Tuesday, July 15, 2008

C-C bond forming by Si-C cleavage

J. Org. Chem., 61 (20), 6901 -6905

Carbon-carbon bond formation is often considered the most difficult challenge in synthetic organic chemistry, and new or improved solutions to carbon-carbon bond-forming reactions are continuously being sought. One of the most useful categories of reagents for this purpose is the organometallic carbon nucleophiles, including organolithium, organomagnesium, and organocopper compounds.1 Unfortunately, these reagents do have limitations. Since they are extremely strong bases as well as potent nucleophiles, their use with base sensitive substrates is precluded. Organolithium and -magnesium reagents are incompatible with halo, nitro, and cyano functionalities. Finally, benzylic and allylic organometallics are notoriously difficult to generate and prone to homocoupling.1

An alternative methodology that circumvents these limitations is the generation of stabilized carbanions or carbanoids by cleavage of silicon-carbon bonds using fluoride anion.2 The most commonly used fluoride source for this purpose is tetrabutylammonium fluoride (TBAF). The superiority of tetrabutylammonium triphenyldifluorosilicate (TBAT) to TBAF as a fluoride source for nucleophilic fluorination3 is described.

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