An efficient method for the synthesis of imidazo[1,5-a]quinoxalines from 3-acylquinoxalinones and benzylamines via a novel imidazoannulation

The reaction of 3-aroylquinoxalin-2(1H)-ones and their N-alkyl analogues with benzylamines in DMSO proceeds through an intermediate formation of N-(α-quinoxalinylbenzylydene)benzylamine, which when subjected to oxidative cyclocondensation gives imidazo[1,5-a]quinoxalines. Applying this new approach of imidazoannullation to the bis-3-aroylquinoxalines makes it possible to develop fundamentally new methods of the synthesis of bis-imidazo[1,5-a]quinoxalines with the use of different benzylamines and heteromacrocycles with the 1,3-bis(3-arylimidazo[1,5-a]quinoxalin-1-yl)benzene structural fragment when m-xylylenediamine is used.     

Bridgehead Bicyclo[4.4.0]boron Heterocycles: A One‐Pot Four‐Component Synthesis of Dibenzo[e,i][1,3,7,2]oxadiazaborecin‐8(7H)‐ones

A one‐pot four‐component synthesis of 6‐aryl‐6H‐dibenzo[e,i][1,3,7,2]oxadiazaborecin‐8(7H)‐ones is described. Heating a mixture of isatoic anhydride and a benzylamine afforded the corresponding anthranilamide derivative, which was condensed with a 2‐hydroxybenzaldehyde and an arylboronic acid under solvent‐free conditions to produce bridgehead bicyclo[4.4.0]‐boron heterocycles in good to excellent yields. Single‐crystal X‐ray analysis conclusively confirms the structures of the obtained bridgehead bicyclic 6–6 heterocyclic compounds.     

Intermolecular Enantioselective Benzylic C(sp3)−H Amination by Cationic Copper Catalysis**

Chiral benzylic amines are privileged motifs in pharmacologically active molecules. Intramolecular enantioselective radical C(sp³)−H functionalization by hydrogen-atom transfer has emerged as a straightforward, powerful tool for the synthesis of chiral amines, but methods for intermolecular enantioselective C(sp³)−H amination remain elusive. Herein, we report a cationic copper catalytic system for intermolecular enantioselective benzylic C(sp³)−H amination with peroxide as an oxidant. This mild, straightforward method can be used to transform an array of feedstock alkylarenes and amides into chiral amines with high enantioselectivities, and it has good functional group tolerance and broad substrate scope. More importantly, it can be used to synthesize bioactive molecules, including chiral drugs. Preliminary mechanistic studies indicate that the amination reaction involves benzylic radicals generated by hydrogen-atom transfer.     

Enantioselective Intermolecular Radical Amidation and Amination of Benzylic C−H Bonds via Dual Copper and Photocatalysis

A method for direct access to enantioenriched benzylic amides and carbamate-protected primary benzylamines by C−H functionalization is reported. The C−H substrate is used as limiting reagent with only a small excess of the unactivated amide or carbamate nucleophile. The enantioselective intermolecular dehydrogenative C−N bond formation is enabled by a combination of a chiral copper catalyst, a photocatalyst, and an oxidant, and it takes place under mild conditions, which allow for a broad substrate scope. The method is compatible with late-stage C−H functionalization, and it provides easy access to ¹⁵N-labeled amides and amines starting from cheap ¹⁵NH₄Cl.