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Cationic rhodium complex-catalysed hydrosilylation of alk-l-ynols including propynylic alcohols with triethylsilane is highly selective to give (a-l -triethylsilyl alk-1 -enols as products in excellent yields.Neutral rhodium complex-catalysed hydrosilylation of alk-lynes gives (2)-vinylsilanes as the major product via the trans addition of Si-H across the carbon-carbon triple bond.1 In contrast to the extensive amount of the work on the neutral rhodium complex-catalysed hydrosilylation of alk-l-ynes, catalysis by cationic rhodium complexes has not been reported. In the course of the study of solvent effects on hydrosilylation, we noticed reversal of stereoselectivity for cationic rhodium complex catalysis, i. e. cationic rhodium complex-catalysed hydrosilylation of hex-l-yne with triethyl-

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Alkynyl propargyl sulfides underwent [3,3] sigmatropic rearrangement followed by ring closure to afford isolable 4-methylenecyclobutenethiones, and an intermediary allenylthioketene 2 was isolated by heating t-butyldimethylsilylethynyl propargyl sulfide.

Cyclobutane derivatives Q 0022Isolation and Characterization of an Allenylthioketene and 4-Methylenecyclobutenethiones Generated by Thermal Reaction of Alkynyl Propargyl Sulfides.-Alkynyl propargyl sulfides (I) undergo thermally induced [3,3] sigmatropic rearrangement followed by ring closure to afford 4-methylenecyclobutenethiones (III). Similar thermal reaction of alkynyl propargyl sulfide (VII) stops at the formation of relatively stable allenylthioketone (VIII). Studies on the reactivity of both types of reaction products round off the report. -(AOYAGI*, S.; SUGIMURA, K.; KANNO, N.; WATANABE, D.; SHIMADA, K.; TAKIKAWA, Y.; Chem. Lett. 35 (2006) 9, 992-993; Dep. Chem. Eng., Fac. Eng., Iwate Univ., Ueda, Morioka 020, Japan; Eng.) -R. Langenstrassen 05-059