1.2- Diphenylethane-l,2-diol

The chiral substrate trans- stilbene oxide (10.121) behaved differently, yielding meso-l,2-diphenylethane-l,2-diol (meso-10.122) [183], This means that, in both enantiomeric substrates, the enzyme does not discriminate between the two oxirane C-atoms, bringing about inversion of configuration at the C-atom attacked. Interestingly, the various stereoisomers of 1,2-diphenylethane-l, 2-diol can be interconverted metabolically by alcohol/ketone equilibria catalyzed by alcohol dehydrogenases. 

Ole/m synthesis, Eastwood ei al. have reported a new method for conversion of W -diols into alkenes. For example, rut-1,2-diphenylethane-l,2-diol (1) is heated with N,N-dimcthylformamide dimethyl acetal to give 2-dimethylamino-/rani -4.5-diphenyl-1,.3-dioxolanc (2). When this dioxolane is heated with acetic anhydride at 165-180° rruns-stilbene (3) is formed in 80% yield. Similarly, meso-l,2-diphenylethane-l,2-diol is converted into m-stilbene (75%) and a trace of truns-stilbene if the elimination... 

The reaction of butyllithium with 1-naphthaldehyde cyclohexylimine in the presence of (/C )-l,2-diphenylethane-1,2-diol dimethyl ether in toluene at —78 °C, followed by treatment with acetate buffer, gave 2-butyl-1,2-dihydronaphthalene-l-carbaldehyde, which was then reduced with sodium borohydride in methanol to afford (1 R,2.S)-2-butyl-1 -hydroxymcthyl-1,2-dihydronaphthalene in 80% overall yield with 91 % ee83. Similarly, the enantioselective conjugate addition of organolithium reagents to several a,/J-unsaturated aldimines took place in the presence of C2-symmetric chiral diethers, such as (/, / )-1,2-butanediol dimethyl ether and (/, / )- ,2-diphenylethane-1,2-diol dimethyl ether. 

Fig. 10.28. The stereochemistry of enzymatic hydrolysis of stilbene oxide. The achiral (meso) r/.v-sli Ibene oxide (10.7) yields only one of the two enantiomers of IhreoA,2-diphcnylethane-1,2-diol (10.122). In contrast, the chiral trans-stilbene oxide (10.121) is hydrated exclusively to meso-l -diphenylethane-l -diol [182][183]. 

Treatment of benzaldehyde with TiCU (lequiv.) and magnesium (l.Sequiv.) in TFIE at 25°C for 30min gives a mixture of 1,2-diphenylethene (43% yield) and dl- and OT ro-l,2-diphenylethane-l,2-diols (29% combined yields, dljmeso = AZiS ). The reaction conducted at 80°C produces the diphenylethene in 62% yield selectively. However, when catechol (1 equiv.) is added to the reaction mixture, pinacols are produced selectively in 76% yield dljmeso = 54/46) even at 80 °C. " Ultrasonic irradiation of a mixture of TiCU (15% in dilute HCl solution, 2 equiv.) and magnesium (4 equiv.) in EtOH accelerates the pincaol formation, but the diastereomeric ratio remains at a low level (dljmeso = 68/32). ... 

Treatment of 1,3,2-dioxathiolane. 7,.7-dioxides with telluride ion, generated in situ by reduction of the elemental Te, yields alkenes rapidly (10min-2h) under mild conditions (0°C to rt) <1995TL7209>. The reduction may be performed with 0.1 equiv or less of Te in the presence of a stoichiometric amount of LiEt3BH or NaH. The reaction is stereospecific, for example, / >-2,3-diphenylethane-2,3-diol produces ar-stilbene, and d,l-2,3-diphenylethane-2,3-diol gives trans-stilbene. The sulfates of m-diols are readily converted to ar-alkenes, as shown in Equation (12) <1995TL7209>. 

The enantiomers of thiochroman 1-oxide have been obtained by oxidation of thiochroman in the presence of (R,R)-l,2-diphenylethane-l,2-diol (DPED) or L-diethyl tartrate. In the case of the enantioselective oxidation of thiochroman-4-one, (R,R)-DPED and (V,V)-DPED were used as the chiral inducers <2002CH400>. Fligh yields of both (—)-(R)-thiochroman 1-oxide and (—)-(R)-thiochroman-4-one 1-oxide and with enantioselectivities of 98% and 96%, respectively result from the reaction of H202 with the heterocycles when significant amounts of chloroperox-idase are used as catalyst <1998CH246>. 

Photocatalytic cleavage of 1,2-dioIs [117] or l,2-diphenylethane-l,2-diols [118] with Fe" porphyrin (Fe " (tmpyp)) leads to aldehydes and small quantities of the corresponding acids (eq. (16)). 

Included in this class of olefins is ( )-stilbene (entry 20), which throughout studies of AD has usually been the olefin dihydroxylated with the highest degree of enantioselectivity. Availability of (RJi) or (5, l,2-diphenyl-l,2-etlianediol (also referred to as stilbenediol or dihydrobenzoin) with high enantiomeric purities has led to reports of a number of tqrplications, including incorporation irito chiral dioxaphospholanes [50], chiral boronates [51], chiral ketene acetals [52], chiral crown ethers [53], and conversion into 1,2-diphenylethane-1,2-diamines [54]. Dihydroxylation of the substituted fraru-stilbene 46 with OSO4/NMO and DHQD-CLB gives the / ,/f-diol 47 with 82% ee in 88% yield [55]. 

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