2.2- Diphenylethanal, by oxidation

Diphenylethanal, by oxidation of 1,1-diphenylethylene with chromyl chloride, 51,... 

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

Intermediates generated at an electrode surface may react while still near the electrode. If so, one side of the intermediate may be wholly or partly shielded from attack by other reactants by the electrode itself. Such behavior is particularly common in the electrochemical oxidation of aromatic compounds since, as we have already seen with coumarin, aromatic compounds are generally tightly adsorbed parallel to the electrode surface at potentials positive of the p.z.c. For example, electrochemical oxidation of the stilbenes in alkaline methanol affords a mixture of dl and meso-1,2 dimethoxy-1,2-diphenylethane (1) 10>. It is found that c/s-stilbene affords a mixture of isomers of 1 in which the... 

Alkoxycarbenium ion pools can also be generated by oxidative C-C bond dissociation. Oxidative C-C bond dissociation is well known in the literature.38 Thus, the electrochemical oxidation of l,2-dimethoxy-l,2-diphenylethane 32... 

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. 

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>. 

Rosini adapted the reaction conditions developed by Uemura and reported on a system using 10 mol % of (S,S)-l,2-diphenylethane-l,2-diol (12) as chiralHgand and tert-butyl hydroperoxide as the terminal oxidant. After optimization of the process, phenyl methyl sulfoxide was obtained in 60% yield with an ee of 80% [24]. 

It is noteworthy that the addition of a radical scavenger such as 2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) completely suppressed the reactivity, showing that a radical mechanism is most likely involved in the transformation. Furthermore, a significant amount of 1,2-diphenylethane was obtained under such standard conditions, which also supports the formation of a benzyl radical 6-D during the reaction (Scheme 4.6). Firstly, ferf-butyl peroxide decomposes to give a tert-butyl peroxide radical and oxidizes Fe(ii) 6-A into Fe(iii) 6-B, which reacts with the 1,3-dicarbonyl derivative leading to an Fe(iii) enolate 6-C. Meanwhile, a benzyl radical 6-D obtained by abstraction of H can then react with 6-C. 

In 2003, Sigman et al. reported the use of a chiral carbene ligand in conjunction with the chiral base (-)-sparteine in the palladium(II) catalyzed oxidative kinetic resolution of secondary alcohols [26]. The dimeric palladium complexes 51a-b used in this reaction were obtained in two steps from N,N -diaryl chiral imidazolinium salts derived from (S, S) or (R,R) diphenylethane diamine (Scheme 28). The carbenes were generated by deprotonation of the salts with t-BuOK in THF and reacted in situ with dimeric palladium al-lyl chloride. The intermediate NHC - Pd(allyl)Cl complexes 52 are air-stable and were isolated in 92-95% yield after silica gel chromatography. Two diaster corners in a ratio of approximately 2 1 are present in solution (CDCI3). 

Oxidations. Sulfides including P-keto sulfides give optically active sulfoxides by the Sharpless system with modification in using furylhydroperoxides. Alternatively, the tartrate ester may be replaced by (R.R)- or (S,51-diphenylethane-l,2-diol. ... 

A chiral Ti complex formed in situ by reacting Ti(0 Pr)4, (J ,P)-diphenylethane-1,2-diol, and water was reported to be effective for asymmetric oxidation of aryl alkyl and aryl benzyl sulfides using TBHP as the oxidant to obtain optically active sulfoxides in good yields and high enantiomeric excesses [274] (Scheme 14.115). 

A new catalytic procedure for the asymmetric oxidation of aryl alkyl and aryl benzyl sulfides to optically active sulfoxides by TBHP is mediated by a chiral titanium complex formed in situ by reacting Ti( -PrO)4, (R, / )-diphenylethane-l,2-diol, and water. The results were largely unaffected by the nature of the phenyl substituents, suggesting that the same mechanism operates in all cases. Only the / -N02 substituent on the aryl ring caused a considerable loss of enantioselectivity and this is attributed to the electron-withdrawing power of this group or, more likely, its coordinating ability. ... 

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