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Published on: September 8, 2013
Electrophilic Cyanation of Boron Enolates: Efficient Access to Various β-Ketonitrile Derivatives
Kensuke Kiyokawa1, Takaya Nagata2, Satoshi Minakata3
1Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka, 565-0871, Japan. kiyokawa@chem.eng.osaka-u.ac.jp.
Abstract:
The highly efficient electrophilic cyanation of boron enolates using readily available cyanating reagents, N-cyano-N-phenyl-p-toluenesulfonamide (NCTS) and p-toluenesulfonyl cyanide (TsCN), is reported. Various β-ketonitriles were prepared by this new protocol, which has a remarkably broad substrate scope compared to existing methods. The present method also allowed efficient synthesis of β-ketonitriles containing a quaternary α-carbon center. In addition, a preliminary result with the use of a chiral boron enolate for the enantioselective cyanation reaction is described.
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One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Nitrosation of Enols
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Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.

