Access to Imidazole Derivatives by Silver(I) Carbonate Mediated Coupling of Vinyl Azides with Secondary Amines

Diastereoselective Formation of Quaternary Stereocenters in Imidazole N-Oxide Cycloaddition with Fluoroalkenes

Imidazole N-oxides are attractive starting materials for the preparation of complex molecules containing an imidazole ring. Dipolar cycloaddition between 1,1-difluoroalkenes and imidazole N-oxides bearing a chiral auxiliary performed in the presence of oxygen or nitrogen nucleophiles was found to provide access to esters and amides bearing a 2-azaheteroaryl substituent at the α position of the imidazole ring as mixtures of diastereomers that, in most cases, are readily separable. This three-component reaction introduces a new tertiary or quaternary all-carbon stereocenter into the heterocyclic ring at a position originally occupied by hydrogen. Importantly, products containing a trifluoromethyl group attached to this stereocenter are readily available as well.

Vinylazides: versatile synthons and magical precursors for the construction of N-heterocycles

Nowadays, application of vinylazides as precursors is a key method for the construction of N-heterocycles in organic synthesis. These versatile three-atom synthons can be converted into intermediates such as 2H-azirines, iminyl radicals, iminyl metal complexes, iminyl inions and nitrilium ions that subsequently afford a wide range of polyfunctional cyclic nitrogen-containing compounds. In this review, the reactions of vinylazides leading to these products (in the last decade) are categorized based on the types of the resulting N-heterocyclic rings and a brief and concise description of the reaction mechanisms is presented.

Visible-Light-Induced Deaminative Alkylation/Cyclization of Alkyl Amines with N-Methacryloyl-2-phenylbenzoimidazoles in Continuous-Flow Organo-Photocatalysis

Herein, we present a metal-free visible-light-induced eosin-y-catalyzed deaminative strategy for the sequential alkylation/cyclization of N-methacryloyl-2-phenylbenzoimidazoles with alkyl amine-derived Katritzky salts, which provides an efficient avenue for the construction of various benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-one derivatives in moderate to excellent yields under mild reaction conditions. The key enabling feature of this novel reaction includes utilization of redox-active pyridinium salts from abundant and inexpensive primary amine feedstocks that were converted into alkyl radicals via C-N bond scission and subsequent alkylation/cyclization with N-methacryloyl-2-phenylbenzoimidazoles by the formation of two new C-C bonds. In addition, we implemented this protocol for a variety of amino acids, affording the products in moderate yields. Moreover, the novel, environmentally benign batch protocol was further carried out in a continuous-flow regime by utilizing a perfluoroalkoxy alkane tubing microreactor under optimized reaction conditions with a blue light-emitting diode light source, enabling excellent yields and a shorter reaction time (19 min) versus the long reaction time (16 h) of the batch reaction. The reaction displays excellent functional group tolerance, easy operation, scalability, mild reaction conditions, and broad synthetic utility.

α-Substituted vinyl azides: an emerging functionalized alkene

Vinyl azides are highly versatile synthons that provide access to numerous N-heterocycles and other functional groups.