Rare-Earth Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes and Subsequent Hydrophosphination in One Pot

Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm), catalyzed regio- and stereoselective
dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in
high yields. The additives played a crucial role to depress the oligomerization and to control the
regio- and stereochemistry of the dimerization. Thus, the selectivity for (Z)-head-to-head enynes
was increased in the order of tertiary < secondary < primary amine additives. On the other hand,
the reversed order was observed for the formation of head-to-tail dimers. When α,ω-diynes were
subjected to the dimerization, very novel cyclic bisenyne compounds were given through double-dimerization in satisfactory yields. In addition, an application of the system allowed subsequent
hydrophosphination of the enynes generated in situ with diphenylphosphine, giving rise to
1-phosphinyl-1,3-dienes as the sole products in excellent yields after oxidative workup.