A novel protocol for the stereoselective synthesis of variously substituted (Z)-5-ylidene-5H-furan-2-ones

The Pd(II)- or Ag(I)-catalyzed lactonization of easily available (E)-4- (1-alkynyl)-2-bromopropenoic acids provides (Z)-3-bromo-5-ylidene-5H-furan- 2-ones, 5. These compounds, which represent an unpreviously reported class of (Z)-alkylidenebutenolides, are able to undergo Pd-catalyzed cross-coupling reactions with arylzinc halides, tetraalkylstannanes or alkenylstannanes to provide the corresponding 3-substituted (Z)-5-ylidene-5H-furan-2-ones, 1. The new procedure for the preparation of compounds 1 has been employed in a new synthesis of the butter flavour component bovolide.