Synthesis of 1-pyrroline derivatives via cyclization of terminal alkynes with 2-azaallyls.

An efficient transition-metal-free cyclization reaction to prepare 1-pyrroline derivatives bearing various functional groups is described. In this method, a simple combination of a base and a solvent allows the cyclization reaction of terminal alkynes and 2-azaallyls to be carried out efficiently under mild and metal-free conditions. This cyclization reaction will provide an efficient method for the synthesis of medicinally relevant polysubstituted and multifunctionalized pyrrolines.

Multicomponent Cascade Reaction by Metal-Free Aerobic Oxidation for Synthesis of Highly Functionalized 2-Amino-4-coumarinyl-5-arylpyrroles.

A novel approach has been constructed for the synthesis of two types of 2-amino-4-coumarinyl-5-arylpyrroles (ACAPs, 5 and 6) through a cascade reaction and a metal-free catalyzed aerobic oxidation reaction of arylglyoxal monohydrates 1, 1,1-enediamines (EDAMs) 2 and 3, and 4-hydroxy-2H-chromen-2-ones 4 via multicomponent reactions to produce the target compounds with good to excellent yields. Specifically, hydroxyl-substituted 2-amino-4-coumarinyl-5-arylpyrroles, that is, 2-amino-4-coumarinyl-5-aryl-6-hydroxylpyrroles (ACAHPs) 6, were obtained by metal-free aerobic oxidation in 1,4-dioxane at simple reflux for approximately 10 h. As a result, ACAHPs 6 have been produced without metal catalysts or traditional oxidizing agents. This method represents a route to obtain the novel ACAPs in an environmentally friendly, concise, rapid, and practical manner with potential biological activity of the product.

Super-Electron-Donor 2-Azaallyl Anions Enable Construction of Isoquinolines.

Herein is introduced the application of "super-electron-donor"(SED) 2-azaallyl anions in a tandem reduction/radical cyclization/radical coupling/aromatization protocol that enables the rapid construction of isoquinolines. The value of this transition-metal-free method is highlighted by the wide range of isoquinoline ethyl amines prepared with good functional group tolerance and yields. An operationally simple gram scale synthesis is also conducted, confirming the scalability.

Transition-metal-free C(sp3)-H/C(sp3)-H dehydrogenative coupling of saturated heterocycles with N-benzyl imines.

A unique C(sp3)-H/C(sp3)-H dehydrocoupling of N-benzylimines with saturated heterocycles is described. Using super electron donor (SED) 2-azaallyl anions and aryl iodides as electron acceptors, single-electron-transfer (SET) generates an aryl radical. Hydrogen atom transfer (HAT) from saturated heterocycles or toluenes to the aryl radical generates alkyl radicals or benzylic radicals, respectively. The newly formed alkyl radicals and benzylic radicals couple with the 2-azaallyl radicals with formation of new C-C bonds. Experimental evidence supports the key hydrogen-abstraction by the aryl radical, which determines the chemoselectivity of the radical-radical coupling reaction. It is noteworthy that this procedure avoids the use of traditional strong oxidants and transition metals.

Three-Component Cascade Reaction of 1,1-Enediamines, N,N-Dimethylformamide Dimethyl Acetal, and 1,3-Dicarbonyl Compounds: Selective Synthesis of Diverse 2-Aminopyridine Derivatives.

A novel approach has been developed for the synthesis of three kinds of highly functionalized 2-aminopyridine derivatives (APDs) through a three-component reaction of 1,1-enediamines (EDAMs) 1, N,N-dimethylformamide dimethyl acetal (DMF-DMA) 2, and 1,3-dicarbonyl compounds 3-5 via a base-promoted cascade reaction, producing the desired products in good to excellent yields. This method represents a route to obtain a novel class of APDs in a concise, rapid, and practical manner. This approach is particularly attractive because of the following features: low cost, mild temperature, atom economy, high yields, and potential biological activity of the product.

Diastereoselective Synthesis of Morphan Derivatives by Michael and Hetero-Michael Addition of 1,1-Enediamines to Quinone Monoketals.

A general and concise method was developed for the synthesis of highly functionalized morphans 3-4 by the Michael and hetero-Michael addition reaction of different types of quinone monoketals 1 and 1,1-enediamines 2 in ethanol or 1,4-dioxane at reflux. This method is suitable for the efficient parallel syntheses of N-containing heterocycles. A library of highly functional morphan derivatives was easily constructed using the Michael/hetero-Michael reaction.