An enamine method for the synthesis of 1-azaazulene derivatives. Reactions of troponimines with enamines 1
作者:Tohru Takayasu、Makoto Nitta
DOI:10.1039/a809700c
日期:——
A short new synthesis of 1-azaazulene derivatives consists of the enamine alkylation of troponimines 4–7 with pyrrolidino enamines, which are derived from cycloalkanones, aliphatic ketones, and heterocyclic ketones, to lead to formal [8 + 2] cycloadducts and subsequent aromatization under the reaction conditions. The reactions are quite general, and N-hydroxy- and N-methoxytroponimines, 4 and 5, are less reactive than N-mesyloxy- and N-tosyloxytroponimines, 6 and 7, which react smoothly even at room temperature. In the reaction of the pyrrolidino enamine, which is derived from cyclopentanone, forcing conditions are required, probably because of ring strain in the [8 + 2] cycloadduct 11a. Furthermore, in the reactions of 4–7 with isomeric mixtures of two pyrrolidino enamines, 15/16 and 20/21, only enamines 15 and 20 can intervene in the cycloaddition reactions, giving 1-azaazulene derivatives. In the context of the reactivity of 4–7 and pyrrolidino enamines, and the selectivity observed in the reactions with isomeric mixtures of enamines, minimal neglect of differential overlap (MNDO) calculations on troponimines 4–7 and pyrrolidino enamines, as well as isomeric mixtures of two enamines, 15/16 and 20/21, were performed to gain further insight into the reactions via a theoretical interpretation based upon frontier molecular orbital theory (FMO). Troponimines 6 and 7 have lower LUMOs and they are more reactive than troponimines 4 and 5; the energy level of the HOMO of the pyrrolidino enamine derived from cyclopentanone is relatively higher as compared to those of other pyrrolidino enamines. Enamines 15 and 20 are less stable and energy levels of the HOMOs are higher as compared with those of the corresponding isomers 16 and 21, respectively.
一种新的短链合成1-氮基藍烯衍生物的方法包括对4-7号烃基化的氨基萘酮与源自环烷酮、脂肪酮和杂环酮的吡咯烯胺进行反应,从而产生形式上的[8 + 2]环加成物,并在反应条件下随后发生芳香化。这些反应相当普遍,其中N-羟基和N-美克酮基的氨基萘酮4和5的反应性较低,而N-美克酯基和N-苯磺酯基的氨基萘酮6和7则在室温下也能顺利反应。在从环戊酮衍生的吡咯烯胺的反应中,需采取强迫条件,这可能是由于[8 + 2]环加成物11a的环应变。此外,在4-7号与两种异构体的吡咯烯胺混合物15/16和20/21反应时,只有吡咯烯胺15和20能参与环加成反应,生成1-氮基蓝烯衍生物。针对4-7号和吡咯烯胺的反应性,以及在与异构体的吡咯烯胺混合物反应中观察到的选择性,进行了最小忽略微分重叠(MNDO)计算,以进一步深入理解反应,通过基于前沿分子轨道理论(FMO)的理论解释。氨基萘酮6和7的低空态分子轨道(LUMO)更低,反应性比氨基萘酮4和5更强;源自环戊酮的吡咯烯胺的高占据分子轨道(HOMO)能量水平相对较高。吡咯烯胺15和20相对不稳定,其高占据分子轨道的能量水平较对应异构体16和21更高。