A-bromo imidate

Many of the reactions of A-chloro- and A-bromo-imides are extremely violent or explosive. Those observed include A-chlorosuccinimide with aliphatic alcohols or benzylamine or hydrazine hydrate A-bromosuccimmidc with aniline, diallyl sulfide, or hydrazine hydrate or 3-nitro-A-bromophthalimide with tetrahydrofur-furyl alcohol l,3-dichloro-5,5-dimethyl-2,4-imidazolidindione with xylene (violent explosion). Individually indexed compounds are ... 

The thermally or photochemically activated addition of cyclic A-bromo imides to alkenes, particularly to cyclohexene, is inefficient, even when diastereoselective63-66,141. However, A-bromo phthalimide reacted readily with 2,3-dihydrofuran to give the regioisomers 2 and 3, and with 3,4-dihydro-2//-pyran to give 4 regioselectively in satisfactory yield141. The franv-diastereomers were formed predominantly, especially in the case of the six-membered cyclic compound 4. 

Enolate Halogenation. Enolate halogenation is achieved by reaction of the boryl enolate with N-Bromosuccinimide, affording configurationally stable a-bromo imides in >94 6 diastere-... 

In certain cases, allylsilanes and trimethylsilyl enol ethers react with alkyl halides with the formation of a new carbon-carbon bond. a-Bromo imidates (eq 8) and p-chloro imines have been reported to undergo electrophilic aromatic substitution on relatively electron-rich aromatics in the presence of AgBp4. 

Oxazol-4-ones 132 have been prepared by Trost and co-workers via a microwave-assisted cyclocondensation of bromo imides in the presence of NaF [86]. These products where then employed for a Mo-catalyzed asymmetric synthesis of Q -hydroxycarboxylic acid derivatives 134 (Scheme 47). 

A simple two-step synthesis of 5H-alkyl-2-phenyloxazol-4-ones has been reported by Trost and coworkers (Scheme 6.209) [377]. a-Bromo acid halides were condensed with benzamide in the presence of pyridine base at 60 °C to form the corresponding imides. Microwave irradiation of the imide intermediates in N,N-dimethylacetamide (DMA) containing sodium fluoride at 180 °C for 10 min provided the desired 5H-alkyl-2-phenyloxazol-4-ones (oxalactims) in yields of 44—82%. This class of heterocycles served as excellent precursors for the asymmetric synthesis of a-hydroxycar-boxylic acid derivatives [377]. 

This same group also investigated the thermolysis of ot-bromo amidines as a means to prepare 2-alkoxy-4(5/7)-oxazolones. Here, an ot-bromo imide 195a or 195b was converted to the corresponding amidine 196a or 196b, which upon... 

The pyrazino[2,3-chlorosuccin-imide to the give 6-bromo and 6-chloropyrazinothiadiazines 34 <1999JME1698>. 

Selected examples are given in Table 9 for bromofluorinations of alkenes using A-bromosuccin-imide in combination with 70% hydrogen fluoride/pyridine (Method A) and hydrogen fluo-ride/polyvinylpyridine (Method B), respectively. Table 10 shows examples of the selective monoaddition of in situ produced halofluorides (70 % hydrogen fluoride/pyridine and A-iodo-. A-bromo- or /V-ehloro-succinimide) to symmetrically substituted alkynes. 

Boron trifluoride and boron trifluoride-diethyl ether complex can be used as a source of fluoride ions in the presence of hypobromites and hypochlorites, e.g. methyl hypobromitc, tert-butyl hypobromite, methyl hypochlorite in carbon tetrachloride at 25 C. The addition of bromine monofluoride" and chlorine monofluoride" to various alkenes is accompanied by the formation of the corresponding alkoxybromides and alkoxychlorides which hinder the isolation of the halofluorinated products.57 jV-Bromo- and A -chloro-substiluted alkyl- and arylamines. -amides, and -imides, A -chloro-A,-methylamine, A -bromo-A -methylamine, A -chloro-A, /V-dimethylamine, A-bromo-A.A-dimethylamine, ACV-dichloro-A -methylamine, V,fV-dibromo-,V-mcthylaminc, A -bromosuccinimide, -V-chlorosuccinimide, Af-bromoacct-amide, A.A -dichlorourethane, can be used in the reaction instead of the hypohalites. The reactions with various alkenes conducted in dichloromethane at room temperature in the presence of boron trifluoride-diethyl ether complex produce bromofluoro and chlorofluoro addition products in 40-80 % yield. However, the reactions are complicated by the addition of A -halo-succinimides and Af.A-dichlorourcthane to the C = C bonds.58... 

A-Haloamides and imides are a most versatile group of halogenating reagents. They are normally prepared in an aqueous solution by reaction of the parent amide/imide with the corresponding hypohalite. An improved method for the synthesis of A-bromo amides/imides has recently been published, in which the parent compounds are oxy-brominated in aqueous solution by a mixture of HBr/NaBr03 or NaBr/NaBr03/H2S04 (equation 95)700. 

Yet a further reaction which forms three bonds is the use of imidic esters with suitably functionalized ketones (e.g. a-hydroxy, a-bromo). This method is exemplified by the synthesis of a new imidazole alkaloid (146), which had been isolated from a member of the Urticaceae family (80AHC(27)24l), and by the more general synthesis of 4-alkyl-5-methoxymethylimidazole (147) (79AP107). The cyclization process, which takes place in liquid ammonia, may be complicated by 2-alkylbutanamide by-products which result from Favorskii rearrangement of the bromomethoxy ketones (Scheme 83). 

A general two-step method has been developed for the synthesis of 5//-5-alkyl-2-phenyloxazoM-ones 251. This procedure involves the initial condensation of a-bromo acid halides 249 with benzamide to form an imide intermediate 250 followed by microwave-mediated cyclization in the presence of NaF to give the corresponding 4(5//)-oxazolones 251 (Scheme 73) <2004JA1944>. 

The interactions of 2-hydroxy- or a-bromo- ketones and an imidic ester are exemplified by the synthesis of a new imidazole alkaloid (4) which had been isolated from the Urticaceae family (see Scheme 1). The reaction of a-bromoketone, ammonia, and an aldehyde gives imidazoles. " ... 

The synthesis of the antibiotic anisomycin (160) provides another example of the efficient alkylation of a thioamide with an a-bromoarylacetate. Thiolactam (154) was alkylated with a-bromo ester (155) followed by sulfide contraction to generate the vinylogous carbamate (156) in good yield (Scheme 33). In contrast, initial attempts to condense the imidate of the dimethoxylactam (161) with various aryl components (162) met with failure that was attributed to the steric hindrance created by the alkoxy groups (Scheme 34). The vinylogous carbamate (156) was converted to the acid, which decarboxylated to the enamine (157). Reduction yielded a 70 30 mixture of pyrrolidines (158) and (159) and the latter was converted to anisomycin. 

A Reformatsky type of reaction has been utilized in a novel route to /3-lactams, by allowing carbodi-imides and a-bromo-esters to react in the presence of zinc metal.Cyanuric chloride has been shown to activate the... 

Recommended reagents for mild dehydrogenation of primary and secondary alcohols are A-bromoacetamide45 5 and A-bromosuccinimide,456 also the A-halo imides A-bromophthalimide, A-chlorosuccinimide, isocyanuric bromide and chloride, and A-bromohexanolactam. These differ in oxidizing activity under comparable conditions A-chlorosuccinimide and isocyanuric chloride have greater efficiency than isocyanuric bromide but less than A-bromo-acetamide. Because of the mildness of the conditions required they find particular use in stereoselective oxidation of steroid alcohols.455... 

The ability to form stable salts of under the action of base is an important property of imides of perfluorocarboxylic acids. Henne and Zimmer used generated in situ silver salts of 46 and 47 for the preparation of the corresponding A -bromo deriva-... 

Maeda, M. Abe, M. Kojima, M. Bromofluorination of double bonds using N-bromo imides and tetrabutylammonium fluoride as a source of fluoride. J. Fluorine Chem. 1987,... 

In general, bromohydantoins, most other A-halo imides (A-bromo glutarimide, A-bromo-phthalimide, tetramethyl-A-bromosuccinimide, etc...except for A-iodosuccinimide), Br2, BrCCU, and A-bromocaprolactam are suitable reagents for radical brominations of allylic and benzylic substrates. Of all of these reagents, the most used reagents are NBS and Br2. 

Yang and coworkers used the a-bromo propionic imide 328 for a diastereoselective Reformatsky reaction that was mediated by diethyl zinc under catalysis of Ni(acac)2 and permitted to use aryl alkyl ketones as the carbonyl components. The... 

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