Dihydrobenzoin

The known property of diorganyl tellurides of reducing metallic salts, applied to tita-nium(IV) chloride, generates a titanium(III) species which is a useful reagent for some selective reductions. By this method benzaldehyde is reduced to dihydrobenzoin, and benzyl to benzoin, and successively to desoxybenzoin. ... 

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 (R,R) or (.5,5)-1,2-diphenyl-1,2-ethanediol (also referred to as stilbenediol or dihydrobenzoin) with high enantiomeric purities has led to reports of a number of applications, including incorporation into 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 rran.r-stilbene 46 with Os04/NMO and DHQD-CLB gives the i ,/ -diol 47 with 82% ee in 88% yield [55]. 

Whereas the chiral TEMPO analog 87 was used to resolve racemic secondary alcohols, the D-fructose-derived ketone 88 [137] proved useful for oxidative resolution of racemic diols (Table 10.13) [138, 139], Persulfate in the form of Oxone, Curox, etc., served as the final oxidizing agent, and the dioxirane generated from the ketone 88 is the chiral active species. Because of the relatively low conversions (except for unsubstituted dihydrobenzoin) at which the ee stated were achieved, the method currently seems to be of less practical value. Furthermore, typically 3 equiv. ketone 88 had to be employed [138, 139]. 

A series of meso-dihydrobenzoins was also subjected to oxidative desymmetrization. Three equivalents of the chiral ketone 88 again provided the chiral dioxirane as the active species [138, 139]. As shown in Table 10.14, enantiomeric excesses up to 60% were achieved. In addition to the meso diols themselves, acetonides also proved suitable substrates in two instances (Table 10.14). 

Adam et al. subjected a series of meso-dihydrobenzoins to oxidative desymmetrization, using three equivalents of the chiral Shi ketone 54 as catalyst. In the presence of peroxomonosulfate (Oxone, Curox etc.), the latter generates a chiral dkmrane as... 

Stereoselective cyclopropanation of cyclic enones dihydrobenzoin-derived chiral auxiliary... 

The synthesis of a typical compound containing two units of dihydrobenzoin is shown as an example in Scheme 7 [26]. Reaction of 2,6-bis(bromomethyl)l,4-dimethoxybenzene 41 with the dibutyltin derivative of optically active dihydrobenzoin 59 yields a chiral podand 60 in 63%. Cyclization of 60 with the ditosylates of oligoethylene glycols, followed by oxidation with CAN and treatment with dinitrophenylhydrazine, affords the desired chiral dyed acerand 53. Some chiral azophenol acerands 51-58 are synthesized in a similar manner. 

Under mechanochemical conditions, bifunctional benzil 71 is specifically reduced by NaBU, when used in a 4 1 stoichiometric ratio to quantitatively give racemic benzoin 72 (Scheme 6.26). Such result has never been described in solution reactions of these reagents. Furthermore, both carbonyl groups of 71 were quantitatively reduced to dihydrobenzoin (17/18), if a 2 1 ratio of 71 and NaBU, was applied under the otherwise identical conditions of Table 6.17. This stoichiometric synthesis provides meso-13 and rac-74 in 80% and 20% yields, respectively. This stereoselectivity compares with the reported 100 0 ratio in methanol (2h at 25°C) and the 85 15 ratio of 73/74 in ethanol (overnight). 

The Separation of the Enantiomers of Dihydrobenzoin at Different Resolution Monitored by the PDR Chiral Detector and the UV Detector Courtesy of PDP-Chiral Inc. 

Enantiomer selective coloration of optically active amines, our important project, was realized by chiral azophenol crown 4 incorporated with two units of optically active hydrobenzoin. The synthetic route is shown in Scheme 2. Reaction of 2,6-bis(bromomethyl)-l,4-dimethoxybenzene 22, which is derived from hy-droquinone monomethylether 19 by a three-step procedure, with the dibutyltin derivative 26 of optically active dihydrobenzoin gives optically active podand 23 in 63% yield. Cyclization of 23 with the ditosylate of polyethylene glycol, followed by oxidation with ceric ammonium nitrate (CAN) and treatment with dinitrophenylhy-drazine, affords the desired chiral azophenol crowns 4n. 

A similar reaction sequence accounts for the formation of 1,l-dichloro-2,2,3,3-tetramethylcyclopropane in 15% yield from the reaction of pinacol with dichloro-carbene. Likewise, reaction of m 5o-dihydrobenzoin with dichlorocarbene gave a 15% yield of cw-stilbene [10] (Eq. 3.7). 

Benzoin methyl ethers have been incorporated into a polycarbonate chain. The synthesis was achieved by polycondensing bisphenol A with phosgene in the presence of 4,4 -dihydrobenzoin methylether [216]. Irradiation of the resulting poly condensate in the presence of methyl methacrylate... 

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