Allylic sulfonyl carbanions synthesis

The preparation of 3,7-dimethyl-2-fra/ij-4-rranj-6-franj-octatrienoic acid (Scheme 62) is a good example of the introduction of a sulfonyl group from sodium sulfinate, of the coupling reaction of a sulfonyl carbanion and allylic bromide and finally of the elimination of the sulfonyl group in basic medium giving the aW-trans compound. The same method was used for vitamin A synthesis (Scheme 63). 

Synthesis of (+)-Chatancin. The alkylation of an a-sulfonyl carbanion derived from a y-alkoxy functionalized sulfone with an allylic bromide and subsequent reductive desulfonylation with Na/Hg constitutes a key step in the synthesis of the marine diterpene (+)-chatancin (Eq. 144).251... 

Synthesis of All-t/a/is-Geranylgeraniol. The type of alkylation described above for the synthesis of bacillariolide III is widely used in the synthesis of natural products due to the mild reaction conditions and high stereospecificity. The formation of the C-C bond takes place when activated a-sulfonyl car-banions derived from (3-ketosul tones, a-sulfonyl sulfones or, less often, allylic sulfones react with the H-allyl palladium complex. In the synthesis of all-trans-geranylgeraniol, the a-sulfonyl carbanion adds to the Ti-allylpalladium complex of 2-(prop-l-en-2-yl)oxirane. Final reductive desulfonylation affords the desired compound, as depicted in Eq. 147.254... 

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