- Efficient and complementary methods offering access to synthetically valuable 1,2-dibromobenzenes
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1,2-Dibromobenzenes are highly valuable precursors for various organic transformations, in particular, reactions based on the intermediate formation of benzynes. This report describes short sequences for the synthesis of various derivatives based on regioselective bromination, ortho-metalation, and halogen/metal permutations. 1,2-Dibromo-3-iodobenzene (2f), 1,2-dibromo-4- iodobenzene (4c), and 2,3-dibromo-1,4-diiodobenzene (5e) act as intermediates in these syntheses. Bromo-iodoarenes have been synthesized by short and regioselective bromination or iodination sequences that combine ortho-metalation, halo-desilylation, diazotation, or bromination reactions of anilines. These polyhalo derivatives were then used as key intermediates to access a wide range of functionalized 1,2-dibromobenzenes by chemoselective organometallic reactions. Copyright
- Diemer, Vincent,Leroux, Frederic R.,Colobert, Fracoise
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p. 327 - 340
(2011/02/26)
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- The photochemistry of polyhaloarenes XIII. The photohydrodehalogenation of 3,4-dibromobiphenyl
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Irradiation of 3,4-dibromobiphenyl (BpBr2) in acetonitrile resulted in the formation of 4-bromobiphenyl (BpBr) and 3- bromobiphenyl (3-BpBr) in a ratio of 7.6 ± 0.1 up to 22% conversion of starting material. The dependence of the reciprocal of the quantum yield (1/Φ) upon 1/BpBr2 is linear. Reduction of BpBr2 with lithium di-tert-butylbiphenylide generates a 3.6:1.0 ratio of BpBr to 3-BpBr, while photohydrodebromination of BpBr2 in the presence of triethylamine produces a similar ratio of 1.8:1.0. Product determining radical stability was assessed by radical debromination of BpBr2 using Ph3SnH in THF, which resulted in a BpBr:3-BpBr ratio of 1.5:1.0 AMI calculations on the product determining radicals provide the basis for rationalization of products via excimer and radical anion intermediates.
- Freeman, Peter K.,Jang, Jung-Suk,Haugen, Christian M.
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p. 8397 - 8406
(2007/10/03)
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- Synthetically Useful Aryl-Aryl Bond Formation via Grignard Generation and Trapping of Arynes. A One Step Synthesis of p-Terphenyl and Unsymmetric Biaryls
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A one-pot route to p-terphenyls is described.Addition of 1,4-dibromo-2,5-diiodobenzene, 1, to excess aryl Grignard reagent gives the terphenyl di-Grignard 2 and the trihalo mono-Grignard 5.After aqueous quench, p-terphenyls are isolated in 30percent to 50percent yield (Table I).This yield can be improved to 70-80percent by adding potassium tert-butoxide or lithium tetramethylpiperidide to the reaction mixture prior to workup.Mechanisms involving organometallic aryne intermediates are proposed.With o-bromoiodoarenes in place of tetrahaloarenes the method can be adapted to prepare unsymmetric biaryls in good yield (Table II).
- Hart, Harold,Harada, Katsumasa,Du, Chi-Jen Frank
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p. 3104 - 3110
(2007/10/02)
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