Formation of 3-Methylene-1,4-cyclohexadienes from<i>α</i>,<i>α</i>,<i>α</i>′,<i>α</i>′-Tetraaryl-1,4-benzenedimethanols by the Intramolecular Migration of an Aryl Group
作者:Masanori Wada、Wen-hao Wei、Katsuhiko Kirishima、Satoko Natsume、Tatsuo Erabi
DOI:10.1246/bcsj.70.1413
日期:1997.6
By reactions of diethyl p-phthalate with 2,6-dimethoxyphenyllithium, ΦLi, a tri-substituted compound, p-HOCΦ2C6H4C(O)Φ (1), or tetra-substituted 1,4-benzenedimethanol, p-HOCΦ2C6H4CΦ2OH (2a), were obtained. Compound 1 further reacted with aryllithium, ArLi, to give the 1,4-benzenedimethanols, p-HOCΦ2C6H4CArΦOH (Ar = 4-MeC6H42b, 4-MeOC6H42c). When 2a was treated with acid in dimethyl sulfoxide, 3-(2,6-dimethoxybenzoyl)-3-(2,6-dimethoxyphenyl)-6-[bis(2,6-dimethoxyphenyl)methylene]-1,4-cyclohexadiene, (4a) was obtained in quantitative yield under a variety of conditions. The reaction is understood to involve an initial formation of carbenium ion, [p-Φ2C+–C6H4CΦ2OH] (3a), of which the positive charge must be partly shared with the other end of the p-phenylene ring, where one of the neighboring Φ-groups migrates. Reactions in acetone resulted to give 4a or dark-violet crystals of (2′,6′-dimethoxy-4-biphenylyl)bis(2,6-dimethoxyphenyl)carbenium perchlorate, [(4-ΦC6H4)CΦ2]ClO4, depending on the reaction conditions. Reactions in methanol, ethanol, or in hot 2-propanol resulted to give the reduced compound, (4-ΦC6H4)Φ2CH. The 1,4-benzenedimethanols, 2b and 2c, also reacted with perchloric acid in dimethyl sulfoxide to form the 3-methylene-1,4-cyclohexadiene derivatives, (Ar = 4-MeC6H44b, 4-MeOC6H44c), respectively. Evidence is given by the 1H NMR spectrum, which shows the formation of intermediate carbenium ions 3a—c.
通过二乙基对苯二甲酸酯与2,6-二甲氧基苯基锂反应,得到了三取代化合物p-HOCΦ₂C₆H₄C(O)Φ (1)或四取代的1,4-苯二醇p-HOCΦ₂C₆H₄CΦ₂OH (2a)。化合物1进一步与芳基锂ArLi反应,生成1,4-苯二醇p-HOCΦ₂C₆H₄CArΦOH(Ar = 4-MeC₆H₄₂b, 4-MeOC₆H₄₂c)。当2a在二甲基亚砜中与酸反应时,得到了3-(2,6-二甲氧基苯甲酰基)-3-(2,6-二甲氧基苯基)-6-[双(2,6-二甲氧基苯基)亚甲基]-1,4-环己二烯(4a),在多种条件下以定量产率获得。该反应被认为涉及初始形成碳正离子[p-Φ₂C⁺–C₆H₄CΦ₂OH] (3a),该正电荷部分需与p-苯基环的另一端共享,其中一个相邻的Φ基团迁移。丙酮中的反应根据反应条件产生4a或深紫色结晶的(2′,6′-二甲氧基-4-联苯基)双(2,6-二甲氧基苯基)碳正离子高氯酸盐[(4-ΦC₆H₄)CΦ₂]ClO₄。在甲醇、乙醇或热2-丙醇中的反应产生了还原化合物(4-ΦC₆H₄)Φ₂CH。1,4-苯二醇2b和2c也分别与高氯酸在二甲基亚砜中反应,形成3-亚甲基-1,4-环己二烯衍生物(Ar = 4-MeC₆H₄₄b, 4-MeOC₆H₄₄c)。1H NMR光谱提供了证据,显示了中间碳正离子3a—c的形成。