Sulphinate group, elimination

Allyl sulphones can be converted to dienes by alkylation and elimination of sulphinic acid under basic conditions (equation 64)105. Several vitamin A related polyenes have been synthesized following this two-step protocol (Table 10)106. The poor leaving-group ability of the arylsulphonyl group requires treatment with strong base for elimination. However, elimination of the allylsulphonyl group takes place readily under palladium catalysis (equation 65)107. Vinyl sulphones can be converted to dienes via Michael addition, alkylation with allyl halides and elimination of sulphinic acid sequence (equation 66)108. 

Backvall and Juntunen and Fuchs and Braish have developed ( )-2-phenylsuphonyl-1,3-dienes prepared under Julia conditions as versatile synthones for a variety of organic transformations . These dienes undergo facile Diels-Alder reaction and subsequent 1,4-elimination of sulphinic acid by base to generate a new diene (equation 62) . An elegant extension of this method is to use chiral sulhnylmaleate which, on Diels-Alder reaction and elimination of the sulhnyl group, generates an optically active diene for further applications (equation 63) . 

After the elimination, the water-soluble sulphinates can be readily recovered, in contrast to the Wittig reaction which suffers from the difficulty of recycling phosphine oxide. Modifications of the Julia olefination lead to more general routes to a variety of carotenoids. The success of this method is attributable to improvement of the reductive cleavage of the sulphonyl group by reduction with dithionites [29]. 

Elimination of sulphur dioxide from an S-bonded sulphinate complex is a process related to sulphur dioxide insertion. Kinetic studies on the rearrangement of the five-co-ordinate sulphinato-complexes (20) to the sulphur dioxide complexes (21) show that if the organic group R contains electron-withdrawing... 

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