Journal of Organic Chemistry 2006-10-27

Pathway for the stereocontrolled Z and E production of alpha,alpha-difluorine-substituted phenyl butenoates.

Wadih Ghattas, Corinna R Hess, Gilles Iacazio, Renaud Hardré, Judith P Klinman, Marius Réglier

Index: J. Org. Chem. 71(22) , 8618-21, (2006)

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Abstract

An efficient preparation of pure ethyl Z- and E-alpha,alpha-difluoro-4-phenyl-3-butenoate 1a and 1b together with the corresponding acids 2a and 2b is described. The procedures involve stereocontrolled additions of *CF2CO2Et to phenylacetylene or beta-bromostyrene. Compound 1a is easily obtained by addition of *CF2CO2Et to phenylacetylene via a mechanism where the stereochemistry is controlled by an electron-transfer process to produce predominantly the Z vinyl anion. The product 1b is obtained by *CF2CO2Et addition-elimination to Z- or E-beta-bromostyrenes via a mechanism where the stereochemistry is controlled by steric factors in the conformational equilibration of the intermediates.