Halohydrins from Tartaric Acids

Diethyl D-tartrate (2b), treated similarly with 30% hydrobromic acid in acetic acid followed by acidic hydrolysis, is converted to diethyl 6 y /fro-(2R,3R)-2-bromo-3-hydroxysuccinate (824) in an overall yield of 73%. Sodium ethoxide cylization affords (2 S, 3 S)-2,3-epoxysuccinate (825), which is the enantiomeric epoxide of 821. Epoxide cleavage with lithium dimethylcuprate provides in 78% yield diethyl (2S,3R)- eo /zro-3-methylmalate (826), which is converted in eight steps to ( —)-(l S, 2 S, 4iS, 5R)-2,4-dimethyl-5-ethyl-6,8-dioxobicyclo-[3.2.1]octane or ( —)-(5-multistriatin (827), one of the eight possible stereoisomeric forms for this pheromone component responsible for the aggregation of the North American 

The ability of non-racemic C2-symmetric aziridines 848 and 849 to undergo rapid nucleophilic ring-opening to provide synthetic equivalents for the j5-cation of aspartic acid illustrates the utility of the azide 822. Treatment of 822 with triphenylphosphine in refluxing benzene results in reduction of the azide to an amine that readily undergoes ring closure to aziridine 845. Subsequent tosylation of the secondary nitrogen affords 848 in 73% yield for the two steps. 

A similar series of reactions utilizing 837 provides the enantiomeric 849 [242], 

Nucleophilic ring-opening of 848 with a variety of nucleophiles occurs with clean inversion to provide the compounds 850 in moderate yields. The C2-symmetric nature of 848 conserves both the stereochemical and enantiomeric purity. Moreover, the two ester groups as well as the tosyl moiety presumably activate the aziridine toward nucleophilic attack [242]. 

The radical debromination of 856, prepared fi om (+ )-dimethyl tartrate (la) as described for 819, with trimethyltin chloride in the presence of AIBN and sodium borohydride in ethanol below 10 °C followed by deacetylation with 3% hydrochloric acid affords (/ )-( + )- 

---