R - -3- p-Tolylsulfinyl propionic Acid

Aldol-iype Condensation. Dimetalation of (R)-(+)-3-(p-tolylsulfinyl)propionic acid with Lithium Diisopropylamide produces a chiral homoenolate dianion equivalent which reacts with carbonyl compounds to afford p-sulfinyl-y-hydroxy acids these spontaneously cyclize to give the corresponding p-sulfinyl 7-lactones (eq 2)  

The condensation of the dilithio derivative of (R)-(+)-3-(p-tolylsulfinyl)propionic acid with protected glycoaldehy-des (O-r-butyl and 0-benzyl) gives 5-alkoxy-4-hydroxy-3-(p-tolylsulfinyl)pentanoic acids, which spontaneously cyclize to the corresponding 3-sulfinyl-4-alkoxymethyl butanolides (eq 4). Pure diastereomers can be separated by flash chromatography and are obtained in comparable amounts. The corresponding optically pure butenolides are obtained by pyrolytic elimination of the sulfoxides and then transformed into natural (-i-)-(/ )-umbelactone (eq5). 

Two new chiral carbon atoms are formed in the condensation and four diastereoisomeric p-sulfinyl y-lactones can therefore in principle be obtained. However, only two dia-stereoisomers, (3S,4, s ) and (3R,4S,Rs), are isolated when the carbanion is condensed with pivalic aldehyde, benzaldehyde, or pinacolone (yield 65-70% for aldehydes, ratio 53 47 yield 47% for pinacolone, ratio 81 19). The diastereoselectivity decreases when the two substituents of the carbonyl group are sterically similar. However, single diastereoisomers can easily be separated through chromatography and transformed in high yield into both enantiomers of optically pure saturated (by desulfurization) and a,(3-unsaturated y-lactones (by pyrolytic sulfoxide elimination) (eq 3). The relative and absolute stereochemistry of all the products have been determined by circular dichroism, nuclear Over-hauser effects, and X-ray analyses. 

Carrera, P Resnati, G. Ticozzi, C. Chem. Commun./J. Chem. Soc., Chem. Commun. 1984, 19. 

P Resnati, G. Viani, F, Garz. Chim. Ital. 1987, 117, 747. 

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Papageorgiou and Benezra204 treated chiral r-butyl (-)-(S)- and ( + )-(R)-2-(p-tolylsulfinyl)propionate with an aldehyde, then pyrolyzed the mixture and obtained chiral a-(hydroxyalkyl)acrylate in 75% e.e. Similarly, condensation of the anion of ( + )-(R)-3-(p-tolylsulfinyl)propionic acid 159 with aldehydes was found to give the diastereomeric [i-sulfinyl-y-lactones, (+)-(Sc4,Rc5,Ps)-160a and ( + )-( c4,Sc5,l s)-160b in an approximate ratio of 60 40205. 

Butenolides 1 -Chloro-N,N-trimethylpro-penylamine. Cyclopropenone 1,3-propane-diyl ketal. Peracetic acid. Silver carbon-ate-Celite. (R)-( + )-3-(p-Tolylsulfinyl)-propionic acid. 

Reaction of the a-carbanion of an alkyl aryl sulfoxide (RCH2SOAr) with aldehydes may give four dia-stereomers. In general, the reaction is highly diastereoselective with respect to the a-sulfinyl carbon, but poorly diastereofacially selective with respect to attack on the caibonyl component. In fact, the a-carbanion (31) of benzyl r-butyl sulfoxide adds to an aldehyde to produce only two diastereomers (32a) and (32b). As shown in Scheme 10, the selectivity increases when the counterion is Zn. A transition state structure (33) is proposed to account for the anti stereoselection. Addition of the dianion of (R)-3-(p-to-lylsulfinyl)propionic acid (34) to aldehydes affords two main diastereoisomeric -(p-tolylsulfinyl)-7-lac-tones (35 R = Ph and Bu. ca. 60 40). These isomers (35) were separated by chromatography, and their... 

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