Enantioselective synthesis sulfone conjugates

The Schollkopf nucleophile was also used in the enantioselective synthesis of -methyl-tryptophan. In this case the dihydropyrazine nucleophile undergoes conjugate addition to the sulfone 35a, which yields afl -methyltryptophan after reductive desulfonylation and hydrolysis <95JOC4978>... 

The enantioselective synthesis of (-)-sedacryptine, a piperidine alkaloid, has been achieved via the double intramolecular conjugate addition of a carbamate group onto a vinyl sulfone and then an enone (Scheme 30). The first conjugate addition of 108 proceeded in a. syn-1,3 fashion. The successive cyclization of the resulting carbamate anion 110, which was formed from carbanion 109 via proton transfer, gave a mixture of stereoisomeric products 111 and 112. Both of these isomers were converted into the target natural product.76... 

Haseltine has described an enantioselective formal synthesis of pancratistatin in which the stereocontrol is driven by the aeetonide of conduritol A. The enantioselective hydrolysis (desymmetrization) of this compound was achieved with a lipase, and the aryl-cyclohexane ring bond was formed through an intramolecular cyclization of the activated benzene ring with an allylic triflate (278). Plumet reported a total synthesis of (-l-)-7-deoxypaneratistatin based on the conjugate addition of an aryl-lithium species to a bicyclic conjugated sulfone derived from furan, which enabled the efficient installation of the six stereogenic centers of the cyclohexane ring (279) (Scheme 13). 

Some years later, further developments by Alexakis et al. have shown that prolinol derivative 22a (10 mol%) is a better catalysts for the reaction [89]. The results vary from good, for conjugate addition of linear aldehydes to l,l-bis(benzenesulfonyl) ethylene (77-90% yields 76-93% ee), to moderate (12-91% ee) when using a-branched aldehydes as nucleophiles. Catalyst 22a has been also used by Palomo et al. for the enantioselective conjugate addition of linear and 3-branched aldehydes to E-a-ethoxycarbonyl vinyl sulfones and -a-cyano vinyl sulfones [90], derivatives that after further transformations, which usually involve a reductive desulfonylation process [91], have made possible the synthesis of different interesting chiral building blocks. 

On the other hand, the enantioselective conjugate addition of a-substituted cyano-acetates and cyanoketones to a,P-unsaturated sulfones has been reported by Deng et al. using bifunctional cupreine 127 as catalyst [270]. Substoichiometric amounts of 127 (20 mol%) catalyze the synthesis of chiral sulfones containing all-carbon... 

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