Alkenyl sulfides from thiolesters

Synthesis of alkenyl sulfides and ketencdithioacctals from thiolesters and dithiocarbonatcs 

We have mentioned previously (see Section 3.1) the easy formation of a double bond by sulfoxide pyrolysis. Associated with an alkylative step of a metallated sulfoxide, the sequence is of great value in alkene synthesis [44U, 441], as in the one-pot reaction given here. 

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Another way of synthesis of ketencdithioacetals and of alkenyl sulfides makes use of an alkylidenation of dithiocarbonates or thiolesters with a reagent introduced by Takai [439] and prepared from R CHBr2, Zn, TiCl4 and TMEDA (Table 4.4). 

Alkenes. Titanocene bis(triethyl phosphite), which is prepared in situ from titanocene dichloride, triethylphosphite, and Mg, promotes carbonyl olefmation with gem-dichlorides and dithioacetals [e.g., l,l-bis(phenylthio)cyclobutane ] including those derived from enals (to give 1,3-dienes). Enol ethers-and alkenyl sulfides are obtained in the analogous reaction with dithioorthoformates and trithioorthoformates. Cross-coupling of dithioacetal and thiolesters furnishes predominantly (Z)-alkenyl sulfides. ... 

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