N‐Heterocyclic Carbenes as Key Intermediates in the Synthesis of Fused, Mesoionic, Tricyclic Heterocycles

Idir Benaissa (1) , Lenka Pallova (1) , Marie‐emilie Morantin (1) , Thomas Lafitte (1) , Mathieu Huynh (1) , Cécile Barthes (1) , Laure Vendier (1) , Noël Lugan (1) , Stéphanie Bastin (1) , Vincent César (1)

1 LCC - Laboratoire de chimie de coordination

Coupling between 5-bromoimidazo[1,5-a]pyridinium salts and malonate or arylacetate esters leads to a facile and straightforward access to the new mesoionic, fused, tricyclic system of imidazo[2,1,5-cd]indolizinium-3-olate. Mechanistic studies show that the reaction pathway consists of nucleophilic aromatic substitution on the cationic, bicyclic heterocycle by an enolate-type moiety and in the nucleophilic attack of a transient free N-heterocyclic carbene (NHC) species on the ester group; the relative order of these two steps depends on the nature of the starting ester. This work highlights the valuable implementation of free NHC species as key intermediates in synthetic chemistry, beyond their classical use as stabilizing ligands or organocatalysts.

Domaines: Chimie de coordination

Idir Benaissa, Lenka Pallova, Marie‐emilie Morantin, Thomas Lafitte, Mathieu Huynh, et al.. N‐Heterocyclic Carbenes as Key Intermediates in the Synthesis of Fused, Mesoionic, Tricyclic Heterocycles. Chemistry - A European Journal, 2019, 25 (56), pp.13030-13036. ⟨10.1002/chem.201903242⟩. ⟨hal-02338944⟩