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Generation of Bis(pentafluorophenyl)boron Enolates from Alkynes and Their Catalyst-Free Alkyne Coupling
Masatoshi Shibuya1, Souta Yuruka2, Yoshihiko Yamamoto2
1Department of Chemical and Biological Sciences, Faculty of Sciences, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo 112-8681, Japan.
Abstract:
Carbon-carbon bond forming reactions are powerful synthetic tools for constructing organic molecular frameworks. In this study, strongly Lewis acidic bis(pentafluorophenyl)boron enolates were generated from alkynes through oxygen transfer from 2,6-dibromopyridine N-oxide using tris(pentafluorophenyl)borane [B(C6F5)3]. Boron enolates were highly reactive owing to the strong Lewis acidity of the boron centers, and thus immediately coupled with alkynes. N-Ethynylphthalimide reacted as an alkyne with 2,6-dibromopyridine N-oxide and B(C6F5)3 to form a semi-stable bis(pentafluorophenyl)boron enolate through the coordination of the carbonyl group to the boron center. This enolate underwent coupling with another alkyne.
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