Triphenylphosphine dibromide, reaction with

Since hydrogen peroxide, like alkyl hydroperoxides, can be alkylated by alkyl bromide plus silver trifluoroacetate (Eq. 19, R = H),35) an attractive variation of the silver-salt-induced dioxabicyclization uses cis- 1,3-dibromocycloalkane 43 as starting material. Thus Porter and Gilmore obtained 2,3-dioxabicyclo[2.2.1]heptane 9 in 30-40% yield from c s-l,3-dibromocyclopentane, which was itself obtained from the corresponding c/s-diol by reaction with triphenylphosphine dibromide (Eq. 31 R = R = H)36). 

Several papers have been devoted to the subject of reactions of phosphoranes with carboxylic acids and their derivatives. Thus triphenylphosphine dibromide (111) in acetonitrile cleaves lactones,93 while the corresponding dichloride (112) converts esters into acid chlorides.94 The reactions of esters with phosphorus pentachloride (101) have been studied further,95 and the influence of structural changes on the yields of products (113) and (114) has resulted in minor modifications to the mechanism previously96 outlined. 

The starting diol was transformed into the dibromide by elemental bromine with triphenyl phosphine adduct which undergoes the Arbuzov-Michaelis reaction under somewhat drastic conditions at 150 °C (step a). Catalytic removal of the benzyl group was performed by a Pd/C catalyst (step b) and the alcohol formed was allowed to react with dichloropurine in the presence of triphenylphosphine and diethylazodicarboxylate (Mit-sunobu reaction) (step c). Finally the desired product was obtained by reaction with methylamine (step d) and the removal of ethyl groups at the phosphorus centre was performed by transilylation using trimethyliodosilane (step e). 

There are many heterocyclic molecules in which 1,3,4-thiadiazoles are fused to other ring systems. For example, Molina et al. developed a procedure for building a thiadiazole ring on to a properly substituted imidazole moiety (Scheme 29). Reaction of l-amino-2-methylthio-4-phenylimidazole (161) with triphenylphosphine dibromide in dry benzene furnished the 2-methylthio-4-phenyl-l-triphenylphosphoranylidenamino imidazole (162) in a 95% yield. With aroyl chlorides at elevated temperature, this gave the 2-aryl-6-phenylimidazo[2,l-Z ][l,3,4]thiadiazoles (164) in yields between 50% and 70% via the imidoyl chloride intermediate (163) which could be isolated and shown to cyclize to the thiadiazole. The method developed for the imidazole ring was also applicable to the thiadiazolotriazine ring system <88H(27)1935). 

Bls(2,2,2-triflnoroethoxy)triphenylphosphorane, (C6H5)jP(OCH,CFj)2, (1). Mol. wt. 460.36, hygroscopic, stable in solution at 25 for several weeks. The phosphorane is prepared by reaction of triphenylphosphine dibromide with sodium 2,2,2-trifl uoroethoxide. 

This reaction can also be conducted with triphenylphosphine in the presence of carbon tetrachloride and triethylamine, or with triphenylphosphine dibromide in the presence of triethylamine. to give carbodiimides 40. 

Substitution reactions involving 3/S-hydroxy-A -steroids and their derivatives require special mention. Cholesterol reacts with a variety of halogenating agents, including thionyl chloride / StJ, phosphorus pentachioride [81], haHdes of aluminium or titanium [82], 2-chloro-i,i,2 trifluoroethyl di-ethylamine [83] and triphenylphosphine dibromide [55], to... 

Aziridines. The reaction of /3-amino alcohols (1) with triphenylphosphine dibromide in acetonitrile (triethylamine) gives aziridines (2) in about 50% yield.4 Piperazines (3) are formed as by-products. 

Isonitriles are obtained in 50-70% yield by the reaction of triphenylphosphine dibromide with monosubstituted formamides ... 

Formylation.1 A new variation of the Vilsmeier formylation reaction involves the reaction of triphenylphosphine dibromide with DMF in the presence of a suitably substituted substrate. The actual formylating reagent is considered to be (1). 

Acylsulfenyl halides are formed by the reaction of N-bromosuccinimide or tert-butyl hypochlorite with thiocarboxylic acid O-trimethylsilyl esters164 (equation 172). Treatment of silyl carboxylates with triphenylphosphine dibromide gives the corresponding acyl bromide along with the silyl bromide165 (equation 173). It is also possible to convert silyl ethers to the alkyl bromide with this reagent165 or with a mixture of carbon tetrabromide and triphenylphosphine166. The mild nature and selectivity of the reaction is underscored by the conversion of the trimethylsiloxy /Mactam 83 to the bromide 84165 (equation 174). 

Selenoketones. Barton et al. have converted ketones into the corresponding selenoketones by treatment of the hydrazone with triphenylphosphine dibromide to give the ketone triphenylphosphazine, for example (1). This derivative (1 eq.), when heated with selenium (2 eq.) and a trace of triethylamine at 120° for 20 hr. under N2, gives the blue selenoketone (2). On reaction with w-chloroperbenzoic acid, (2) is converted into di-r-butyl ketone and selenium. 

Azetidines. Reaction of 7-amino alcohols with triphenylphosphine dibromide and then with triethylamine first at 0° and then at 25° results in formation of triphenylphosphine oxide and N-substituted azetidines. This method had been used previously to prepare aziridines from 3-amino alcohols (3, 322). 

The higher nucleophilicity of phenoxide and perchlorobenzoate counterions causes immediate nucleophilic substitution on the corresponding phosphonium ion phenoxy group, giving triphenylphosphine oxide and either perchlorodiphenyl ether or pentachlorophenyl pentachlorobenzoate respectively (p. 324) (92). Similarly, the reaction of triphenylphosphine dibromide with excess of silver pentachlorobenzoate yields pentachlorobenzoic anhydride in quantitative yield (Veciana, 1977). 

When cholest-5-ene-3, 4 -diol (70) was heated with triphenylphosphine dibromide in DMF, 3-bromocholesta-3,5-diene (71) was obtained and also, unexpectedly, 2-formylcholesta-2,4,6-triene (72). The latter product apparently arises by a Vilsmeier reaction, presumably involving the reagent Me2N=CHBr cf. ref. 96). 

Olefin inversion. This inversion can be accomplished by epoxidation, reaction with triphenylphosphine dibromide or dichloride to give a ic-dihalide, and then /rans-elimination of the added halo groups with zinc-acetic acid (equation I). The sequence involves two inversions, one at each carbon joined to oxygen. ... 

An often used method for the preparation of carbodiirnides is the aza-Wittig reaction of an isocyanate with an uninophosphorane. The latter can he formed either from an amine and triphenylphosphine dibromide or from an azide and triphe-nylphosphine. 

An improved preparation of 1-deuteriated aldehydes of high isotopic purity is reported reaction of an aldehyde with triphenylphosphine dibromide in pyridine leads utimately to the salt (178), which is smoothly cleaved by deuterium oxide (Scheme 104). 

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