Palladium(0)-catalyzed addition of Me3SnSnMe3 to alkyl 2-alkynoates and N,N-dimethyl-2-alkynamides. Facile preparation of alkyl (Z)- and (E)-2,3-bis(trimethylstannyl)-2-alkenoates and (E)-N,N-dimethyl-2,3-bis(trimethylstannyl)-2-alkenamides

Abstract

Treatment (tetrahydrofuran (THF), room temperature or reflux) of the alkyl 2-alkynoates 9–26 with (Me3Sn)2 in the presence of a Pd(0) catalyst ((Ph3P)4Pd) 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 °C) into the thermodynamically more stable E isomers. The Pd(0)-catalyzed addition of (Me3Sn)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.