SYNTHESIS OF VARIOUSLY 2-SUBSTITUTED ALKYL (Z)-2-ALKENOATE AND (E)-2-ALKENOATE AND (Z)-ALPHA-YLIDENE-GAMMA-BUTYROLACTONE AND (E)-ALPHA-YLIDENE-GAMMA-BUTYROLACTONE VIA PALLADIUM-MEDIATED CROSS-COUPLING REACTIONS BETWEEN ORGANOSTANNANES AND ORGANIC HALIDES

Stereoisomerically pure trisubstituted alpha,beta-unsaturated esters of general formula 7 have been efficiently synthetized using two different protocols. The first one involves the palladium(0)/copper(I)-mediated cross-coupling reaction between alkyl (E)-2-tributylstannyl-2-alkenoates, (E)-2, and aryl or alkenyl iodides. The second protocol, which allows to prepare stereodefined 2-aryl, 2-methyl, 2-(1-alkenyl) as well as 2-acyl substituted alpha,beta-unsaturated esters, is based on the cross-coupling reaction between easily available alkyl (Z)- or (E)-2-halo-2-alkenoates and organostannanes in NMP, in the presence of catalytic amounts of PdCl2(PhCN)(2), AsPh(3) and CuI. (Z)-and (E)-2-ethenyl substituted alpha,beta-unsaturated esters prepared according to this procedure have been proven to be useful precursors to (Z)- and (E)-alpha-ylidene-gamma-butyrolactones, (Z)- and (E)-8, respectively.