylstannyl)acrylate and ethyl 2-(trimethylstannyl)acrylate were prepared by hydrostannation of methyl and ethyl propiolate under polar conditions. The former compound was also prepared by Pd(0) catalyzed hydrostannation of methyl propiolate. The E and Z isomers of methyl and ethyl 3-(trimethylstannyl)acrylate were prepared by free radical hydrostannation of methyl and ethyl propiolate. Methyl and ethyl 2-(trimethylstannyl)fumarate were synthesized by hydrostannation of dimethyl and diethyl acetylenedicarboxylate under polar conditions. Methyl 2-(trimethylstannyl)maleate was prepared by Pd(0)-catalyzed hydrostannation of dimethyl acetylenedicarboxylate. Structures were confirmed by ¹H and ¹³C NMR. The stereochemistry of stannyl cleavage was determined by deuteriodestannylation and ¹H NMR of the products. The methyl 3-(trimethylstannyl)acrylate isomers gave retention of configuration while the methyl 2-(trimethylstannyl)fumarate and -maleate resulted in approximately equal ratios of isomeric deuteriodestannylation products. In this latter case an allenol intermediate is proposed. Second-order rate constants for protodestannylation, in methanol-5% water, were determined at three temperatures for the carbomethoxy compounds. Activation parameters were calculated from the rate data. The carbomethoxy group was found to be deactivating for all compounds except methyl 2-(trimethylstannyl)maleate. In this case, interaction of the syn carbomethoxy groups may serve to provide a more reactive route to the allenol intermediate.