A formal [3 + 3] cyclization reaction
of diaziridines and quinones
has been developed offering 1,3,4-oxadiazinanes in generally high
yields (up to 96%). The reaction was catalyzed by Sc(OTf)3 with a large substrate scope for both diaziridines and quinones.
The synergistic activation of 1,3-dipolar diaziridines and the dipolar
quinones was found to be essential to enable this reaction.
A three-component cascade reaction comprising cyclic ketones, arylamines, and benzoylmethylene malonates has been developed to access 4,5,6,7-tetrahydro-1H-indoles. The reaction was achieved through cooperative enamine-Brønsted catalysis in high yields with wide substrate scopes. Mechanistic studies identified the role of the Brønsted acid catalyst and revealed the formation of an imine intermediate, which was confirmed by X-ray crystallography.
The formation of enamine from primary
arylamines was detected and
confirmed by nuclear magnetic resonance spectroscopy. The presence
of a radical quencher, e.g., (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl,
was found to be essential for the detection of enamine formation.
A direct synthesis of α-enaminones from primary arylamines and
ketones was also developed. Mechanistic investigation of α-enaminone
formation suggests that an amine radical cation generated through
O2 singlet energy transfer was involved in initiating α-enaminone
formation. The reactivity and utility of α-enaminones were explored
with a [3+3] cycloaddition reaction of enones affording dihydropyridines
in good yields (58–85%). α-Enaminones displayed a set
of reactivities that is different from that of enamines. The knowledge
gained in this work advances our basic understanding of organic chemistry,
providing insights and new opportunities in enamine catalysis.
Cooperative enamine‐metal Lewis acid catalysis has emerged as a powerful tool to construct carbon‐carbon and carbon‐heteroatom bond forming reactions. A concise synthetic method for asymmetric synthesis of chromans from cyclohexanones and salicylaldehydes has been developed to afford tricyclic chromans containing three consecutive stereogenic centers in good yields (up to 87 %) and stereoselectivity (up to 99 % ee and 11 : 1 : 1 dr). This difficult organic transformation was achieved through bifunctional enamine‐metal Lewis acid catalysis. It is believed that the strong activation of the salicylaldehydes through chelating to the metal Lewis acid and the bifunctional nature of the catalyst accounts for the high yields and enantioselectivity of the reaction. The absolute configurations of the chroman products were established through X‐ray crystallography. DFT calculations were conducted to understand the mechanism and stereoselectivity of this reaction.
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.