Sulfoxides, aryl vinyl isomerization

Allyl sulfoxide systems appropriate for a transformation to allylic alcohols can also be generated by other preparative methods, e.g. by isomerization of aryl vinyl sulfoxides. Such an isomerization occurs in connection with a Knoevenagel reaction of (10) with aldehydes leading finally to y-hydroxy-a,3-unsatu-rated systems (11), which can easily be transformed into a,3-unsaturated y-lactones (12 Scheme 17). ... 

Hoffmann has used an isomerization of readily available aryl vinyl sulfoxides, which can be obtained in optically active form, to study the possibility of generating optically active allyl alcohols by employing chirality transfer from sulfur to carbon. While this synthetic route (Scheme 18) to allylic alcohols generally works well and gives good yields, the optical yields which could be obtained are only satisfactory in some cases, e.g. (/ )-(Z)-sulfoxide (13) gave the (S)-(+)-octenol (14) with greater than 80% optical purity, whereas the (/ )-( 5-isomer (15) yielded only 29% of the (f )-(-)-enantiomer (16 Scheme 19). 

Chiral vinyl sulfoxides have been prepared by a Wittig Horner reaction of chiral (R)- or (.Si-dimethyl (4-tolylsulfinyl)methanephosphonate with carbonyl compounds3-66,67. For acyclic systems reprotonation of the anions from vinyl sulfoxides gave a mixture of E- and Z-isomers3, whereas isomerization of an exocyclic double bond in a ring system provided access to chiral aryl 1-cycloalkenylmethyl sulfoxides66-67. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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