Theoretical investigation of Banert cascade reaction

Abstract

Computational inside of Banert cascade reaction for triazole formation is studied with B3LYP/6-31G(d,p) level of theory. The reaction proceeds mainly by SN2 initial chloride displacement rather than SN2′-type attack. Furthermore, according to the rate of reaction calculation, SN2 displacement is much faster than SN2′ displacement in the order of 8. The [3,3]-sigmatropic rearrangement for the conversion of propargyl azide into triazafulvene has been proved as the rate-determining step having highest activation energy parameter. Solvent effect on total course of reaction has been found negligible. Furthermore, effects of different density functional theory functionals and functional groups on activation energies of [3,3]-sigmatropic rearrangement of propargyl azide were also studied. BHHLYP, ωB97XD, M062X and BMK calculated ΔG‡ are consistent with B3LYP.

Divergent Mechanisms of the Banert Cascade with Propargyl Azides

“…For the azides investigated here, neither the allenyl azide nor the triazafulvene intermediate were directly observed as an intermediate by 1 H NMR. This is consistent with a computational model of this cascade, which predicts a rate determining barrier for the initial sigmatropic process (Scheme , [3,3]) and a fast electrocyclization (Scheme a, step i) …”

Allylic azides: synthesis, reactivity, and the Winstein rearrangement

“…This is followed by a 6-π electrocyclization and a nucleophilic trap to generate NH-1,2,3-triazoles. 239 Recently, Sharpless and co-workers explored this rearrangement and developed a general method for generating NH-1,2,3trizoles (Scheme 45b). 240 Substituted 1,2,3-triazoles can be generated via a CuAAC reaction, but using HN 3 would be unappealing to generate NH-1,2,3-trizoles.…”

Understanding the Fate of the Banert Cascade of Propargylic Azides. Sigmatropic versus Prototropic Pathway

“…32,33 Currently, only one theoretical study about the sigmatropic pathway mechanism of the Banert cascade has been reported. 34 In that work, the [3,3]-sigmatropic rearrangement for the conversion of propargylic azide into triazafulvene has been proved as the rate determining step. Therefore, we wanted to study the Banert cascade to provide the theoretical basis of the reaction mechanism.…”