HIGHLY REGIOSELECTIVE AND STEREOSELECTIVE SILYLFORMYLATION OF ALKYNES UNDER MILD CONDITIONS PROMOTED BY DIRHODIUM(II) PERFLUOROBUTYRATE

Addition to alkynes by organosilanes and carbon monoxide to form beta-silylacrylaldehydes (silylformylation) occurs efficiently in the presence of dirhodium(II) perfluorobutrate, Rh2(pfb)4, with turnover numbers that exceed 300. Reactions take place at atmospheric pressure and 0-degrees-C by controlled addition of the alkyne to the combination of organosilane and Rh2(pfb)4 or at 10 atm of CO without this control. Terminal alkynes are directed to silylformylation products in moderate to high yield with complete regiocontrol for carbonylation at the substituted carbon and with exceptional stereocontrol for the Z isomer (>10:1). Preferential silylformylation occurs with triethylsilane in competition with hydrosilylation, and this preference is greatly enhanced with the more reactive dimethylphenylsilane. With internal alkynes hydrosilylation is often dominant. At 1 atm of CO 3-butyn-2-one undergoes trimerization to 1,3,5-triacetylbenzene, and both CO and organosilane in combination with Rh2(pfb)4 are required, but at 10 atm of CO silylformylation occurs to the near exclusion of this trimerization reaction. Similar processes occur with methyl propynoate, but they are complicated by competitive hydrosilylation of the silylformylation product. The active catalyst for silylformylation is generated from Rh2(pfb)4 by CO association followed by hydrosilylation that generates trialkylsilyl perfluorobutyrate.