Phenyltrimethylammonium tribromide

The metal catalyst is not absolutely required for the aziridination reaction, and other positive nitrogen sources may also be used. After some years of optimization of the reactions of alkenes with positive nitrogen sources in the presence of bromine equivalents, Sharpless et al. reported the utility of chloramine-T in alkene aziridinations [24]. Electron-rich or electron-neutral alkenes react with the anhydrous chloramines and phenyltrimethylammonium tribromide in acetonitrile at ambient temperature, with allylic alcohols being particularly good substrates for the reaction (Schemes 4.18 and 4.19). 

Two methods that are particularly convenient for large-scale synthesis of aziridines are discussed below. Both utilize readily available chloramine salts, such as chloramine-T, as sources of nitrogen. The first method involves direct olefin azir-idination catalyzed by phenyltrimethylammonium tribromide (PhNMe3+Br3 PTAB) [42]. In the second method, 1,2-hydroxysulfonamides, conveniently obtained by osmium-catalyzed aminohydroxylation of olefins, are converted into aziridines by one-pot cyclodehydration. 

As these solid agents, some quaternary ammonium tribromides such as pyridinium hydrobromide perbromide (ref. 1), phenyltrimethylammonium tribromide (ref. 2), tetramethylammonium tribromide (ref. 3), and tetrabutyl-ammonium tribromide (ref. 4) have already been reported as mild and selective brominating agents (Fig. 1). 

Phenyltrimethylammonium sulfo-methylate, 53, 111 Phenyltrimethylammonium tribromide, selective bromina-tion with, 53, 112, 114 4-Phenylurazole, from 4-phenyl-1-carbethoxysemicarbazide and potassium hydroxide,... 

Tosylhydrazones react with phenyltrimethylammonium tribromide under phase-transfer catalysed basic conditions to yield, initially, a-bromo- and derivatives which, under the basic conditions, eliminate one equivalent of HBr to yield unstable 2-tosylazopropenes [27]. 

The bromination-dehydrobromination route is in many cases preferable [Scheme 2 80JCS(P1)2081], using bromine, N-bromosuceinimide (NBS), or phenyltrimethylammonium tribromide (PTAB). The resulting mono-bromo, geminal, or vicinal dibromo and tribromo derivatives (e.g., 5a,b) are often preferentially dehydrobrominated by Jones method [73JCS(P1)968] using lithium salts in dimethylformamide (DMF). Bases such as triethyla-mine, sodium methoxide, and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were also used. 

Although it is more usual to obtain the halogenoacyl derivatives of pyrrole and indole by direct acylation (see Section 3.05.1.2.6), it is possible to carry out electrophilic halogena-tion of acylindoles <79HC(25-3)357). 3,4-Diacetyl-l,2,5-trimethylpyrrole has also been reported to react with phenyltrimethylammonium tribromide to give the 3,4-bis(bromoacetyl) derivative, which cyclizes in the presence of a zinc-copper catalyst to yield 4,5,6,7-tetrahydro-l,2,3-trimethyl-4,7-dioxoisoindole (74CC1034). 

SELECTIVE a-BROMINATION OF AN ARALKYL KETONE WITH PHENYLTRIMETHYLAMMONIUM TRIBROMIDE 2-BROMOACETYL-6-METHOXYNAPHTHALENE AND 2,2-DIBROMOACETYL-6-METHOXYNAPHTHALENE... 

B. Phenyltrimethylammonium Tribromide. A solution of 10 g. (0.04 mole) of phenyltrimethylammonium sulfomethylate in 10 ml. of aqueous 48% hydrobromic acid diluted with 10 ml. of water is prepared in a 125-ml. Erlenmeyer flask equipped with a magnetic stirrer. Bromine (2.5 ml.) (Note 5) is added to the stirred solution from a dropping funnel in about 20 minutes. An orange-yellow precipitate forms immediately and the slurry is stirred at room temperature for 5-6 hours. The product, phenyltrimethylammonium tribromide (PTT) is filtered, washed with about 10 ml. of water and air-dried under an efficient hood. The crude PTT, ca. 15 g., is recrystallized from 25 ml. of acetic acid to give, after filtration and air-drying, 12.9-14.0 g. (86-93%) (Note 6) of orange crystals, m.p. 113— 115°. 

Bromination-desilylbromination of fS-silyl ketones. The preliminary work on protection of oc,/ -enones by this sequence (8, 196-197) has been perfected in several respects1 and shown to be generally applicable to synthesis of oy8-enones.2 Either bromine or phenyltrimethylammonium tribromide (PTAB, 1,855 2,328 4, 386) can be used. In either case, bromine is introduced mainly at the a-position adjacent to the /1-silyl group. Surprisingly, the undesired a -bromo-/(-silyl ketone is converted to the a-bromo-/)-silyl ketone on exposure to hydrogen bromide at 20°. No other acids can clTccl this conversion. Desilylbromination is generally effected with DBU or F". The sequence is applicable to synthesis of a-methylene ketones (equation I) and lactones. 

Although the reaction in Scheme 10 is a highly efficient procedure, a two-step process was required to prepare aziridines from olefins. Two more convenient methods for the one-step aziridination using CT were discovered by the authors in 1998, one of which involves the iodine-catalyzed aziridination of unfunctionalyzed olefins with CT trihydrate [7b] (Scheme 11). The bromine-catalyzed aziridination of unfunctionalyzed olefins and allylic alcohols with anhydrous CT was reported at the same time [7c], though in this case phenyltrimethylammonium tribromide (PTAB), and not Br2, was used as a catalyst (Scheme 12). These two reactions are applicable to a wide range of olefins, and are considered to proceed by almost the same pathway. 

Fleck coupling of styrenes with 3-bromo-2-styrylchromones, prepared by concomitant cyclisation and bromination of the Baker-Venkataraman derived l,5-diarylpenta-2,4-dien-l-ones with phenyltrimethylammonium tribromide, provides a useful route to 2,3-diarylxanthones (Scheme 38) <07SL3113>. 

A rapid method for resolving ( + )-carvone through the derivative (151) has been described. Reaction of carvone with allyl Grignard reagents leads to the expected products (152), and these can be aromatized with toluene-p-sulphonic acid to (153) and (154). An improved method for the preparation of carvone 1,3,8-tribromide [(155) see Vol. 1, p. 31] consists in treating the dibromide (156), obtained by Wallach from dihydrocarvone (148), with phenyltrimethylammonium tribromide in tetrahydrofuran. ... 

Scheme 18.32 and a wide range of cocatalysts including the commonly tested tetrabutylammonium halides (F-, Cl-, Br- and I-) and iV,iV -dimethyl-aminopyridine as well as the remarkable phenyltrimethylammonium tribromide (PTAT [PhMe3N] [Br3] ). The combination Al(TPP)Cl and phe-nyl-trimethyl ammonium tribromide produced cyclic carbonates in excellent yields, this combination displaying the best compromise between the Lewis acidity of the centre, the leaving ability of the axial halide and the nucleo-philicity of the anion in the cocatalyst. PTAT showed a better activity than the tetrabutylammonium halides, whereas the neutral DMAP delivered the worst conversion of this series. ... 

A soln. of 6-benzoyl-2-dimethylamino--4,5-dihydro-6H-pyrrolo[3,2-e]benzothiazole in tetrahydrofuran treated with phenyltrimethylammonium tribromide in the same solvent, and the product isolated after 2 hrs. 6-benzoyl-2-dimethylamino-6H-... 

Nafion-H has been used as a catalyst for the preparation of 1,1-diacetates from aldehydes and acetic anhydride. High yields were obtained in short reaction times at room temperature. Acetals of aromatic aldehydes may be prepared under non-acidic conditions by treatment of aldazines with phenyliodosyl diacetate in alcoholic solution. When [Ayrfrojcy- Hlmethanol is used as solvent, deuterium is incorporated at the aldehydic position. a-Monobromoacetalization may be carried out conveniently using phenyltrimethylammonium tribromide in ethylene glycol and tetrahydrofuran. ... 

Preparation by reaction of phenyltrimethylammonium tribromide on 4-hydroxy-a-bromo-acetophenone [4403]. 

Preparation by bromination of 4-hydroxyacetophenone in acetic acid (63%) [4422] or in a mixture of ethyl ether and chloroform [4413] according to [4414]. Preparation by Fries rearrangement of phenyl bromoacetate with aluminium chloride without solvent between 120° and 140° (40%) [4415], (30%) [4416]. Preparation by reaction of tetrabutylammonium tribromide, benzyltrimethylam-monium tribromide or phenyltrimethylammonium tribromide on 4-hydroxyacetophenone in tetrahydrofuran [4403]. 

DMAP = N,N-dimethylaminopyiidine, DMF = N -dimethylformamide, DCM = dichloromethane, PTAT = phenyltrimethylammonium tribromide, EO = ethylene oxide, PO = propylene oxide, ECH = epichlrohydrin, SO = styreneoxide, AGH = allylicglycidil ether. BO = butylene oxide, HO = n-hexene oxide, DO = N-decene oxide, PPO = 2-phenylpropylene oxide, PS-DFILX = polymer supported diol functionalized ionic liquids, acac = acetyl acetonate, CIL= carboxylic-acid functionalized imidazolium-based ILs, note active site consideration for TOP calculation is not uniform. Co-valent triazine complexes... 

On one hand, in 1998, Sharpless and coworkers reported a positive bromine-catalyzed aziridination of alkenes using anhydrous chloramine-T with a wide scope of alkenes (Scheme 2.30) [48]. As a result of extensively screening of bromine sources such as ZnBr2, HgBr2, and Br2, they found that phenyltrimethylammonium tribromide (PhNMe3" Br3 PTAB) most efficiently catalyzed the aziridination among tested. 

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