Hydrogenation diphenylmethanol

Scheme 6.5 Reaction scheme for benzophenone hydrogenation. DPM diphenylmethanol CHPK cyclohexyl phenyl ketone CHPM cyclohexylphenylmethanol DCHK dicyclohexyl ketone and DCHM dicyclohexylmethanol. (Reproduced from Reference [34].)...

Therefore we used 4-androsten-3,17-dione 1 and 5a-androstan-3,17-dione 2 as model substrates to investigate the chemo- regio- and stereoselectivity of hydrogen transfer from different secondary alcohols, 2-propanol, 2-octanol, cyclohexanol, 1-phenyl-ethanol and diphenylmethanol in the presence of CU/AI2O3. In particular, hydrogenation of 1 allowed to determine the selectivity towards 5p isomers, whereas the percent of axial alcohol was derived from the hydrogenation of 2. These results can be compared with those obtained with the same catalyst in the presence of molecular hydrogen. 

Further applications of the silane/acid (i. e. 720/trifluoroacetic acid) system include reductions of steroidal substrates95,96 Another notable variant is the use of methylpolysiloxane (757)88 97 especially in presence of bis(dibutylacetoxytin)-oxide (DIBATO)97 as hydrogenating agent via this method benzophenone (135) yields diphenylmethanol (138) (Scheme 16). Under hydrosilylation-like conditions... 

However, under somewhat different conditions (aqueous acetonitrile at 85°), no evidence for the free carbonium ion could be found (Bethell et al., 1965). Moreover, the invariance of the product proportions when water is replaced by deuterium oxide, coupled with the observation of a large tritium isotope effect on the formation of diphenylmethanol, is consistent only with the ylid mechanism (equation 21) (Bethell et al., 1969). For reaction of diarylmethylenes with alcohols, substantial hydrogen-isotope effects are observed, consistent with both equations 21 and 22. 

An example concerns the hydrogen bond dynamics in selectively deuterated ferrocene-1,l -diylbis(diphenylmethanol-d1). In this structure, the molecules form hydrogen bonded dimers, with the oxygen atoms of four hydroxyl groups involved in a folded trapezium hydrogen bonding arrangement [33] shown schematically in Fig. 2 as a square. 

The behavior of arylmethanols towards anhydrous hydrogen fluoride is very specific. In cases where dehydration is possible yields are usually low or the fluorinated products are unstable. Diphenylmethanol, which cannot lose water, gives only bis(diphenylmethyl) ether (78 % yield) upon treatment with anhydrous hydrogen fluoride at low temperature. However, good to excellent yields of fluorides 3 are obtained from highly halogenaled arylmethanols and (nitro-aryl)methanols. 

Among alcohols, 2-propanol and diphenylmethanol stand out with respect to their reactivity in hydrogen transfer reactions with azoalkanes [45,48]. The abstraction from secondary a-CH groups with two radical-stabilizing substituents, i.e methyl or phenyl, proceeds with quite high rate constants, due to strongly exergonic thermodynamics [184]. 

Although the CSDP acid method was easily applicable to o-methoxy-substituted alcohol 22 (entry 11), o-methyl-substituted alcohol 23 could not be enantioresolved as the CSDP acid esters because of the small difference between o-methyl and hydrogen groups. So, the indirect method was adopted as follows. o-Hydroxymethyl-diphenylmethanol 24 was enantioresolved as CSDP esters, where the primary alcohol moiety was esterified, and the AC of the second-eluted ester was determined by X-ray crystallography (entry 12). Enantiopure alcohol (7 )-(+)-24 was then converted into the target compound (R)-(—)-23. It should be noted that the AC of alcohol 23 was originally proposed on the basis of an asymmetric reaction mechanism, but it was revised later by this study. The data of alcohols 25 and 26 indicate that the HPLC separation as CSDP esters is easier for silyl ethers (entries 13 and 14). ... 

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