2-Sulfinyl-2-alkenolides

In contrast to a, -ethylenic ketones or even a, -ethylenic sulfones, a, ) -ethylenic sulfoxides generally are not sufficiently electrophilic to undergo successful nucleophilic j8-addition . a-Carbonyl-a, j8-ethylenic sulfoxides, however, are potent, doubly activated alkenes which undergo rapid and complete -addition of various types of nucleophiles even at — 78 °C. A brief account summarizing this area is available . The stereochemical outcome of such asymmetric conjugate additions to enantiomerically pure 2-sulfmyl 2-cycloalkenones and 2-sulfinyl-2-alkenolides has been rationalized in terms of a metal-chelated intermediate in which a metal ion locks the -carbonyl sulfoxide into a rigid conformation (36 cf. 33). In this fixed conformation, one diastereoface of the cyclic n... 

Since early investigations about the asymmetric addition of diethyl sodiomalonate to optically active vinylic sulfoxides,100-101 Posner and his coworkers102-117 have developed a highly useful methodology based on the conjugate addition of carbon nucleophiles to homochiral a-arylsulfinyl-a,(J-unsaturated carbonyl compounds. While acyclic derivatives still lead only to moderate results,103 the strength of this method is for cyclic systems. For example, the 2-sulfinyl-2-cycloalkenones (94) and (95), the 2-sulfinyl-2-alkenolides (96) and (97), as well as their respective enantiomers are excellent substrates. All these compounds are quite readily accessible in enantiomeric purities of >98% and are configurationally stable, at least for several months at 0 C. 

Asymmetric Synthesis of Carbon-Cartxin Bonds Using Sulfinyl Cycloalkenones, Alkenolids and Pyrones"... 

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