Phosphorus, alkylation reactions under oxidizing conditions

It has already been indicated that the course of any reaction may depend, to some extent, on the nature of the phosphite (or phosphonite) ester (phosphinite esters yield phosphine oxides). Thus, tris(perfluoroalkyl) phosphites do not undergo a Michaelis-Arbuzov reaction with perfluoroiodoalkanes, although reports on the outcome of any reaction between triethyl phosphite and CF3I, under normal conditions, are conflicting reactions do appear to proceed under photostimulation. A normal reaction does take place at high temperatures between polyfluorinated trialkyl phosphites and methyl iodide, when the product, MeP(0)(0Rf)2, is accompanied by oxidation of the phosphite to phosphate Either elimination or alkylation accompanies the formation of unidentified phosphorus-containing products in the reactions between trialkyl phosphites and the halides Cl3C(CF2) Cl n - 2, 4 or 6) ... 

Iron complexes containing bidentate alkyl and aryl phosphorus ligands cleave a variety of C-H bonds under mild conditions, Hydrido acetylide complexes were prepared by oxidative addition of primary acetylenes in the Fe(DPPE)2 and the Fe(DMPE)2 systems [DPPE = bis(diphenylphos-phino)ethane, DMPE = bis(dimethylphosphino)ethane]. The Fe(DMPE)2 system also cleaves C-H bonds of activated methyl groups, aromatic compounds, and certain other sp hybridized molecules. The C-H cleavage reactions are reversible, resulting in equilibrium mixtures of isomeric products in many cases. Studies of substituted benzenes show that while product stability is favored by electron withdrawing substituents, steric effects play a predominant role in the determination of product distribution. 

The dipolar character of phosphorus ylides is shown by their reactions with nucleophiles (e.g. aldehydes and ketones) or with electrophiles (e.g. proton donors). Ylides Ph3P=CHR (R = alkyl) are readily hydrolysed, even by cold water, so it is usual to carry out reactions involving them under anhydrous conditions. An inert atmosphere (usually nitrogen) is also necessary as oxidation... 

Organozincs generated under similar conditions have been shown to add to optically active vinyl phosphine oxides with retention of configuration at phosphorus [63] (Scheme 8). In this case a 1 1 zinc/copper couple was employed to activate the zinc. The one-pot reaction proceeded best with tertiary or secondary alkyl halides. The resulting phosphine oxides are used as chiral ligands for catalysts in asymmetric synthesis and were previously only available by reaction with the analogous cuprate [147] since conjugate addition of simple alkyl halides normally results in polymerisation. 

Thiane oxides have been shown to be reduced cleanly back to the thiane with phosphorus pentasulfide under conditions to which sulfones, sulfinates, ketones, esters and amides are inert (78CJC1423) the potential of this reaction, though not yet applied, is obviously considerable, especially when coupled with the old-established Raney nickel desulfurization technique. Thiane itself is desulfurized to pentane (with traces of cyclopentane) but the opportunity to construct alkyl chains of great complexity regio- and stereo-specifically is there. At the very least, the reduction to tetrahydrothiopyrans presents a very useful entree into a wide range of 2-substituted thianes (Scheme 2). 

The Michaelis-Arbuzov reaction is the most used and well-known method for the synthesis of phosphonates and their derivatives and may also be used to synthesize phosphinates and tertiary phosphine oxides. The simplest form of the Michaelis-Arbuzov reaction is the reaction of a trialkyl phosphite, 3, with an alkyl halide, 4, to yield a dialkyl alkylphosphonate, 6, and new alkyl halide, 7 (Scheme 2). During this transformation the phosphorus atom of a ter-valent phosphorus(III) species (3) acts as a nucleophile resulting in the formation of an intermediate alkoxy phosphonium salt 5, containing a new [P—C] bond. The precise structure of the intermediates 5 is a subject of debate—as reflected by common reference to them as pseudophosphonium salts —with a penta-coordinate species (containing a [P—X] bond) being proposed and detected in some cases.18 Decomposition (usually rapid under the reaction conditions) of the intermediate 5 by nucleophilic attack of X- on one of the alkyl groups R1, with concomitant formation of a [1 =0] bond yields the product pentavalent phosphorus(V) compound (6) and the new alkyl halide, 7. 

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