Alkenes from sulfoximines

2-MethyI-l-hexadecene and 4-t-butyI-l-methyIenecyclohexane were obtained respectively in 85 and 73% yields. 

The use of sulfoximines in the syntheses of optically active compounds has been reported [429]. A remarkable ketone methylcnation with optical resolution was realized. A highly selective diastereofacial addition of an enantiopure sulfoximine to a racemic ketone, chromatographic separation of the two diastereoisomers and reductive cleavage yielded both enantiomers of (3-panasinsene [430], isolated from the root of ginseng, a herb used in Chinese folk medicine. 

Other general procedures for carbonyl alkylidenation are based upon the following p-hydroxy sulfur compounds  

These methods were extended to p-hydroxy orthothioesters and p-hydroxy thioacetals [438], leading to ketenethioacetals and vinyl sulfides. With secondary alcohols (R2 - H) a side reaction, which can become preponderant when SOCI2 is used instead of P2I4 in the elimination step, was observed a rearranged product (R2 = SMe in the olefin) was formed. 

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 CHBrj, Zn, TiCl4 and TMEDA (Table 4.4). 

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