Trimethylsilyl- and trimethylstannyldimethylphosphane--convenient and versatile reagents for the synthesis of polyfluoroaryldimethylphosphanes.
Trimethylsilyldimethylphosphane (Me3SiPMe2) and the corresponding tin compound (Me3SnPMe2) were used as reagents for the substitution of fluorine by the Me2P group in polyfluoroarenes C6F5X (X = F, H, Cl, CF3) and C5NF5. The reactions occur even under mild conditions (T = 0-20 C), either in benzene or without solvent, to give as a rule 4-X-1-(dimethylphosphano)tetrafluorobenzenes (XC6F4PMe2, 1-4) and 4-(dimethylphosphano)tetrafluoropyridine (C5NF4PMe2, 5), respectively, in yields between 75 and 95%. In the case of C6F6, double substitution is also observed, which affords 1,4-bis(dimethylphosphano)tetrafluorobenzene (6). A very efficient route to the compounds XC6F4PMe2 (X = F, H, Cl, CF3) and C5NF4PMe2 was developed as a one-pot reaction of the corresponding fluoroarenes with tetramethyldiphosphane (P2Me4) and trimethyltin hydride (Me3SnH) at moderate temperatures. This process was tested for C6F6 and perfluorobiphenyl which gave C6F5PMe2 (1) and 4,4'-bis(dimethylphosphano)octafluorobiphenyl (7), respectively. The results, which included kinetic measurements that used the intensities of the 31P signals, revealed the influence of the substrate type on the rate of reaction in the sequence: C5NF5>C6F5CF3> C6F5Cl, C6F5PMe2>C6F5H>C6F6>> C6H5F. Ab initio calculations were carried out on the model reactions of pentafluoropyridine with silylphosphane, phosphane or phosphide to discriminate between possible reaction mechanisms. The novel phosphanes were characterised by spectroscopic investigations (NMR, MS), by preparation of the related thiophosphanes ArFP(=S)Me2 (8-14), their spectroscopic and analytic data and single crystal X-ray diffraction studies on five of these derivatives.
The preparation and properties of polyfluoro aromatic and heteroaromatic compounds
Abstract This review is concerned with ring systems formally recognised as “aromatic” and possessing a large proportion of fluorine atoms directly attached to the carbon skeleton. These include derivatives of the following: benzene and polynuclear benzenoid systems; pyridine, diaza- and triazabenzenes and some of their fused six-membered ring compounds; and a wide variety of fused ring carbocycles and heterocycles. Some highly fluorinated non-benzenoid aromatic compounds obeying the Huckel 4n + 2 π electron rule, as well as antiaromatic 4n π electron systems, are included in the survey. The wide variety of methods used for synthesising these highly fluorinated compounds, which enabled them to be regarded no longer as mere chemical curiosities, is presented. The chemical behaviour of polyfluoro aromatic and heteroaromatic compounds, at the fluorinated ring, forms the major proportion of this review: reactions with nucleophiles and a rationalisation of orientation reactions; reactions with electrophiles, free radicals, carbenes and nitrenes; the formation of stable salts of radical cations; photochemical reactions and the formation of valence isomers; and rearrangement reactions. Organometallic derivatives of polyfluorinated compounds have been extensively used in organic synthesis.
Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols.
Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.