Protonation-induced Cyclization of 1,8-Bis(arylethynyl)anthraquinones: Monopyrylium Salt Formation and Intensification of Donor–Acceptor Interaction
作者:Koya Prabhakara Rao、Mio Kondo、Ryota Sakamoto、Tetsuro Kusamoto、Shoko Kume、Hiroshi Nishihara
DOI:10.1246/cl.2011.1456
日期:2011.12.5
We previously reported protonation-induced double cyclization reaction of 1,4-Ar2Aq and 1,5-Ar2Aq (Ar2Aq: bis(arylethynyl)anthraquinone) with strong acid HX that generated the corresponding dipyrylium salts [1,4-Ar2Pyl2]X2 and [1,5-Ar2Pyl2]X2. In this communication we disclose the protonation reactions of 1,8-Fc2Aq (Fc: ferrocenyl), 1,8-Am2Aq (Am: 4-N,N-bis(4-methoxyphenyl)aminophenyl), and 1,8-AmFcAq, which is the first example of heterodonor molecules in the Ar2Aq series, and synthesized by means of stepwise Sonogashira–Hagihara cross-coupling reactions. In contrast to the 1,4-Ar2Aq and 1,5-Ar2Aq series, 1,8-Ar2Aq undergoes protonation-induced single cyclization, so that it is converted into the corresponding monopyrylium salt [1,8-Ar2Pyl]X. [1,8-Ar2Pyl]X features an extremely small HOMO–LUMO gap (0.50–0.73 V), ascribable to the significant lowering of the LUMO level upon the pyrylium formation.
我们以前曾报道过 1,4-Ar2Aq 和 1,5-Ar2Aq (Ar2Aq:双(芳基乙炔基)蒽醌)与强酸 HX 的质子化诱导双环化反应,生成了相应的二吡啶鎓盐 [1,4-Ar2Pyl2]X2 和 [1,5-Ar2Pyl2]X2。在这篇通讯中,我们披露了 1,8-Fc2Aq(Fc:二茂铁基)、1,8-Am2Aq(Am:4-N,N-双(4-甲氧基苯基)氨基苯基)和 1,8-AmFcAq 的质子化反应,这是 Ar2Aq 系列中第一个异配位体分子的实例,是通过逐步的 Sonogashira-Hagihara 交叉偶联反应合成的。与 1,4-Ar2Aq 和 1,5-Ar2Aq 系列不同,1,8-Ar2Aq 会发生质子化诱导的单环化反应,从而转化为相应的单吡喃盐 [1,8-Ar2Pyl]X。[1,8-Ar2Pyl]X 具有极小的 HOMO-LUMO 间隙(0.50-0.73 V),这是因为形成吡鎓时 LUMO 水平显著降低。