Ring-Closure Reactions of 1,2-Diaza-4,5-benzoheptatrienyl Metal Compounds: Experiment and Theory

2-Alkenylbenzylidene hydrazones 5a−m, which are accessible in good to excellent yields in a four-step synthesis, are converted into 1,2-diaza-4,5-benzoheptatrienyl metal compounds 1a−m by treatment with KO-t-Bu as base. These metal compounds undergo the various types of reactions in good yields and exclusively depending on the nature of substituents R1 and R3. Thus, metal compounds 1a−c carrying alkyl substituents R1 and R3 form 3H-benzodiazepines 6a−c after electrophilic quench of the intermediate cyclic anion 7 in a 7-endo-trig electrocyclic reaction with a möbius aromatic transition structure 1−-TS. Similarly, a benzothienyl derivative 5n is converted into diazepine 6d. Potassium compounds 1d−h, which are N-methyl and aryl substituted at R3, form 1,2-dihydrophthalazines 8a−e in a predominantly charge-controlled 6-exo-trig cyclization reaction. In contrast, aryl−aryl-substituted systems 5i−m did not lead to cyclic products upon deprotonation, but the intermediate open-chain metal compounds 1i−m were trapped by acid chlorides at N1 to yield the hydrazides 10a−e. We interpret thermodynamics and kinetics of these reactions in the context of the Baldwin rules on the basis of quantum chemical calculations and discuss the transition structures considering the results of NICS and NBO-charge calculations. Examples of the products 6, 8, and 10 could be characterized by X-ray diffraction.

2-烯基亚苄基腙类化合物5a~m可通过四步合成以良好至优异的收率制备得到，经强碱叔丁醇钾（KO-t-Bu）处理后，可转化为1,2-二氮杂-4,5-苯并庚三烯基金属化合物1a~m。这类金属化合物的反应类型与收率表现完全取决于取代基R1与R3的性质。因此，带有烷基取代基R1和R3的金属化合物1a~c，在中间体环状阴离子7经亲电淬灭后，通过具有莫比乌斯芳香过渡态（möbius aromatic transition structure 1−-TS）的7-内环型三中心电环化反应，生成3H-苯并二氮杂䓬类化合物6a~c。类似地，苯并噻吩基衍生物5n可转化为二氮杂䓬6d。在R3位带有N-甲基与芳基取代的钾化合物1d~h，则主要通过电荷控制的6-外环型三中心环化反应，生成1,2-二氢酞嗪类化合物8a~e。与之相反，芳基-芳基取代的体系5i~m在去质子化后并未生成环状产物，但其中间体开链金属化合物1i~m可在N1位点被酰氯捕获，进而得到酰肼类化合物10a~e。本研究基于量子化学计算，结合布朗德规则（Baldwin rules）阐释了上述反应的热力学与动力学机制，并结合核独立化学位移（NICS）与自然键轨道电荷（NBO-charge）计算结果，对过渡态结构展开了讨论。产物6、8及10的代表性样品可通过X射线衍射（X-ray diffraction）进行结构表征。