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Synlett 2006(3): 0498-0499  
DOI: 10.1055/s-2006-926262
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

N-Bromosuccinimide - A Selective, Mild Substitute for Bromine

Taraknath Kundu*
Department of Chemistry, Bose Institute, 93/1, A.P.C. Road, ­Kolkata 700 009, India
e-Mail: taraknath_kundu@yahoo.co.uk;

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Publikationsdatum:
06. Februar 2006 (online)

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Biographical Sketches

Taraknath Kundu was born in 1977 in Kolkata, India. He obtained M.Sc. in Chemistry with specialisation in organic chemistry from the University of Calcutta and qualified in the National Eligibility Test (CSIR-UGC-NET) in 2001. He is currently working for his Ph.D. under the supervision of Prof. Manas Chakrabarty at Bose ­Institute, India. His research interest involves the development of new syntheses of heterocycles.

Introduction

N-Bromosuccinimide (NBS) is commercially available but can also be prepared from succinimide by bromination under alkaline conditions. It is used as a mild source of bromine with higher selectivity, primarily due to its ­property of releasing of bromine in a low, steady-state concentration. [1] It is most widely used for benzylic and ­allylic brominations in the presence of a catalytic amount of a free-radical initiator such as benzoyl peroxide or AIBN in CCl4. [2a] However, benzylic bromination in the absence of any free-radical initiator was recently achieved under microwave irradiation (MWI) in solid phase. [2b] The free-radical condition is also reported to bring about Z- to E-alkene isomerisation. [2c] Cook and co-workers demonstrated the regioselectivity of bromination by NBS under different conditions with indoles. [2a] In many instances, NBS has been used as an activator, for example in stereoselective glycosidation, [3a] protection [3b] and deprotection of ketals [3c] or THP ethers, [3d] and in the synthesis of diindolyl­alkanes. [3e] NBS is also widely used as a mild oxidant [4] as well as for oxidative cyclisations. [5] Recently, NBS was used for the mild, regioselective bromination of ­(hetero)aromatics in ionic liquid, [6a] [b] or for α-bromination of carbonyl compounds in the presence of NaHSO4-SiO2, [6c] or TMSOTf. [6d]

Abstracts

(A) Chakrabarty et al. recently reported the formation of an ­enamide double bond under benzylic bromination conditions with NBS in a concise synthesis of coscinamide B, an anti-HIV bis­indolic enamide. [7]

(B) Oxidation of indoles to isatins has also been accomplished by NBS; the reaction is thought to proceed via a 3,3-dibromooxindole as an intermediate. [8a] Indeed, Fuchs and Funk have isolated and used a 3-alkyl-3-bromooxindole as a key intermediate in the ­elegant syntheses of ()-flustramines A and C, [8b] and ()-perphoramidine. [8c]

(C) Decarboxylative bromination with NBS in the presence of LiOAc under MWI has provided a stereoselective synthesis of (E)-β-arylvinyl bromides by a Hunsdiecker-type reaction. [9]

(D) Recently, NBS was used to catalyse both hydroamination and hydroalkoxylation of activated styrenes to afford amino and ether derivatives, respectively. [10]

(E) Interestingly, NBS, along with DBU, promotes the cyclisation of N-alkylthioureidoindoles and alkyl N-(indol-5′-yl)dithiocarbamates to furnish only the corresponding 2-alkylamino- and 2-alkylthiothiazolo[5,4-e]indoles, regioselectively. [11]

(F) NBS has also found application in the oxidative cycloamination of olefins with aziridines for the synthesis of saturated ­nitrogen-contaning heterocycles. [12]

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