Diphenylmethanols fluorinated

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. 

Various fluorinated diphenylmethanols 36-39 were also enantioresolved as CSDP esters (entries 23-26). In the case of alcohols 36, 37, and 39, their absolute configurations were determined by X-ray crystallography. To those fluorinated alcohols, the method of MaNP acid 3 could be applied for enantioresolution and also for determination of their absolute configurations by the H NMR anisotropy method, as discussed below. Meto-substituted diphenylmethanols 40 and 41 were enantioresolved by the CSDP acid method yielding enantiopure alcohols, the abso-... 

The MaNP acid method was also applied to racemic fluorinated diphenylmethanols 36, 38, and 39 (Table 9.3). A diastereomeric mixture of esters 73a and 73b prepared from (4-trifluoromethylphenyl)phenylmethanol 36 was separated well by HPLC on silica gel a = 1.39 Ps = 4.84 (entry 11). Other fluorinated diphenylmethanols were similarly esterified with (S)-(-i-)-3, and the diastereomeric mixtures obtained were subjected to HPLC on silica gel. Diastereomeric MaNP esters of (4-fluorophenyl)phenylmethanol 38 were separated well with a-values of 1.18 (entry 12). On the other hand, it was a little difficult to separate the diastereomeric MaNP esters of (2,6-difluorophenyl)phenylmethanol 39, because of its small a-va-lue a = 1.08. 

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