Electrochemical formal [3 + 2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines

Abstract

A catalyst-free electrochemical [3+2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines in absence of any external oxidant is developed for constructing 1,2,4-triazolidine skeleton, where 32 examples are displayed. The unique electrochemical cycloaddition...

Electrochemical Site-Selective Alkylation of Azobenzenes with (Thio)Xanthenes

“…Based on the above mechanistic experiments and previous reports [ 41 , 42 , 43 , 45 , 46 , 47 , 48 , 49 ], a possible reaction mechanism is proposed in Scheme 6 . Firstly, anodic oxidation of xanthene 2a led to the formation of intermediate I , which was further deprotonated to generate radical II , followed by an anode oxidation to form the cationic species III .…”

“…As a result, we speculate that electrochemistry maybe provides a unique opportunity to facilitate the functionalization of azobenzene. In a recent study, we disclosed an electrochemical formal [3 + 2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines, which afforded 1,2,4-triazolidine derivatives in an efficient fashion [ 41 ]. Based on these works, and our recent findings in electrochemical synthesis [ 41 , 42 , 43 ], we continue our effort to address the problem of para -position C–H functionalization in the azobenzenes with the electrochemical method.…”

“…In a recent study, we disclosed an electrochemical formal [3 + 2] cycloaddition of azobenzenes with hexahydro-1,3,5-triazines, which afforded 1,2,4-triazolidine derivatives in an efficient fashion [ 41 ]. Based on these works, and our recent findings in electrochemical synthesis [ 41 , 42 , 43 ], we continue our effort to address the problem of para -position C–H functionalization in the azobenzenes with the electrochemical method. Herein, we report a catalyst-free alkylation of azobenzenes with (thio)xanthenes enabled by electrochemistry, which affords a series of azobenzenes derivatives with high regioselectivity ( Scheme 1 E).…”

Catalyst-free inverse-electron-demand aza-Diels–Alder reaction of 4,4-dicyano-2-methylenebut-3-enoates and 1,3,5-triazinanes: access to polysubstituted tetrahydropyridines

“…7 In addition, they could also act as efficient and varying synthons for the construction of biologically important nitrogen-containing heterocycles through distinct annulation reactions. 8–11 Representative examples include [2 + n ], 8 [3 + n ], 8 a ,9 [4 + n ], 10 and [2 + 2 + n ] 11 annulations, in which two, three, four, or more atoms could be incorporated into the products. In regard to [2 + 4] annulation reactions using 1,3,5-triazinanes as two-atom synthon, there have been only five documents.…”

Cyclization of Azobenzenes Via Electrochemical Oxidation Induced Benzylic Radical Generation

“…Unfortunately, most of the previous work mainly relied on the use of toxic transition metals, chemical oxidants, or critical conditions limiting their scope and potential applications . To overcome these issues, based on our recent findings on electrosynthesis, we herein report a design involving an ortho -alkyl-substituted azobenzene, which could be used for benzylic C–H transformation via cyclization for heterocycle synthesis, such as indazoles (Scheme c). − In addition, anodic oxidation of benzylic C–H into ketones is almost unavoidable in the present electrochemical system, especially for the electron-rich arenes. Currently, addressing this issue remains a big challenge from a synthetic point of view, but the generated byproduct can be transformed into the same 2 H -indazole products by using the reductive cyclization method that was developed in our group, thus enabling the construction of 2 H -indazole backbone in a sustainable manner.…”