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Titanocene(II)-promoted ring-closing metathesis of the titanium carbene complexes prepared from [2,2-bis(phenylthio)ethyl](but-3-enyloxy)dimethylsilanes or dimethyl(prop-2-enyl)silyl ethers of 3,3-bis(phenythio)propanols gave seven- [a] 155 membered cyclic unsaturated silyl ethers. Oxidative cleavage of a silicon−carbon bond of the cyclic silyl ethers resulted in olefinic diols, with high Z stereoselectivity. silyl ethers of 3,3-bis(phenythio)propanols 5 (Route B). For the preparation of trisubstituted olefins, these two types of cyclization are complementary to each other (Scheme 1).

Titanocene(II)-promoted ring-closing metathesis of the titanium carbene complexes prepared from [2,2-bis(phenylthio)-ethyl](but-3-enyloxy)dimethylsilanes or dimethyl(prop-2-enyl)silyl ethers of 3,3-bis(phenythio)propanols gave seven-

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Preparation of (Z)-Alk-2-ene-1,5-diols by the Titanocene(II)-Promoted Cyclization of Thioacetals Possessing a Terminal Carbon-Carbon Double Bond.-The present new method to prepare olefinic diols with high Z stereoselectivity consists of two reaction steps. First, cyclic unsaturated silyl ether intermediates are formed by a titanocene(II)-promoted ring-closing metathesis of titanium carbene complexes prepared from homoallyl alcohols or 3,3-bis(phenylthio)propanols as starting materials.Oxidative cleavage of a silicon-carbon bond of the cyclic silyl ethers results in formation of the desired title compounds. -(FUJIWARA, TOORU; YANAI, KENJIROU; SHIMANE, KEIKO; TAKAMORI, MAYUMI; TAKEDA, TAKESHI; Eur. J.