Organoboranes for synthesis. 10.1 the base-induced reaction of bromine with organoboranes. A convenient procedure for the conversion of alkenes into alkyl bromides via hydroboration |
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| Affiliation: | 1. FP-ENAS-Faculdade de Ciências de Saúde, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Carlos da Maia, 296, P-4200-150 Porto, Portugal;2. REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal;3. Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland;4. Instituto de Tecnologia em Fármacos e Farmanguinhos, Fundação Oswaldo Cruz, 21041-250 Rio de Janeiro, RJ, Brazil;1. Cancer Research Institute, BMC, Slovak Academy of Sciences, Dubravska cesta 9, 845 05 Bratislava, Slovak Republic;2. Institute of Experimental Endocrinology, BMC, Slovak Academy of Sciences, Dubravska cesta 9, 845 05 Bratislava, Slovak Republic;1. College of Chemistry and Pharmaceutical sciences, Qingdao Agricultural University, Qingdao 266109, PR China;2. Center for Bioengineering and Biotechnology, College of Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, PR China;3. State Key Laboratory of Crystal Materials, Shandong University, Jinan 250204, PR China;1. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, Okólna str. 2, 50-950 Wrocław, Poland;2. Faculty of Chemistry, Opole University, Oleska str. 48, 45-052 Opole, Poland |
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| Abstract: | The reaction of trialkylboranes with bromine is greatly accelerated by base. Bromination in the presence of sodium hydroxide provides alkyl bromide along with a large amount of the corresponding alcohol. The use of sodium methoxide as a base eliminates this undesirable sidereaction and provides an improved yield of alkyl bromide. Consequently, hydroboration, followed by bromination in the presence of sodium methoxide, provides a convenient new procedure for the conversion of alkenes into alkyl bromides. The organoboranes, obtained via hydroboration of terminal alkenes, react with the utilization of all three alkyl groups attached to boron, providing nearly quantitative yields of alkyl bromides. This procedure also accommodates common organic functional groups, as demonstrated by the preparation of methyl 11-bromoundecanoate and 11-bromoundecyl acetate from the corresponding functionally substituted alkenes. Under these conditions, secondary and bulky primary alkyl groups react more sluggishly. However, a procedure involving simultaneous addition of bromine and methanolic sodium methoxide provides improved results for such derivatives. Surprisingly, the base-induced bromination of tri-exo-norbomylborane results in an inversion of configuration at the reaction center to give predominantlyendo-2-bromonorbomane. A mechanism is proposed to account for this remarkable inversion. |
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