PALLADIUM(0)-CATALYZED ADDITION OF ME(3)SNSNME(3) TO ALKYL 2-ALKYNOATES AND N,N-DIMETHYL-2-ALKYNAMIDES - FACILE PREPARATION OF ALKYL (Z)-2,3-BIS(TRIMETHYLSTANNYL)-2-ALKENOATE AND (E)-2,3-BIS(TRIMETHYLSTANNYL)-2-ALKENOATE AND (E)-N,N-DIMETHYL-2,3-BIS(TRIMETHYLSTANNYL)-2-ALKENAMIDES

Treatment (tetrahydrofuran (THF), room temperature or reflux) of the alkyl 2-alkynoates 9-26 with (Me(3)Sn)(2) in the presence of a Pd(0) catalyst ((Ph(3)P)(4)Pd) provides good to excellent yields of the corresponding alkyl (Z)-2,3-bis(trimethylstannyl)-2-alkenoates 47-64. The latter substances are thermally labile and, as demonstrated by a number of examples, are transformed upon heating (75-95 degrees C) into the thermodynamically more stable E isomers. The Pd(0)-catalyzed addition of (Me(3)Sn)(2) to N,N-dimethyl-2-alkynamides 44-46 is quite slow and the initially formed products ((Z)-N,N-dimethyl-2,3-bis(trimethylstannyl)-2-alkenamides) rearrange to the corresponding E isomers at room temperature.