LEWIS ACID-CATALYZED HYDROSTANNATION OF ACETYLENES - REGIOSELECTIVE AND STEREOSELECTIVE TRANS-ADDITION OF TRIBUTYLTIN HYDRIDE AND DIBUTYLTIN DIHYDRIDE

Lewis acids such as ZrCl4 or HfCl4 catalyze the hydrostannation of ace tylenes 1 by tributyltin hydride to produce the cis vinylstannanes 2 b y regio- and stereoselective anti-hydrostannation. The hydrostannation of acetylenes using dibutyltin dihydride was also catalyzed by ZrCl4 to give the stereodefined Z-Z divinyltin derivatives 4 by an anti-hydr ostannation pathway. The use of nonpolar solvents such as toluene or h exane was essential for obtaining high stereoselectivity and chemical yield. Since ZrCl4 and HfCl4 are not soluble in such solvents, the hyd rostannations were carried out in a heterogeneous system. The reaction s of internal acetylenes with Bu(3)SnH proceeded smoothly, although th e use of stoichiometric amounts of ZrCl4 gave better results. The ZrCl 4- catalyzed hydrostannation at 0 degrees C gave better yields and ste reoselectivities than the reaction at room temperature. To help clalif y the reason, the reaction of Bu(3)SnH with ZrCl4 was monitored by H-1 and Sn-119 NMR spectroscopy, and it was found that Bu(3)SnH reacted w ith ZrCl4 at room temperature to afford a mixture of tributyltin hydri de, dibutyltin dihydride, and tetrabutyltin.