Succinimide, N-bromo-

Replacement of the proton on nitrogen in succinimide by bromine gives N bromo succinimide a reagent used for allylic and benzylic brominations (Sections 10 4 and 1112)... 

IKROMOHYDRINS FROM ALKENES AND N-BROMO-SUCCINIMIDE IN DIMETHYL SULFOXIDE erythro-2-BROMO-l,2-DIPHENYLETHANOL... 

The suspension may be warmed to dissolve the alkene more rapidly. (E)-Stilbene dissolves completely at ca. 65°. If the suspension is warmed, it must be cooled below 30° before proceeding further to prevent a vigorous reaction when the N-bromo-succinimide is added. The submitters recommend that the warm suspension be cooled under an atmosphere of nitrogen. If a volatile alkene is used, the mixture should be cooled prior to and during the addition of N-bromosuccinimide to prevent losses by evaporation. 

Another reagent that is extremely useful synthetically is N-bromo-succinimide (NBS, 85), which is highly selective in attacking only weak C—H bonds, i.e. at allylic, benzylic, etc., positions. It requires the presence of radical initiators, and has been shown to effect bromination through providing a constant, but very low, ambient concentration of Br2—this is maintained through reaction of the HBr produced in the reaction with NBS (c, below). TTiere is usually a trace of Br2 or HBr in the NBS that can react with the initiator to generate the initial Br to start reaction (a, below) ... 

Kojic acid was brominated at position 6 with bromine water4 the 2-(chloromethyl) derivative of kojic acid was brominated with N-bromo-succinimide,87 and chlorinated with sulfuryl chloride and aluminum chloride,88 in both cases probably at C6. The C-benzoylation89 and C-acetylation90 of kojic acid, likewise at C6, was accomplished by Woods using a modification of the Friedel-Crafts reaction. The 2-carboxyethyl side chain was introduced at C6 in a reaction with 2-bromopropionic acid.91... 

Scheme 13.15 Preparation of oxygen-substituted VCPs 142 (Eq. 1) and 163 (Eq. 2). Conditions (a) Na metal, TMSCI, Et20, A (b) MeOH, RT (c) vinylmagnesium bromide, EtjO, 0°C to RT (d) TBSOTf, 2,6-lutidine, CHjCb, RT (e) N-bromo-succinimide, 2-methoxyethanol, -78 °C to RT (f) KOH, RT to 90°C (g) 1.3 equiv. CH2I2, Zn metal, CuCI, AcCI, EtjO, A.

Fluorination of vinorelbine was thus performed in super acid medium (HF-SbFs). A super electrophilic agent, such as a chloromethyl or a Br+ cation is generated in s/fu from a chloromethane (CHCI3, CCI4) or from N-Bromo Succinimide (NBS). It is able to abstract a hydrogen from the protonated alkaloid, leading to a cation that can be trapped by an halide anion present in the medium [105,106], Difluorination remarkably occurs selectively at C-4 of the clavamine fragment (Fig. 37) [105]. 

The key step in their-approach was asymmetric photoisomerization of the a, 3-unsaturated (Z)-ketone precursor 103b in diethyl ( + )-Lg-tartrate. The bromide 103a obtained by N-bromo-succinimide bromination of the (Z)[8.8] precursor 64b, was converted into the a,P-unsaturated (Z)-ketone 103b by the routine synthetic procedures. Irradiation in a hexane solution with a medium pressure Hg lamp effected the photoisomerization of the (Z)-precursor 103b to afford a 1 5.5 mixture of (Z)-( )[8.8] ketones. After these preliminary experiments, a neat solution of 103 b in diethyl ( + )-Lg-tartrate was irradiated for 3 h. Preparative GLC of the resulting 1 7 mixture of (Z) and ( )[8.8] ketones produced a 38 % yield of ( )[8.8] ketone 104 enriched in the (—)-enantiomer, [a]n4 —13° (hexane). 

Benzylic halides can be prepared by the same radical-halogenating agents that give allylic halides from alkenes. These include Cl2, Br2, N-bromo-succinimide (Section 14-3A), S02C12, and im-butyl hypochlorite (see Exercise 4-18) ... 

Saigusa and Oda (196) have brominated polystyrene with N-bromo-succinimide in the presence of benzoyl peroxide 61% of the styrene units were brominated in the main chain. After dehydrohalogen-ation with sodium butoxide, the polymer contains 39% unchanged styrene units, 49% unsaturated groups, -CH=C-, and about 12%... 

Pyridinium poly(hydrogen fluoride)-N-Bromo succinimide, 454-455 a-Pyridones, 50... 

In a number of reactions that are written as dissociative electron attachments, short-lived radical anions are in fact intermediates. A case in point is 5BrUra (Chap. 10). An interesting behavior is shown by the radical anion of N-bromo-succinimide which does not release a bromide ion but rather fragments into a bromine atom and a succinimide anion [reactions (17) and (18)] (Lind et al. 1991). 

The most efficient photosubstitution reaction, with many applications in synthesis, is the photobromination method developed by FERRIER s group [24]. The substitution of H-5 is regioselective and stereoselective for pentopyranosides [25], hexo-pyranosides [26], 1-6 anhydrosugars [27], uronic acids [24, 28] heterocyclic derivatives from deoxyinosones [29], nucleosides [30, 31], etc.. . using bromine or N-bromo-succinimide in carbon tetracloride under irradiation. 

Bosch (130) has published a spectrophotometric determination of vitamin Bg, and other vitamins, in pharmaceutical preparations with N-bromo-succinimide, in methanol at 370-380 nm. The method allows determination of 100-1000 yg of vitamin Bg. Vitamin Bj, B], A, and menadione bisulphite interfere with this method. 

Treatment of this aromatic heterocycle with NBS (N-bromo-succinimide) and AIBN gives mainly one product but this is difficult to purify from minor impurities containing one or three bromine atoms. Further treatment with 10% aqueous NaOH gives one easily separable product in modest yield (50%). What are the mechanisms for the reactions What might the minor products be ... 

Methylthiomethyl ethers are comparable in stability to alkoxymethyl ethers towards strongly basic conditions or mild acid. For example, methylthiomethyl ethers survive aqueous acetic acid under conditions that hydrolyse TBS ethers, dioxolanes or tetrahydropyranyl protectors. They can be removed under rather specific and mild conditions that do not affect most acetal-type protectors such as MEM. MOM. etc. (see above). The presence of the sulfur makes this group liable to oxidation by strong oxidants such as peracids. Cr(VI), and N-bromo-succinimide, and it will poison Pd catalysts. The methylthiomethyl group was First introduced by Corey and co-workers586 and its virtues exploited by them in a synthesis of the antibiotics Erythronolide587 588 and Brefeldin.589... 

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