Cp(2)Ti[P(OEt)(3)](2)-promoted reactions of 2-(alk-1-yn-1-yl)-2-(trialkylsilyl)-1,3-dithianes (RS)(2)C(Si)CCR with terminal olefins and carbonyl compounds produced (trialkylsilylethynyl)cyclopropanes and 1-(trialkylsilyl)alk-3-en-1-ynes, respectively. These compounds were suggest to be produced via the formation of intermediary titanium alpha-(trialkylsilylethynyl)carbene complexes Cp(2)Ti=C(R)CCSi in preference to their regioisomers, alpha-(trialkylsilyl)alkynylcarbene complexes Cp(2)Ti=C(Si)CCR.

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[reaction: see text] The Cp(2)Ti[P(OEt)(3)](2)-promoted reaction of 2-(alk-1-yn-1-yl)-2-(trialkylsilyl)-1,3-dithianes with 1-alkenes regioselectively produced [(trialkylsilyl)ethynyl]cyclopropanes with a formal allylic rearrangement. The reaction of the thioacetals with ketones proceeded with the same regioselectivity to produce 1-(trialkylsilyl)alk-3-en-1-ynes predominantly. It is suggested that these reactions proceed via the formation of titanium alpha-(silylethynyl)carbene complexes Cp(2)Ti=C(R)CCSi in preference to their regioisomers, alpha-silylalkynylcarbene complexes Cp(2)Ti=C(Si)CCR.

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Organo-silicon compounds S 0060Cyclopropanation and Carbonyl Olefination Utilizing 2-(Alk-1-yn-1-yl)-2-(trialkylsilyl)-1,3-dithianes via Regioselective Generation of Titanium Alkynylcarbene Complexes. -Silylated alkynyl thioacetals are found to react with terminal olefins and carbonyl compounds in a highly regioselective manner to afford cyclopropanes of type (III) or conjugated enynes such as (VII) and (XI). Subsequent desilylation provides a convenient route to functionalized terminal alkynes which are useful synthons. -(TAKEDA*, T.; OZAKI, M.; KUROI, S.; TSUBOUCHI, A.; J. Org. Chem. 70 (2005) 11, 4233-4239; Dep. Appl. Chem., Fac. Technol., Tokyo Univ. Agric. Technol., Koganei, Tokyo 184, Japan; Eng.) -Jannicke 43-190