TY - JOUR A1 - Mazzanti, Virginia A1 - Cacciarini, Martina A1 - Broman, Søren L. A1 - Parker, Christian R. A1 - Schau-Magnussen, Magnus A1 - Bond, Andrew D. A1 - Nielsen, Mogens B. T1 - On the bromination of the dihydroazulene/vinylheptafulvene photo-/thermoswitch JF - Beilstein Journal of Organic Chemistry PY - 2012/// VL - 8 SP - 958 EP - 966 SN - 1860-5397 DO - 10.3762/bjoc.8.108 PB - Beilstein-Institut JA - Beilstein J. Org. Chem. UR - https://doi.org/10.3762/bjoc.8.108 KW - azulene KW - bromination KW - dihydroazulene KW - molecular switches KW - photoswitch KW - vinylheptafulvene N2 - Background: The dihydroazulene (DHA)/vinylheptafulvene (VHF) system (with two cyano groups at C1) functions as a photo-/thermoswitch. Direct ionic bromination of DHA has previously furnished a regioselective route to a 7,8-dibromide, which by elimination was converted to a 7-bromo-substituted DHA. This compound has served as a central building block for functionalization of the DHA by palladium-catalyzed cross-coupling reactions. The current work explores another bromination protocol for achieving the isomeric 3-bromo-DHA and also explores the outcome of additional bromination of this compound as well as of the known 7-bromo-DHA.Results: Radical bromination on two different VHFs by using N-bromosuccinimide/benzoyl peroxide and light, followed by a ring-closure reaction generated the corresponding 3-bromo-DHAs, as confirmed in one case by X-ray crystallography. According to a 1H NMR spectroscopic study, the ring closure of the brominated VHF seemed to occur readily under the reaction conditions. A subsequent bromination–elimination protocol provided a 3,7-dibromo-DHA. In contrast, treating the known 7-bromo-DHA with bromine generated a very labile species that was converted to a new 3,7-dibromoazulene, i.e., the fully unsaturated species. Azulenes were also found to form from brominated compounds when left standing for a long time in the solid state. Kinetics measurements reveal that the 3-bromo substituent enhances the rate of the thermal conversion of the VHF to DHA, which is opposite to the effect exerted by a bromo substituent in the seven-membered ring.Conclusion: Two general procedures for functionalizing the DHA core with a bromo substituent (at positions 3 and 7, respectively) are now available with the DHA as starting material. ER - TY - JOUR AU - Daub, J. AU - Knöchel, T. AU - Mannschreck, A. JF - Angew. Chem., Int. Ed. Engl. PY - 1984/// VL - 23 SP - 960 EP - 961 DO - 10.1002/anie.198409601 ER - TY - CHAP AU - Mrozek, T. AU - Ajayaghosh, A. AU - Daub, J. T2 - Optoelectronic Molecular Switches Based on Dihydroazulene-Vinylheptafulvene (DHA-VHF) T1 - Molecular Switches PY - 2001/// SP - 63 EP - 106 DO - 10.1002/3527600329.ch3 PB - Wiley-VCH CY - Weinheim A2 - Feringa, B. L. ER - TY - JOUR AU - Nielsen, M. B. 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