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O–H hydrogen bonding promotes H-atom transfer from α C–H bonds for C-alkylation of alcohols

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Science  25 Sep 2015:
Vol. 349, Issue 6255, pp. 1532-1536
DOI: 10.1126/science.aac8555

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A trio helps activate C-H bonds in alcohols

Enzymes can accelerate chemical reactions by activating specific portions of a molecule through well-placed H bonds. Jeffrey et al. showcase the power of H-bonding in a synthetic context. Here, reactivity at the C centers of alcohols is selectively induced by using an H-bonding catalyst to bind the hydroxyl group of the alcohol. The adjacent C-H bonds now become susceptible to a reaction accelerated by another pair of catalysts. In combination, the trio of catalysts promotes C-C bond formation at the alcohol C within an array of competing sites.

Science, this issue p. 1532

Abstract

The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C–H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds.

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