Science of Synthesis

Vaultier, M.; Pucheault, M., Science of Synthesis Knowledge Updates, (2012) 4, 306.

The transition-metal-catalyzed silaborative C—C bond cleavage reactions of methylenecyclopropanes follow various pathways, depending on the catalysts that are used and the structure of the reactant. For example, treatment of 7-methylenebicyclo[4.1.0]heptane with pinacol [dimethyl(phenyl)silyl]boronate in the presence of 1:1.2 mixture of bis(dibenzylideneacetone)palladium(0) and triphenylphosphine in toluene at 50 °C results in cleavage of the proximal C—C bond and regioselective introduction of a silyl and a boryl group to give the corresponding vinylboronate in 64% yield after 24 hours.[‌18‌] This type of reaction can be applied in a desymmetrization of meso-methylenecyclopropanes using a palladium catalyst bearing an optically active monodentate phosphorus ligand. Optimal enantioselectivity in this reaction is achieved using the binaphthylphosphine ‌21‌.[‌18‌] Under these conditions, a variety of meso-methylenecyclopropanes undergo asymmetric silaborative C—C cleavage. Bicyclic methylenecyclopropanes give the corresponding vinylboronates in high yields and high enantioselectivities (‌Table 2‌, entries 1, 2 and 4), whereas a nonfused substrate gives a lower enantiomeric excess (entry 3).

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References