AN EASY ACCESS TO TRISUBSTITUTED VINYL CHLORIDES AND IMPROVED SYNTHESIS OF CHLORO BROMOSTILBENES/

The alpha-chlorophosphonates (OCH2CMe2CH2O)P(O)CHCl-C6H4-4-R [R=H (4), Me (5), OMe (6)], which are now readily accessible, react with ketone s R'C(O)R '' in the presence of NaH (without recourse to the more expe nsive t-BuLi) to afford trisubstituted vinyl halides R'C(R '')=CCl(C6H 4-4-R) in good yields. The corresponding alpha-bromophosphonates [R=H (7); Me (8)] failed to react with ketones and gave the symmetrical ace tylenes 4-R-C6H4-C=C-C-6-H-4-4-R as isolable products in low yield. We have found that K2CO3 in refluxing xylene is a good base for the synt hesis of chlorostilbenes; using this base the bromostilbenes ArCH=CBr( C6H4-4-R) can be prepared in significantly higher yields than by using NaH. The stereochemistry of two of the trisubstituted vinyl chlorides is unambiguously proven by X-ray structure determination. Thus for (C l)PhC=CPh(Me), the isomer with the upfield NMR shift for the CH3 proto ns and for (Cl)PhC=C(Ph)(C6H4-4-Me), the isomer with the downfield NMR shift for the -C6H4-4-CH3 protons have Z stereochemistry. (C) 1998 El sevier Science Ltd. All rights reserved.