A Convenient Stereocontrolled Route to Trifluoromethylated Penta-2E,4E-
or 2Z,4E-dienenitriles

Abstract

The phosphoryl-stabilized carbanions 2, generated from the corresponding phosphonates and lithium diisopropylamide in tetrahydrofuran, were used to add regiospecifically to [(trifluoroacyl)cyanomethylenetriphenylphosphorane] (1) forming ylide anions 3. After protonation and elimination of triphenylphosphine oxide from 3, trifluoromethylated cyanoallylphosphonates 4 were obtained in 74-95% yields with high Z-stereoselectivity (4a-c) or E-stereoselectivity (4d-h) depending upon the structure of the phosphoryl-stabilized carbanions 2 used. The E- and Z-isomers of 4 could be separated conveniently by column chromatography. Treatment of Z-4 or E-4 with sodium hydride gave an anion which reacted with aldehydes affording the trifluoromethylated penta-2E,4E- or 2Z,4E-dienenitriles exclusively or predominantly in 52-71% yields. Their structures were determined by X-ray crystallographic analysis.

Key words

trifluoromethylated penta-2E,4E- or 2Z,4E-diene­nitriles - trifluoromethylated - cyanoallylphosphonates - stereocontrol - fluorine-containing compounds - X-ray crystallographic analysis

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11

Crystallographic data for the compounds 9 and 8a have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-186256 (9) and CCDC-186257 (8a). Copies of data can be obtained free of charge on application to CCDC 12 Union Road Cambridge CB2 1EZ UK [fax:[phone] or e-mail: [e-mail]].