A-fluoro compounds

This section focuses on the preparation of fluorinated compounds through asymmetric hydrogenation/reduction reactions and nucleophilic additions by listing some examples. The first successful example of catalytic asymmetric hydrogenation of a fluoro-compound was reported by Konig et al.81... 

Preliminary fluorination experiments using optically active A -fluoro compounds ( —)-2b and ( + )-2c show that there is reaction with various metal enolates (Table 16) generated under standard reaction conditions to give the anticipated a-fluoro carbonyl compounds with enantiomeric excesses depending strongly on the structure of the metal enolate.119... 

See Acetonitrile A-Fluoro compounds See other DIFLUOROAMINO COMPOUNDS... 

The anions of malonaldehyde [106, 107] and of organophosphonates [108, 109, 110] are fluorinated in good yields to provide interesting fluorinated intermediates The A -fluoro compound B in Table 3a is also effective m the fluorination of phosphonate anions [109] (equations 60 and 61). 

Samples of the A-fluoro compound, either alone or in admixture with the difluoride, exploded forcefully while wanning from —196°C to -l-22°C. Sample size should not exceed 3 mmol. 

The phenylsulfoxides are also superior to the phenylsulfides when the corresponding ot-hydroxy or a-fluoro compounds are reduced322 323. The superiority of the phenylsulfoxides to the phenyl-sulfenyl and phenylsulfinyl groups may result from its greater electron-withdrawing effect. The introduction of a hydroxyl group at the end of the alkyl chain improves the reduction322. 

Little importance attaches as yet to A-fluoro compounds. Attempts to prepare them have usually given mixtures or perfluoro compounds.194,423... 

R Li, R MgBr, R 2CuLi or R 2CuMgBr, in THF at -78 °C. In the case of the a-fluoro compound, the final alkylation step evidently works well only with Me2CuLi. 

Several methods are available for the preparation of perfluorinated cyclic imidoyl fluorides. For example, reductive defluorination of cyclic A-fluoro compounds... 

Direct fluorination (F2-N2) of the potassium salts of a number of aryldinitro-methanes [ArCHCN02)2 in most examples Ar = nitro- or polynitro-phenyl] in aqueous solution gives good yields of a-fluoro-compounds [ArCF(NOa)2], and the iW-difluoroanilines 2,4,6,3-(02N)3RC6H NF2 (R = H or Me), which may be useful as components of propellants, are obtained from the parent anilines and fluorine in anhydrous HF at — 5 to 0 Russian work on the reactions of aromatic carboxylic acids with sulphur tetra-... 

The 1980s saw the emergence of a suite of A-fluoro compounds, which have since become the reagents of choice for electrophilic fluorination of organic compounds, that is, as F+ donors. Some popular A-fluoro reagents are depicted in Figure 7.1... 

Actually, the tynthesis of 3 -fluoro-tylosyladenine and 3 -fluoroadenosines (3a and 4a, respectively) have recently been reported by Herdewijn et aL These authors used 9-6-D-xylofuranosyladenine as the starting material, which was tritylated in 50% yield to the corresponding 2, 5 -di-0-triyl-N -trityl derivative and then treated with DAST. This reaction yielded the expected 3 -a-fluoro compound in 78% yield. Detritylation, however, was rather disappointing (46%). ... 

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