Crown ether catalyzed stereospecific synthesis of Z- and E-stilbenes by Wittig reaction in a solid-liquid two-phases system

Potassium hydroxide and a catalytic amount of 18-crown-6 are used, in alternative to the classical Wittig conditions, to prepare very rapidly and stereoselectively Z- and E-stilbenes. In particular, the use of benzyltriphenylphosphonium iodides always leads to a complete Z-stereospecificity, while benzyldiphenylchlorophosphonium salts give a complete E-stereospecificity. (C) 1996 Elsevier Science Ltd