Sulphoxides alkynyl

Alkynyl sulphoxides 553, 554 also behave as Michael acceptors and afford the corresponding jS-substituted vinyl sulphoxides upon treatment with nucleo-philes605,644-646 (equations 352 and 353). 

Successive [2,3]- and [3,3]-sigmatropic rearrangements are involved in conversion of the alkynyl sulphoxide (250) into the dihydrobenzothiophen (251). Basic conditions rearrange (251) to (252). ... 

The catalysed -elimination of hydrogen bromide from 2-bromoethyl and 1,2-dibromoethyl sulphides, using 9.1.1 or 9.1.2, provides a convenient route to vinyl and alkynyl sulphides, respectively [17, 18], which, as their sulphoxides or sulphones, have considerable utility as dienophiles. Aryl vinyl ethers (>90%) have been obtained by analogous procedures from 2-chloroethyl ethers [19]. 

In view of their importance in asymmetric synthesis new routes have been developed to chiral sulphoxides and related species. Sulphinates, useful as precursors of chiral sulphoxides, have been prepared in 40-70% enantiomeric excess and the synthesis and dieno-philic properties of the isomeric sulphinyl acrylates (2l8) and (219) (Ar = 4-MeCgH ) have been described. ( )-Vinyl sulphoxides have been prepared in high optical purity via 1-alkynyl... 

Unsaturated Sulphoxides.—Addition of an alkynyl-lithium to an organo-borane R3B gives (RJBC CR )Li, which with methanesulphinyl chloride gives an unstable vinyl sulphoxide RlBCR =CR SOMe, which gives the alkyne R C CR the net result being the anti-Markownikov reductive alkynylation of an alkene, since RsB is prepared by hydroboration of an alkene. ... 

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