A new method for the synthesis of conjugated polyenes containing up to eight double bonds with all-E configuration is reported. The procedure is based upon a homocoupling reaction of dienyl-, trienyl-, or tetraenylsilanes, promoted by PdCl(2) in methanol and in the presence of LiCl and CuCl(2). Configurational and conformational assignments were rigorously made on the basis of NMR spectra. The compounds obtained represent a novel interesting class of symmetrically substituted polyenes with potential optical and electrooptical properties. By changing the solvent, the homocoupling process can be switched to the halogenation of the silyl-substituted terminal double bond, thus leading to polyenyl halides.

1997ketones ketones (benzene compounds) Q 0350 -122Highly Stereoselective Synthesis of Conjugated Polyenes via a Homocoupling Reaction of Unsaturated Silanes.-A new method for the synthesis of all-E configurated polyenes by Pd-catalyzed homocoupling of silanes (I), prepared using known procedures, is presented with a view to developing molecular-electronic devices. Changing the solvent permits the exchange of the silyl group for a halogen atom. The polyenyl halides are useful intermediates in the synthesis of extended conjugated systems by cross-coupling reactions. -(BABUDRI, F.; CICCIOMESSERE, A. R.; FARINOLA, G. M.; FIANDANESE, V.; MARCHESE, G.; MUSIO, R.; NASO, F.; SCIACOVELLI, O.; J.

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