Direct access to 2-aryl substituted pyrrolinium salts for carbon centre based radicals without pyrrolidine-2-ylidene alias cyclic(alkyl)(amino)carbene (CAAC) as a precursor† ‡

Abstract

A new strategy to synthesise 2-substituted pyrrolinium salts.

Abstract

The synthesis of organic radicals is challenging due to their inherent instability. In recent years, cyclic(alkyl)(amino)carbene (CAAC)-derived 2-substituted pyrrolinium salts have been used as synthons for the synthesis of isolable carbon-based radicals. Herein, we report a direct, easy and convenient method for the synthesis of 2-aryl substituted pyrrolinium salts without using CAAC as a precursor. These cations can be reduced to the corresponding radicals. The influence of the aryl substituent at the C-2 position on radical stabilization and dimerization has been investigated. Because of the large scope of our strategy (capability to modulate different substituents at all the C- and N-centres of the pyrrolinium salts), it has the merit to be an extremely effective and productive route for generating carbon-based radicals whose stability as well as reactivity can be varied.

Notes

†Dedicated to Professor Vinod K. Singh on the occasion of his 60th birthday.

‡Electronic supplementary information (ESI) available: Experimental details, NMR spectra, X-ray crystallographic data and theoretical details. CCDC 1868053 ( 3 ^H ), 1868056 ( 3 ^Me ), 1868057 ( 3 ^Et ), 1868055 ( 3 ^{t Bu} ) and 1868054 ( 3 ^{H ₂} ). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc05477k