HIGHLY STEREOSELECTIVE SYNTHESIS OF CONJUGATED POLYENES VIA A HOMOCOUPLING REACTION OF UNSATURATED SILANES

A new method for the synthesis of conjugated polyenes containing up to eight double bonds with all-E configuration is reported. The procedur e is based upon a homocoupling reaction of dienyl-, trienyl-, or tetra enylsilanes, promoted by PdCl2 in methanol and in the presence of LiCl and CuCl2. Configurational and conformational assignments were rigoro usly made on the basis of NMR spectra. The compounds obtained represen t a novel interesting class of symmetrically substituted polyenes with potential optical and electrooptical properties. By changing the solv ent, the homocoupling process can be switched to the halogenation of t he silyl-substituted terminal double bond, thus leading to polyenyl ha lides.