Heterogeneous rate constants for indium mediated allylations: cinnamyl chloride in ethanol/water mixtures.

Indium mediated allylation (IMA) offers a powerful tool to synthetic chemists for creating carbon-carbon bonds. However, its rate limiting step, the heterogeneous reaction of allyl halides at solid indium surfaces, is still poorly understood. For example, solvent effects, especially the presence of water, on IMA are dramatic.

Measurement of heterogeneous reaction rates: three strategies for controlling mass transport and their application to indium-mediated allylations.

We describe three new strategies for determining heterogeneous reaction rates using photomicroscopy to measure the rate of retreat of metal surfaces: (i) spheres in a stirred solution, (ii) microscopic powder in an unstirred solution, and (iii) spheres on a rotating shaft. The strategies are applied to indium-mediated allylation (IMA), which is a powerful tool for synthetic chemists because of its stereoselectivity, broad applicability, and high yields. The rate-limiting step of IMA, reaction of allyl halides at indium metal surfaces, is shown to be fast, with a minimum value of the heterogeneous rate constant of 1 × 10(-2) cm/s, an order of magnitude faster than the previously determined minimum value.