NBS allylic bromination of cyclohexene

NBS allylic bromination of cyclohexene; 3-Bromocyclohexene SyntheticPage 144 (2001) Submitted 28th Aug 2001, published 28th Aug 2001 Andrew McCarroll (kafy3@sussex.ac.uk), A contribution from the Walton group Group, St Andrews Chemicals Used Cyclohexene, N-Bromosuccinimide, Benzoyl peroxide, Carbon tetrachloride Procedure Benzoyl peroxide (0.35 g) was added to a mixture of cyclohexene (35 g; 0.43 mol) and N-bromosuccinimide (24.9 g; 0.14 mol) in carbon tetrachloride (100 cm3). The mixture was stirred for 2 hours, then heated slowly to reflux, and maintained at reflux for 3.5 hours. The mixture was cooled, filtered and concentrated, then distilled at reduced pressure (b.p. 61 oC @ 12 mmHg) to give 3-bromocyclohexene as a colourless oil (15.71 g; 70%). Author's Comments Unfortunately, carbon tetrachloride is the only suitable solvent. The slow start to the reaction is necessary, as it can go out of control if heated too rapidly. The method is a good one for symmetric molecules. Regioselectivity can be poor if the allylic positions are not equivalent. We only performed this reaction once. Data 1H nmr (CDCl3) 1.60-2.35 (6H, m), 4.85 (1H, m), 5.75-6.00 (2H, m) Lead Reference A. J. McCarroll, PhD Thesis, University of St Andrews, 2000. Other References B. S. Furniss, A. J. Hannaford, P. W. G. Smith and A. R. Tatchell, "Vogel's Textbook of Organc Chemistry, 5th Edition," Longman, Harlow, 1989.