Unexpected course of reaction between (E)-2-aryl-1-cyano-1-nitroethenes and diazafluorene: why is there no 1,3-dipolar cycloaddition?

Abstract

Reactions between (E)-2-aryl-1-cyano-1-nitroethenes and diazafluorene lead to acyclic 2,3-diazabuta-1,3-diene derivatives, instead of the expected pyrazoline systems. DFT calculations suggest that this is a consequence of formation of zwitterionic structure in the first stage of the reaction. It must be noted that this is a specific property of the (E)-2-aryl-1-cyano-1-nitroethenes group, in contrast to most other conjugated nitroalkenes.Graphical abstract Electronic supplementary materialThe online version of this article (doi:10.1007/s00706-016-1893-5) contains supplementary material, which is available to authorized users.

Competition between [2 + 1]- and [4 + 1]-cycloaddition mechanisms in reactions of conjugated nitroalkenes with dichlorocarbene in the light of a DFT computational study

“…On the other hand, earlier reports [42] suggest a stepwise mechanism, with zwitterionic intermediate. It should be additionally underlined that stepwise mechanisms have been recently documented based on comprehensive experimental and quantum-chemical studies regarding a group of different type cycloadditions involving conjugated nitroalkenes [35,43,44]. Therefore, neither one-step nor stepwise mechanisms can be excluded a priori for the reactions studied (Scheme 2).…”

A DFT computational study on the [3+2] cycloaddition between parent thionitrone and nitroethene

“…It was found previously that the B3LYP/6-31G(d) calculations illustrate well the structure of TSs in [3+2] cycloadditions involving conjugated nitroalkenes. [23][24][25][26] The critical points on reaction paths were localized in an analogous manner as in the case of the previously analyzed reaction of diazafluorene with cyanonitroethenes. 26 In particular, for structure optimization of the reactants and the reaction products the Berny algorithm was applied.…”

A Full Regioselective and Stereoselective Synthesis of 4‐Nitroisoxazolidines via Stepwise [3 + 2] Cycloaddition Reactions between (Z)‐C‐(9‐Anthryl)‐N‐arylnitrones and (E)‐3,3,3‐Trichloro‐1‐nitroprop‐1‐ene: Comprehensive Experimental and Theoretical Study

“…However, it should be noted, that kinetic studies and density functional theory (DFT) calculations indicate that aforementioned reactions () proceed by a polar mechanism, with a highly asynchronous transition state. But in no instance, this is a stepwise mechanism, examples of which have been recently described in the previous literature . In the other hand, stepwise mechanism is more probably in reactions involving nitrones 2a–c owing to steric hindrance on C‐atom of CNO moiety.…”