Ligand Effects on the Diastereoselectivities of Samarium Diiodide Promoted Pinacol Coupling

Abstract

The samarium diiodide pinacol coupling of benzaldehyde and cyclohexanecarboxaldehyde in the presence of a variety of polyethylene glycols, including derivatives containing carbohydrates has been studied. Whereas such complexing agents allow for the formation of 1,2‐diols, in the case of benzaldehyde the erythro‐isomer predominates with diastereoselectivities of up to 7:1, while with cyclohexanecarboxaldehyde a stereoselectivity of up to 10:1 was observed but in favor of the threo‐isomer. This divergence in the stereoselectivity of these two aldehydes suggests the presence of two different mechanisms occurring in these pinacol coupling reactions.

Mechanistic Studies of Proton‐Donor Coordination to Samarium Diiodide

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Alcohols, glycols, and glymes are commonly used as additives in numerous reductions and reductive coupling reactions of samarium diiodide (SmI 2 ). All of these additives have been shown to exert an influence on the regiochemical [3,4] and stereochemical [5,6] outcomes of numerous SmI 2 -mediated reactions. All of these additives have been shown to exert an influence on the regiochemical [3,4] and stereochemical [5,6] outcomes of numerous SmI 2 -mediated reactions.

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