PALLADIUM-CATALYZED AND MOLYBDENUM-CATALYZED HYDROSTANNATION OF ALKYNES - A NOVEL ACCESS TO REGIODEFINED AND STEREODEFINED VINYLSTANNANES

In the presence of catalytic amounts of dichlorobis(triphenylphosphine)palladium or of the π-allylmolybdenum complex 3, tributyltin hydride adds instantaneously at room temperature to various alkynes to give the corresponding vinylstannanes in good to excellent yields. The reaction is totally stereoselective (cis addition). With mono-alkylacetylenes RC=CH, good regioselectivity for the formation of l-(tributylstannyl)alkenes (vs 2-(tributylstannyl)alkenes) is attained only if the R substituent is sufficiently bulky. The molybdenum-catalyzed hydrostannation of (trimethylsilyl)acetylene gives l-(tributylstannyl)-l-(trimethylsilyl)ethene with 85% selectivity. The palladium-catalyzed hydrostannation of 1-chloro-l-octyne regio- and stereoselectively yields (-l-chloro-l-(tributylstannyl)octene, which, on reaction with I2 or Br2, leads to the corresponding 1-chloro-l-halo-l-octenes with total conservation of stereochemistry. 1-Bromo-l-alkynes behave differently from their chloro analoguers, reacting with 2 equiv of tributyltin hydride to give CE)-l-(tributylstannyl)-l-alkenes. Conjugated alkynones or alkynoic esters generally yield CE)-a-(tributylstannyl)enones and enoates esters which are important synthons in organic chemistry. Symmetrically substituted internal conjugated diynes, 1,3-diynes and l-(trimethylsilyl)-l,3-diynes give a single monohydrostannation product with total chemo-, regio-, and stereoselectivity. © 1990, American Chemical Society. All rights reserved.