A variety of tantalum-alkyne complexes are generated in situ by treatment of alkynes with low-valent tantalum derived from TaC& and zinc. These complexes add regioselectively to carbonyl compounds in a one-to-one fashion to yield (E)-allylic alcohols stereoselectively. Iodinolysis of the oxatantalacyclopentene, which is postulated as an intermediate of the reaction, gives a (Z)-3-iodo-2-propen-l-ol derivative. In contrast to tantalum-alkyne ...
