1.2- diphenyl-l,2-ethanediol

Other chiral diols, such as (1S,2S)-1,2-diphenyl-l,2-ethanediol and diethyl (1 /f,2/ )-l,2-di-hydroxybutanedioate offer only low atropdiastereoselectivity or, in the case of the 1,4-diol, (4.S, 55 )-4,5-bis(hydroxymcthyl)-2,2-dimethyl-1,3-dioxolane, no atropdiastereoselectivity at all28a. 

IR, 2R) -1,2-Diphenyl-l,2-ethanediol(3a) When the ether solution of racemic l,2-dipheny-l,2-ethanediol, which was prepared according to the known procedure was permitted to evaporate gradually in about two weeks, large crystals of R- and S- diols were formed separately and identified by measuring their optical rotations. This procedure easily gave near quantitative yields of R-diol as well as S-diol after re-cycling (R mp 148-149 °C, +94.8°(c 1.0 EtOH), NMR (003)200... 

Ligustrum also contains a unique volatile oil consisting primarily of esters and alcohols, with lesser amounts of thioketones, hydrocarbons, and traces of amines and aldehydes, but no terpene hydrocarbons. Major components of the volatile oil include ethyl acetate (18.95%), thioketone (8.56%), a-butyl-benze-nemethanol (5.6%), 4-acetyloxy-2-butanone (5.46%), 1-phenyl-1,2-butanediol (4.12%), 1,2-diphenyl-l,2-ethanediol (3.92%), hydra-zine-methyl-oxalate (3.52%), a,a,4-tri-methyl-3-cyclohexene-methanol (3.24%), 1-methyl-l-propyl-hydrazine (2.60%), and (Z)-1 -(1 -ethoxy-ethoxy)-3-hexene (1.89%). ... 

An early report that the threo and erythro isomers of 1,2-diphenyl-l,2-di(l-naphthyl)ethanediol gave two different products (a ketone and an unidentified substance) could not be substantiated by other workers, who also found that the threo and erythro isomers of l,2-bis(2-chlorophenyl)-l,2-diphenyl-ethanediol both gave the same ketone (phenyl migration). Yields were not recorded, precluding substantive mechanistic interpretation. 

From a practical point of view ketals derived from 1,2-diphenyl- 1,2-ethanediol (hydrobenzoin) are most useful because the diastereomeric ratios are very high and the auxiliary is available in both enantiomeric forms. In addition, most of the derived cyclopropanes are crystalline and their diastereomeric purities can easily be improved by recrystallization from diethyl ether62. Thus, (l/<,65 )-bicyclo[4.1.0]heptan-2-one is available with >99% ee by hydrolysis of recrystallized (l.R,4, S, 5, S, 6,S)[4, 5 ]diphcnylspiro[bicyclo[4.1.0]heptane-2,2 -[l, 3 ]dioxolane]62. The Sim-mons-Smilh reagents add to related ot,/3-unsaturated ketals derived from cyclopentenone, cycloheptenone and a bicyclic enone, also with similarly high diastereoselectivities62. 

Several results were reported by Russian authors. They are completely different from those reported above. Sorokin14 found an overall reaction order of 2 for the system heptanoic acid/l,2-ethanediol/diphenyl oxide. Bolotina16 studied the reaction of 2-ethylhexyl hydrogenphthalate with 2-ethylhexanol in the corresponding diester and found an order of 1 with respect to acid and of 2 with respect to alcohol. 

Diarytphenanthrenes. Tetraaryl-l,2-ethanediols are converted to phenan-threne derivatives on exposure to triflic acid. An exception is 1,2-diphenyl-1,2-di(3-pyridyl)ethanediol, which undergoes normal pinacol rearrangement. 

Recently, Koitai et al. (17) have shown that 5,5-diphenyl-2,4-thiazolidinedithione (15) with aluminum chloride in refluxing toluene gives 4,5-diphenyl-A-4-thia2oline-2-thione (16) (Scheme 7). 3-Methyl-4,5-diphenyl (17) and 4,5-diphenyl-A-4-thia2oline-2-thiones (16) are obtained in very low yields (1 to 5%) as by-products of the reaction between deoxybenzoin. benzoin. l,2-diphenyl-1.2-ethanediol. 1.2-diphenylethanol, or benzil, and Sg in hexamethylphosphoamide (18), The transformation of A-4-thiazoline-2-ones to the corresponding thiones by P2S5 (19) is of little synthetic value since the latter are more easily prepared. 

Periodic acid is a versatile oxidant since, depending on pH, the redox potential for the periodate-iodate couple varies from 0.7 V in aqueous basic media to 1.6 V in aqueous acidic media.Based on this observation, Villemin and Ricard devised an oxidative cleavage of glycols, in which mcjo-l,2-diphenyl-1,2-ethanediol was oxidized by periodic acid on alumina to benzaldehyde in 82% yield in aqueous ethanol (90% ethanol) at room temperature in 26 h. The same supported oxidant converted aromatics into quinones. In the presence of transition metal complexes (Mn ), a-arylalkenes suffer oxidative cleavage to aldehydes. For example, tran.r-stilbene gives benzaldehyde at room temperature. 

A detailed preparation of (/ ,f )-l,2-diphenyl-l,2-ethanediol using the 1 b/NMO system has also been reported 16. This method, although older than the above mentioned one, is still convenient for the large-scale and fast preparation of crystalline stilbene diols using small amounts of solvent. 

Reaction of cyclic sulfates or thionocarbonates, derived from 1,2-diols, with telluride results in stereospecific alkene formation <1995TL7209>. This is illustrated by the conversion of the cyclic sulfate OTitra-l,2-diphenyl-l,2-ethanediol 49 into fif-stilbene exclusively by Te, as shown in Equation (13). Treatment of the cyclic sulfate of 47-1,2-diphenyl-1,2-ethanediol with Te produces /ra r-stilbene exclusively. These results are accounted for by intermolecular Te Sn2 displacement followed by intramolecular Sn2 displacement to form the corresponding tellurirane. The tellurirane then thermally loses tellurium stereoselectively forming alkene. Cyclic sulfates need not be used dimethanesulfonates or di-/i-toluenesulfonates prepared from 1,2-diols also, stereospecifically, provide alkenes via telluriranes <1993CC923, 1996SL655>. 

Many dioxolanes. particularly those where the diisopropylidene unit is used as a protecting group for diols, have already been discussed in Sections 4.2. and 4.3. (derivatives of tartaric acid and carbohydrates). In addition, vinylketene acetals containing the 1,2-dioxolane moiety, e.g., 1, have been prepared from chiral diols, such as l,2-diphenyl-l,2-ethanediol (see Section 4.1. for access to the starting material) by the pathway outlined. This involves selective conversion of the (/ ,/ )-diol to (1 / ,2S )-2-chloro-l, 2-diphenylethanol (with inversion of the configuration)1, followed by esterification with 3-meihyl-2-propenoic acid and base-induced rearrangement2. Such dioxolanes have been used for diastereoselective Diels-Alder reactions (Section D. 1.6.1.1.1.1.4.4.). 

Alkylation Reactions. DMF dialkyl acetals undergo a variety of reactions with 1,2-diols. For example, the reaction of trans-cyclohexane-l,2-diol with DMF dimethyl acetal leads to the formation of cyclohexane epoxide (eq 2) with inversion of configuration. Similarly, wej 0-l,2-diphenyl-l,2-ethanediol gives trans-stilbene epoxide stereospecifically (eq 3). This method has also been applied in the synthesis of cholestane epoxide from vicinal diols. If the intermediate 2-dimethylamino-1,3-dioxolane is treated with Acetic Anhydride, reductive elimination to the alkene occurs with retention of stereochemistry (eq 4). " ... 

Details for the large-scale synthesis of (/(,/l)-l,2-diphenyl-1,2-ethanediol by using the DHQD-CLB/NMO variation of catalytic AD have been published [47]. Under these conditions the crude diol is produced with 90% ee and upon crystallization, essentially enantiomerically pure diol is obtained in 75% yield. Subsequent improvements in the catalytic AD process now allow this dihydroxylation to be achieved with >99.8% ee (entry 20, Colunm 9) however, the Organic Synthesis procedure [47] is still an excellent choice for preparing large amounts of the... 

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