Understanding the 1,3-Dipolar Cycloadditions of Allenes

Song Yu, Pascal Vermeeren, Kevin van Dommelen, F. Matthias Bickelhaupt*, Trevor A. Hamlin

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We have quantum chemically studied the reactivity, site-, and regioselectivity of the 1,3-dipolar cycloaddition between methyl azide and various allenes, including the archetypal allene propadiene, heteroallenes, and cyclic allenes, by using density functional theory (DFT). The 1,3-dipolar cycloaddition reactivity of linear (hetero)allenes decreases as the number of heteroatoms in the allene increases, and formation of the 1,5-adduct is, in all cases, favored over the 1,4-adduct. Both effects find their origin in the strength of the primary orbital interactions. The cycloaddition reactivity of cyclic allenes was also investigated, and the increased predistortion of allenes, that results upon cyclization, leads to systematically lower activation barriers not due to the expected variations in the strain energy, but instead from the differences in the interaction energy. The geometric predistortion of cyclic allenes enhances the reactivity compared to linear allenes through a unique mechanism that involves a smaller HOMO–LUMO gap, which manifests as more stabilizing orbital interactions.

Original languageEnglish
Pages (from-to)11529-11539
Number of pages11
JournalChemistry - A European Journal
Volume26
Issue number50
Early online date27 Mar 2020
DOIs
Publication statusPublished - 4 Sep 2020

Keywords

  • 1,3-dipolar cycloadditions
  • activation strain model
  • allenes
  • density functional theory calculations
  • reactivity

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