Chemistry

Switching Preferences

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Science  20 Dec 2002:
Vol. 298, Issue 5602, pp. 2287
DOI: 10.1126/science.298.5602.2287c

In designing organic reaction routes, synthetic chemists assess whether the groups on carbons atoms are nucleophilic (preferring to react at positively charged sites) or electrophilic (seeking out negative charge). In the closing of internal rings in molecules, a bond might be formed most conveniently between two carbon atoms that, inconveniently, bear groups with similar nucleophilicity. Mihelcic and Moeller use anodic electrochemisty to turn this liability into an asset by performing an umpolung reaction—a trick, used by some enzymes, that switches the polarity at a particular carbon atom. In their synthesis of the tricyclic alliacol A, the formation of a radical cation during the oxidation of an silylenol ether allowed its normally nucleophilic β-carbon atom to attack an electron-rich furan ring to form a six-membered ring in high yield (88%). The final ring was created via Friedel-Crafts alkylation. Unlike other electrochemical approaches, anodic oxidation could be executed with only a vitreous carbon anode and a 6-volt lantern battery. — PDS

J. Am. Chem. Soc. 10.1021/ja029064v.

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