Diastereoselective cycloaddition of tosylpropadiene to azomethine ylides, derived from proline and carbonyl compounds: an experimental and DFT study

Abstract

Upon heating methanol solutions, tosylpropadiene cycloadds to proline-derived ylides with the formation of pyrrolidine adducts as single diastereomers in 16–37% yields. The observed diastereo- and regioselectivity is reasoned by a concise DFT study.

Graphical Abstract

Keywords:

• 1,3-dipolar cycloaddition
• allenes
• azomethine ylides
• diastereoselective
• DFT

Acknowledgments

This research made use of resources from the Centre for Magnetic Resonance and Centre for Chemical Analysis and Materials of Saint-Petersburg State University. Lozovskiy S.V. strongly appreciates moral and financial help of Professor Vasilyev A.V., along with his critical opinion. This research was financially supported by the grant of the Russian Science Foundation, RSF 20-15-00332.

Notes

1 During 2020-2021 years more than 150 peer-reviewed publications were devoted to the use of azomethine ylides^1–6 in fine organic synthesis, of which more than 30 are diastereoselective 3 + 2 cycloadditions. - Scifinder data, date of search and reference retraction is 07/07/2021

2 That is necessary for stabilisation of anionic fragment of TS, i.e., ^δ-C-EWG fragment

3 Used level of theory: for thermodynamic and preliminary calculations – HF/3-21G (these are geometries, thermodynamic and electronic values, shown in the main text), for reliability check – B3LYP/6-31G (with and without PCM solvent) and M06/cc-pvdz. For detailed study see SI. Recently, the use of low-cost levels of calculations of cycloadditions shown to be useful³³.

4 Other non-aromatic carbon AOs deposits are smaller, this MO mostly delocalised on ipso-, ortho- and para- atoms of aromatic ring (56%).

5 This additional ring formation in TS1 was found in all levels of theory used, for geometries see SI.