The diverser eactivity of N-heterocyclic carbenes (NHCs) in organocatalysis is due to the possibility of different modeso fa ction. Although NHC-bounde nolates and dienolates are known, the related NHC-bound cross-conjugated aza-trienolates remain elusive. Herein,w ed emonstrate the NHC-catalyzed formal [6+ +2] annulation of nitrogen-containing heterocyclic aldehydes with a,a,a-trifluoroacetophenones leadingt ot he 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.Scheme1.Generation and reaction of various NHC-enolates.
Although NHC-catalyzed
umpolung of imines are known, the related
reactions under oxidative conditions are limited. Described herein
is the two-step process involving the initial formation of aldimines
from the corresponding aldehydes and 2-amino benzyl alcohols followed
by NHC-catalyzed cyclization proceeding via the imidoyl azoliums under
oxidative conditions. The reaction allowed the synthesis of trifluoromethylated
3,1-benzoxazines in good yields and broad scope. The role of NHC in
the intramolecular cyclization and preliminary mechanistic experiments
are also provided.
This communication reports the use of a rigid organic scaffold to attach two unsymmetrical peptide chains on a single carbon atom. The approach describes the step‐by‐step attachment of peptide chains to the rigid dimedone template (5,5‐dimethyl‐1,3‐cyclohexanedione) – a molecular scaffold that directs orientation of the peptide helices in a well‐defined arrangement via intra‐molecular hydrogen bonding. The overall topology of the final molecules was studied using CD spectroscopy which suggested existence of helical architecture.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.