Diastereomerically selective sulfoxide

Selective or preferential extraction of diastereomeric salts formed from sulfoxide carboxylic acids and alkaloids in water relative to the reciprocal diastereomeric salts has been studied33. 

Figure 32.22 shows the diastereoselective hydrogenation of (R)-/ -keto sulfoxides with Meo-BIPHEP-Ru catalysts [72]. The R chiral center of the substrate matches with the S catalyst, giving the S,R alcohols in >99 1 selectivity, whereas reactions with the R catalyst affords a 6 94 to 10 90 mixture of the S,R and R,R diastereomeric alcohols. The diastereoselection is controlled mainly by the configuration of the catalyst. 

The reaction of 60 with an excess of alkane- or arenesulfinyl chloride affords sulfinate esters 61-(R) and 61-fSj in good yields and moderate selectivity [(4-10) 1]. The diastereomeric sulfinates were separated either by crystallization or by column chromatography. Two arene- and two alkanesulfinates were prepared optically pure by the reported method (Scheme 18). The major isomer of the methanesulfinate was used in the synthesis of o.p. (R) methyl p-tolyl sulfoxide 62 in 76% yield, while the p-toluenesulfinate was used to obtain the (S)-p-phenoxyphenyl p-tolyl sulfoxide 63 in 70% yield. 

Pradilla et al. have shown that simple p-tolyl vinyl sulfoxides undergo nucleophilic epoxidation with metal alkyl peroxides to give enantiopure sulfinyl oxiranes.138 This process takes place with fair to excellent diastereoselectivities. The same group recently reported the epoxidation of diastereomeric hydroxy vinyl sulfoxides, bearing an additional stereocenter adjacent to the reactive carbon-carbon double bond. Hydroxy vinyl sulfoxides 256 and 258 underwent epoxidation with lithium ferf-butyl peroxide with high anti selectivity. However, when potassium ferf-butyl peroxide was used, only hydroxy vinyl sulfoxide 256 showed anti... 

The Uemura system found appHcation in an approach by Hutton towards members of the ustiloxin family of cycHc peptides. While the oxidation employing DET as ligand showed only Httle selectivity, the desired sulfoxide was obtained with a diastereomeric ratio of greater than 50 1 by changing to the (R)-BINOL ligand [23]. 

In 1973 Tsuchihashi reported asymmetric induction during carbon-carbon bond formation between nucleophilic malonate and electrophilic enantiomerically pure styryl sulfoxide 2, producing intermediate diastereomeric carbanions 3a and 3fe (eq 2) (J) Selective formation of diastereomer 2 this irreversible, kinetically controlled addition was rationalized in terms of the preference for an a-sulfinyl carbanion to have the carbon lone-pair orbital trans to the sulfinyl oxygen orbital in a polar solvent. 

Vinyl sulfoxide isomerization followed by Mislow-Evans rearrangement was also central to a S5mthetic route toward the hydroazulene moiety of the antibiotic fungal metabolite guanacastepene A fScheme 18.611. In this case, a diastereomeric mixture of vinyl sulfoxides 241 resulted upon oxidation of the starting vinyl sulfide 240. Subsequent treatment with DBU led to the sequential isomerization/[2,31-rearrangement process. Under these conditions, the intermediate sulfenate was converted to the allylic alcohol 242, produced as a 4 1 mixture of epimers. Here, the modest selectivity in formation of the allylic stereocenter was of no synthetic consequence, as the alcohol was subsequendy oxidized to the corresponding enone. Notably, the overall conversion from 240 to 242 represents a 1,3-vinyl-to-allyl heteroatom transposition. 

Trioses to Hexoses.- A kinetic analysis of the formose reaction has led to the conclusion that the carbonyl rearrangement and retro-aldol reaction steps play a substantial role in the autocatalytic process. The condensation of D-glyceraldehyde acetonide with racemic alkyl (alkylthiomethyl) sulfoxides proceeded with high selectivity to produce diastereomeric l-alkylsulfinyl-l-alkylthio-3,4-0-isopropylidene-D-tetroses with a predominance of e/yrhro-products. An example is given in... 

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