Phosphorus halides reaction with

The mechanism for the reactions with phosphorus halides can be illustrated using phosphorus tribromide. Initial reaction between the alcohol and phosphorus tribromide leads to a trialkyl phosphite ester by successive displacements of bromide. The reaction stops at this stage if it is run in the presence of an amine which neutralizes the hydrogen bromide that is formed.9 If the hydrogen bromide is not neutralized the phosphite ester is protonated and each alkyl group is successively converted to the halide by nucleophilic substitution by bromide ion. The driving force for cleavage of the C—O bond is the... 

Replacement of the hydroxyl group in a phenol by halogen cannot be accomplished by reaction with the hydrogen halides as in the case of alcohols, and reaction with phosphorus halides gives only low yields of halogenobenzenes (except in the case of nitrophenols), the main product being a phosphite or phosphate ester. 

Reaction with Phosphorus Halides or Thionyl Chloride. 253... 

The carbonyl tautomers deprotonate at N-H, generating ambident anions that can react at either oxygen or nitrogen, depending on the exact conditions for example 0-alkylation can be achieved with silver carbonate. They are converted, as with the pyridones, into halo-quinolines and halo-isoquinolines by reaction with phosphorus halides. 

A number of 2,4-i 890, 574, 796, 820, 835, 840 and 2,6-dihydroxypyri-dines 866, 84i have been converted into dichloropyridines by reaction with phosphorus halides. Frequently, but not invariably, these reactions have... 

Reaction with phosphorus trihalides (Section 4 13) Phosphorus trichloride and phosphorus tribromide convert alcohols to alkyl halides... 

In a similar vein, the keto bridge in 5 can be replaced by oxygen with retention of activity. Reduction of acetophenone derivative 19 by means of sodium borohydride leads to the corresponding alcohol (20). Reaction with phosphorus tribromide with cyanide gives... 

Arbusov reaction of thienyl halides with phosphites in the presence of nickel catalyst [41, 42], or palladium catalyzed phosphorylation of thienyl halides [43], and some of them are commercially available (Scheme 22). 2,5-Diphosphorylthiophenes were synthesized by Arbusov reaction of thienyl halides with phosphites in the presence of nickel catalyst [44] or reaction of 2,5-dilithiothiophene with phosphorus halides followed by oxidation [45] (Scheme 23). 

These reactions may be considered to be a method of obtaining 1,3,2,5-dioxaborataphosphoniarinanes with different substituents at carbon and phosphorus atoms of the ring. Comparing the properties of cyclic oxyalkyl-phosphines and boryloxyalkylphosphines, it should be noted that in both cases the reaction with alkyl halides results in the formation of a tertiary phosphonium salt. The reaction with electrophilic reagents such as diphe-nylchlorophosphine and diphenylchloroborane proceeded quite differently [Eq. (100)]. 

Simple reaction occurs with aryl halides only when the ring is sufficiently substituted with electron-withdrawing functions to allow attack by the nucleophilic phosphorus.53-56 Generally, reaction with aryl halides requires the presence of a Lewis acid catalyst or some other means of reaction initiation. These reactions will be considered in detail in Chapter 6 of this work. Interestingly, while reactions involving vinylic halides seem to correlate with those of aromatic halides (see Chapter 6), acetylenic halides undergo facile reaction with these phosphorus reagents.57 58... 

Several methods for the preparation of the parent compound in this system, tris(trimethylsilyl)phosphite, have been reported.114 118 The application of this and related reagents in reaction with alkyl halides has been reported and used for the preparation of a variety of phosphonic acid analogues of phospholipids.114119-124 Interestingly, alkyl chlorides appear to be more reactive with the silyl reagents than do alkyl iodides, a reversal of the normally observed trend with alkyl esters of the phosphorus acids. (The particular use of silyl phosphorus reagents for the synthesis of biologically significant compounds has... 

A commonly used and important reaction of sulfonic acids, or sulfonates, is their conversion to sulfonyl chlorides by treatment with phosphorus halides, or sometimes with thionyl chloride. Although it is easy to postulate mechanisms for this conversion, the exact path followed has never been determined. Similarly, although mechanisms can be suggested for other known reactions involving sulfonic acids, such as the cleavage of dialkyl ethers by anhydrous sulfonic acids (Klamann and Weyerstahl, 1965), or the formation of sulfones by treatment of an aromatic hydrocarbon with a mixture of sulfonic acid plus polyphosphoric acid (Graybill, 1967), nothing truly definitive is known about the details of the actual mechanisms of these reactions. 

Reaction of 2-methylpyridine iV-oxide with p-toluenesulfonyl chloride or phosphorus oxychloride gives 2-pyridylmethyl chloride (Scheme 47), and related reactions with reactive halides have also been studied (62JOC3856, 81JHC939). 

Chloro- and bromo-l,3,4-thiadiazoles are usually prepared by nucleophilic processes, e.g., Sandmeyer reactions of diazonium salts [56CB1534 68AHC(9)165 86CHE1148], and reactions of thiadiazolinones with phosphorus halides [68AHC(9)165]. The halogeno derivatives are important... 

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