Fluoroalcohols, chiral

Popova and colleagues47 carried out TLC of oxidation products of 4,4 -dinitrodiphenyl sulphide (the sulphoxide and sulphone) on silica gel + a fluorescent indicator, using hexane-acetone-benzene-methanol(60 36 10 l) as solvent mixture. Morris130 performed GLC and TLC of dimethyl sulphoxide. For the latter, he applied a 6% solution of the sample in methanol to silica gel and developed with methanol-ammonia solution(200 3), visualizing with 2% aqueous Co11 thiocyanate-methanol(2 1). HPLC separations of chiral mixtures of sulphoxides have been carried out. Thus Pirkle and coworkers131-132 reported separations of alkyl 2,4-dinitrophenyl sulphoxides and some others on a silica-gel (Porosil)-bonded chiral fluoroalcoholic stationary phase, with the structure ... 

Chiral solvating agent each agent was determined to be more than 90% enan-tiomerically pure, except for Id and le whose purity was found to be ca. 80% hence data obtained by these two fluoroalcohols has been corrected to 100%. Unless otherwise noted, the molar ratio of CSA to solute is between 2.4 and 3.3. From ref. 21. 

Oxazolidine 198 was produced from condensation of (R)-phenylg-lycinol and fluoral ethyl hemiacetal as a 62 38 tram/cis diastereomeric mixture. The enantiopure trans-198 was obtained through an epimeriza-tion with p-toluenesulfonic acid that realized the selective precipitation of the desired diastereoisomer. The repetition of this crystallization-induced dynamic resolution (CIDR) protocol on mother liquors allowed an almost complete conversion of the initial mixture into the desired trans-198. This chiral oxazolidine was used as chiral auxiliary for the synthesis of a-fluorocarboxylic acids and P-fluoroalcohols in a one-pot procedure that also allowed its recovery without loss of optical purity (13JOC3487). 

Scheme 7.7 Novel axially chiral phosphane ligand with a fluoroalcohol moiety and the proposed catalytic cycle in the arylation of aromatic aldehydes with boronic acids catalyzed by rhodium, as described by Amii and coworkers [13].

The case of a-fluorodnnamyl alcohol [48,39] is a clear example of how ene reductases are superior in terms of chemoselectivity with respect to metal-based hydrogenations, since in the latter, in addition to the C=C double bond reduction, the cleavage of C—F bond also takes place. Chiral fluoroalcohols are important synthones in medidnal chemistry. 

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