T/ireo-isomer

Diastereoselective hydrogenation of vinyl sulfones and sulfoxides. Hydrogenation of the vinyl sulfone 2 with the Rh catalyst 1 proceeds in 99% de to give 3. Similar hydrogenation of the corresponding sulfoxide provides 5, which on perborate oxidation gives the t/ireo-isomer of 3. Apparently the steric course of hydrogen-... 

In the second approach, a chiral nitrogen-containing compound has most often been used as the ligand to achieve enantioselectivity. Thus, oxidation of ( )- tilbene (22 equation 9) with a stoichiometric quantity of osmium tetroxide in toluene at room temperature, in the presence of dihydroquinine acetate (23), yielded t/ireo-hydrobenzoins (24) after reductive hydrolysis, with an enantiomeric excess of 83.2% in favor of the (lS,2S)-(-)-isomer performing die reaction at -78 C increased the enantiomeric excess to 89.7%. 

The mechanism of cleavage by periodate is consistent with a cyclic, five-membeied ring intermediate (10) shown in Scheme 6. Support comes from the fact that the cis isomers of cyclic diols are more reactive than the trans isomers, t/ireo-l,2-diols undergo oxidation faster than the erythro isomers and the inert behavior of diaxial fra j-l,2-diols which cannot form a cyclic periodate ester. ... 

A mixture of DL-tosylserine and L( + )-f/ireo-l-p-nitrophenyl-2-amino-l,3-pro-panediol dissolved in water by heating at 85-90, allowed to stand 24 hrs. at room temp., and the resulting diastereomeric salts treated with HCl (+) tosylserine and (—)-tosylserine (Y 95%), the latter dissolved in 12%-NaOH and refluxed 24 hrs. DL-tosylserine (Y ca. 85%). L(+)-fiireo-l-p-Nitrophenyl-2-amino-1,3-propanediol is readily available and inexpensive. By the above sequence, racemates can be converted into one antipode. Also resolution by fractional crystallization of racemates in the presence of a slight excess of one isomer s. T. Perlotto and M. Vignolo, Farmaco, Ed. Sci. 21, 30 (1966). 

D-t/ reo-butane-2,3-diol L-i/ireo-butane-2,3-diol 8-30, butane-2,3-diol isomers... 

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