A NOVEL AND EFFICIENT METHOD TO PREPARE 3-(HETERO)ARYL-1-PROPYNES AND ITS APPLICATION TO THE STEREOSELECTIVE SYNTHESIS OF (2E,4E)-N-(2-METHYLPROPYL)-6-(2-METHYLPROPYL)-6-(2-THIENYL)-2,4-HEXADIENAMIDE, PIPEROVATINE AND (E)-N-(2-METHYLPROPYL)-6-(4-METHOXYPHENYL)-4-HEXYN-2-ENAMIDE

Chemically pure 3-(hetero)aryl-1-propynes, 13, have been prepared in high overall yields by a novel method which involves: (a) a copper(I)-mediated cross-coupling between a halomethyl(hetero)arene, 16, and trimethylsilethynylmagnesium bromide, 17, to give a trimethylsilyl-3-(hetero)aryl-1-propyne, 18; (b) removal of the trimethylsilyl group from 18 by treatment with potassium fluoride dihydrate in DMF. One of these 1-alkynes, i.e. 3-(2-thienyl)-1-propyne, 13a, has been employed in the key step of a highly stereoselective synthesis of naturally-occurring (2E,4E)-N-(2-methylpropyl)-6-(2-thienyl)-2,4-hexadienamide, 6. On the other hand, 3-(4-methoxyphenyl)-1-propyne, 13b, has been used either in two stereoselective syntheses of another natural N-(2-methylpropyl) amide, i.e. piperovatine, 7, or in the preparation of a structural analogue of 7, i.e. (E)-N-(2-methylpropyl)-6-(4-methoxyphenyl)-4-hexyn-2-enamide, 15.