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DOI: 10.1055/s-2005-921722
Radical α-Trifluoromethylation of Ketones via Lithium Enolates
Y. Itoh, K. Mikami*
Tokyo Institute of technology, Japan
Publication History
Publication Date:
16 December 2005 (online)
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Significance
So far the trifluoromethylation of ketones was known only via preparation of some derivatives, which makes the whole process lengthy. Although, perfluoroalkylation is known to give products in good yields (K. Miura, Y. Takeyama, K. Oshima, K. Utimoto Bull. Chem. Soc. Jap. 1991, 64, 1542-1553). Interestingly, this radical trifluoromethylation reaction was found to be extremely fast and is completed often within seconds at -78 ºC. Prolonged reaction times often decrease the yields of the products probably due to base-induced decomposition. Only cyclic ketones were studied as substrates. The lithium enolate can be generated from a ketone by a direct metalation (‘kinetic’ enolate) or from its trimethylsilyl enol ether by reaction with BuLi (‘thermodynamic’ enolate). Since even 20 mol% of Et3B is sufficient for good yields, a radical chain mechanism involving formation of the CF3 radical and its attack on the enolate is proposed. No reaction was observed in the absence of Et3B.