1.2- Ethanediol, 1,2-diphenyl

Exercise 16-44 Strong acid converts 1,1 -diphenyl-1,2-ethanediol first to diphenyl-ethanal and then more slowly to 1,2-diphenylethanone (benzyl phenyl ketone). Explain how and why kinetic and equilibrium control may be expected in this case to give different products. 

What are the products from the reaction of 1,1-diphenyl-1,2-ethanediol with strong acid Propose a reasonable mechanism for the reaction. 

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. 

Easily accessible acetals and ketals of a,p-unsaturated aldehydes and ketones derived fi-om C2-symmetric chiral 1,2-diols have been successfully used with Simmons-Smith reagents furnishing cyclopropane aldehydes with high selectivity and recovery of the auxiliary. Thus, dialkyl tartrates proved to be superior compared to 1,2-diphenyl-ethanediols as chiral auxiliaries in reactions of a,p-unsaturated aldehydes. 

Fig. 57. The subsequent elimination of water from the 4 -aminomethyl-2,2-diphenyl-ethanediol handle, which activates the peptide anchoring ester bond in the polymer phase...

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. 

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. 

The first method is successful on a large scale with methadone (3) and l,2-diphenyl-l,2-ethanediol (hydrobenzoin, 4). 

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. 

Diaryl ketones do not undergo photodissociation in the same way as alkyl ketones, probably because cleavage to phenyl and other aryl radicals is unfavorable (Table 4-6). Nevertheless, aromatic ketones are photochemically reactive in the presence of compounds that can donate a hydrogen atom, with the result that the carbonyl group is reduced. Indeed, one of the classic photochemical reactions of organic chemistry is the formation of 1,1,2,2-tetraphenyl-1,2-ethanediol (3, benzopinacol) by the action of light on a solution of diphenyl-methanone (2, benzophenone) in isopropyl alcohol. The yield is quantitative. 

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]. 

Details for the large-scale synthesis of (R,R) 1,2-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, Column 9) however, the Organic Synthesis procedure [47] is still an excellent choice for preparing large amounts of the... 

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. 

ETHANEDIOL DIPROPANOATE (9CI) see COB260 ETHANEDIONE, DIPHENYL-, MONOOXIME see BCA300... 

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>. 

In cyclic acetals, IX may be substituted at C2, C4, and C5. A tram arrangement of substituents at C4 and C5 will be more stable than a cis arrangement, as is clearly shown by the quantitative measurements on the cyclic 0-isopropylidene derivatives of erylhro- and threo-1,2-diphenyl-1,2-ethanediol, and the qualitative evidence given in Section V. The order of stability for isomeric derivatives with substituents at C2 and C4 (or C5) cannot be predicted by the method used for the 1,3-dimethyl-cyclopentanes, since that takes into account the puckering of the cyclopentane ring. 

Example 4.11. The rearrangement of l,2-diphenyUl,2-ethanediol to 2,2-diphenyl-ethanol. 

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