Recent advance in transition-metal-catalyzed oxidant-free 4+1 annulation through C–H bond activation

4+1 annulation based reaction offers a versatile tool for the synthesis of 5-membered carbo/heterocycles. Recent advances of 4+1 annulation through transition-metal-catalyzed C–H bond activation have provided straightforward and widely applicable alternatives to the traditional methods. In particular, the redox-neutral strategies emerged in the past 5?years overcome the inherent disadvantages caused by the external oxidant which are generally required in the early protocols to regenerate the active catalyst, such as limited substrate scope, harsh reaction conditions and generation of stoichiometric by-products. Progress in oxidant-free 4+1 annulations through transition-metal-catalyzed C–H bond activation are discussed in this review until September 2017.     

Silver-catalyzed [3+2+1] annulation of aryl amidines with benzyl isocyanide

A silver-catalyzed [3+2+1] annulation of amidines with benzyl isocyanide toward 2,4-diaryl-1,3,5-triazines was developed. A variety of symmetrical and unsymmetrical products were obtained in moderate to good yields. This work also features an oxidant-free approach to 2,4-disubstituted triazines.     

Electrochemical synthesis of 3-azido-indolines from amino-azidation of alkenes

An electrochemical amino-azidation of 2-aminostyre ne with sodium azide(NaN_3) was developed,which can be carried out smoothly in water under metal-free condition,affording a series of 3-azido indolines with high yields.     

Solvent-free multicomponent synthesis of 2-arylpyridines using p-sulfonic acid calix[6]arene as a reusable catalyst

An efficient methodology for obtaining 2-arylpyrimidines based on the use of p-sulfonic acid calix[6]arene as an organocatalyst is proposed. The methodology involves the formation of 1,2-dihydropyridine intermediates using a variety of aromatic aldehydes with methyl or ethyl acetoacetate and ammonium acetate, which are the same starting materials as in the Hantzsch reaction, under solvent-free reaction conditions, at 25 °C, followed by air oxidation for 12 h. The catalyst efficiency is not compromised after its successive use in reactions. Eleven examples were obtained with very good to excellent yields of 2-arylpyridines (92–62%). This is the first report about the use of calixarenes as catalysts in the multicomponent synthesis of 2-arylpyridines (molecules with potential biological activity).     

无金属和氧化剂温和条件下碱促进的烯胺酮碳-碳双键断裂合成NH2-结构脒类化合物

报道了室温条件下烯胺酮和磺酰叠氮通过碳-碳双键断裂合成N-磺酰基醚类化合物的方法.反应在1,8-二.氮杂双环[5.4.0]十一碳-7-烯(DBU)存在下进行,无需使用任何金属和氧化剂,具有良好的底物适用性.烯胺酮上的15N同位素标记实验证实,磺酰叠氮仅作为产物中的磺酰胺片段供体,同时,该实验也有力地支持反应机理涉及关键的1,2,3-三唑啉中间体的原位形成以及环分解.     

Cobalt-catalyzed electrochemical CH/NH functionalization of N-(quinolin-8-yl)benzamide with isocyanides

An efficient synthesis of functionalized iminoisoindolinone derivatives has been achieved via a mild electrochemical oxidative CH/NH functionalization/intramolecular annulations with isocyanides in undivided cell equipped with a nickel cathode. In the presence of earth abundant cobalt catalyst, versatile iminoisoindolinone derivatives obtained in good yields and in a sustainable manner by using electricity as an oxidant in place of stoichiometric amount of silver and copper salts.