N‐Heterocyclic Carbene‐Catalyzed Formal [6+2] Annulation Reaction via Cross‐Conjugated Aza‐Trienolate Intermediates

Kuruva Balanna , Krishnaprasad Madica , Subrata Mukherjee (1) , Arghya Ghosh , Thomas Poisson (2) , Tatiana Besset (2) , Garima Jindal , Akkattu Biju

1 Department of Theoretical and Applied Mechanics [Ithaca]
2 COBRA - Chimie Organique et Bioorganique : Réactivité et Analyse

The diverse reactivity of N‐heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modes of action. Although NHC‐bound enolates and dienolates are known, the related NHC‐bound cross‐conjugated aza‐trienolates remain elusive. Herein, we demonstrate the NHC‐catalyzed formal [6+2] annulation of nitrogen‐containing heterocyclic aldehydes with α,α,α‐trifluoroacetophenones leading to the formation of versatile pyrrolooxazolones (29 examples). The catalytically generated cross‐conjugated aza‐trienolates (aza‐fulvene type) underwent smooth [6+2] annulation with electrophilic ketones to afford the product in moderate to good yields under mild conditions. Preliminary DFT studies on the mechanism are also provided.

Domains: Chemical Sciences; Chemical Sciences; Organic chemistry

Kuruva Balanna, Krishnaprasad Madica, Subrata Mukherjee, Arghya Ghosh, Thomas Poisson, et al.. N‐Heterocyclic Carbene‐Catalyzed Formal [6+2] Annulation Reaction via Cross‐Conjugated Aza‐Trienolate Intermediates. Chemistry - A European Journal, 2019, 26 (4), pp.818-822. ⟨10.1002/chem.201905177⟩. ⟨hal-02455771⟩