CHEMISTRY: Beyond the Basics

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Science  25 Feb 2005:
Vol. 307, Issue 5713, pp. 1171c
DOI: 10.1126/science.307.5713.1171c

The formation of carbon- carbon bonds via enolate addition to electrophiles is a cornerstone of modern organic synthesis. These types of reactions are generally started by treating a ketone with a base, which deprotonates the carbon atom adjacent to the carbonyl group, leaving a negatively charged O-C-C framework that is the target of the electrophile. However, the product is also a ketone and hence is susceptible to repeated attack by the base, leading to losses in stereoselectivity and undesirable side reactions.

Trost and Xu have found a way around this problem by eliminating the base. They stabilized precursors in the enol form by tethering the electrophile (an allyl group in this case) to the enol oxygen through a carbonate (OCO2) linkage. Activation of the allyl group by an asymmetric palladium catalyst liberates the CO2 spacer and allows the enol and allyl carbons to join without a deprotonation step. This reaction provides access to a broad range of tertiary and quaternary carbon centers in good yield and enantioselectivity, while minimizing side reactions. — JSY

J. Am. Chem. Soc. 10.1021/ja043472c (2005).

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