Phosphorus derivatives, alkylations, potassium

Alkylation of Phosphorus Derivatives. The formation of diethyl phosphite anions has been achieved successfully with KHMDS and LiHMDS. The following reaction with acid chlorides is strongly influenced by the counter-ion, as only the rearrangement product was observed with the lithium base, whereas the desired hydroxybisphosphate was the major product when using the potassium base (eq 48). 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Pd-catalyzed asymmetric allylic alkylation is a typical catalytic carbon-carbon bond forming reaction [ 126 -128]. The Pd-complex of the ligand (R)-3b bearing methyl, 2-biphenyl and cyclohexyl groups as the three substituents attached to the P-chirogenic phosphorus atom was found to be in situ an efficient catalyst in the asymmetric allylic alkylation of l-acetoxy-l,3-diphenylprop-2-en (4) with malonate derivatives in the presence of AT,0-bis(trimethylsilyl)acetamide (BSA) and potassium acetate, affording enantioselectivity up to 96% and quantitative... 

The cleavage of tetrahydrofuran and its alkylated derivatives with halogen acids is an excellent method for the preparation of, A-dihalo-alkanes.The reaction of tetrahydrofuran with the less-reactive hydrogen chloride stops at the chlorohydrin stage, whereas the reaction in the presence of zinc chloride catalyst leads to the formation of the dichloride. The crude reaction mixture containing the intermediate chlorohydrin may be treated directly with phosphorus tribromide, yielding tetramethylene chlorobromide. The preparation of dibromides can be accomplished easily with hydrogen bromide or phosphorus and bromine and diiodides, by the action of potassium iodide and orthophosphoric acid. ... 

Alkyl and Aryl Derivatives.—Potassium amide has been shown to cleave benzyl groups from phosphorus in liquid ammonia at 120 °C ... 

The chemistry of l-phospha-4-boracyclohexa-2,5-dienes has been further developed to include preparations of the less substituted derivative (44) and its 1-arsa analogue (45) which is formed as a 2 1 mixture with its dihydro counterpart (46) (Scheme 6). The chemistry of (5) includes its methanolysis to (47), its oxidation with chalcogens to phosphorus(V) compounds (48), and its conversion to F-methyl and ethyl derivatives (49) with potassium in DME followed by alkylation with alkyl halides. The. B-r-butyl derivative (50) is also available from the addition of the alkylithium, but attempts to prepare the corresponding 5-Me derivative were thwarted by the failure of the intermediate ate complex (51) to undergo demethoxylation <83JOM(250)33>. 

A variation of the Wittig reaction that can overcome problems with the stereochemical outcome is the Homer-Wittig reaction with phosphine oxides. The oxides are obtained by quatemization of triphenylphosphine and hydrolysis of the phosphonium salt, or by reaction of hthiodiphenylphosphide with an alkyl halide or sulfonate and oxidation of the resulting phosphine with hydrogen peroxide. The derived hthio species react with aldehydes or ketones to give p-hydroxy phosphine oxides, which ehminate on treatment with a base such as sodium hydride or potassium hydroxide to form the alkene. In common with the Homer-Wadsworth-Emmons reaction, the phosphorus by-product is water soluble and easily removed from the product. 

Some alternative but related methods for the homologation of glycine have also been developed. Bis(diphenylphosphino)glycine methyl ester yields an enolate (189), when treated with potassium t-butoxide, which can be cleanly monoalkyl-ated with, for example, benzyl bromide. The phosphorus group is removed by acid hydrolysis. The oxazolin-5-ones (190), derived from A/ benzoyl-a-amino-acids and acetic anhydride, can be readily alkylated in the 4-position hydrolysis gives a,a-disubstituted JV-benzoyl-a-amino-acids. ... 

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