Search

A trifluoroacetic acid promoted step-economical one-pot approach to the synthesis of furo-fused quinoxalines/ pyrazines by the reaction of 2,3-dichloroquinoxalines/pyrazines with alkynes is described. The reaction involves a selective insitu Sonogashira coupling step and a hydroxylation followed by a metal-free 5-endo-dig cyclization. Preliminary experiments show that trifluoroacetic acid acts as a source of oxygen for the oxyarylation step, and isotopic labeling studies support the proposal that the mechanistic pathway involves activation of the alkyne by the acidic medium. Various kinds of substituents are tolerated, which should prove valuable for structural and biological investigations. [ABSTRACT FROM AUTHOR]

A novel PdII-catalyzed approach for the direct synthesis of highly functionalized carbazoles from unprotected styrylindoles has been developed. The reaction features a variety of olefin substrates, which are readily switchable by subtle tuning of the reaction conditions. Investigations of the mechanism suggest that the C–H activation proceeds via enamine formation. [ABSTRACT FROM AUTHOR]

An efficient copper-catalyzed tandem approach for the synthesis of 2-imino[1,3]benzothiazines by the reaction of easily accessible 2-aminoaryl acrylates with isothiocyanates via in situ thioamidation and concomitant chemoselective intramolecular thia-Michael addition is described. Intramolecular cyclization was selectively triggered by the nitrogen ‘ b ’ of the thiourea intermediate P . [ABSTRACT FROM AUTHOR]

Abstract: An efficient strategy for the synthesis of α,β-unsaturated enaminones by the nucleophilic addition of N-heterocycles such as indole and imidazoles onto electronically bias alkynones under mild reaction conditions is described. Key feature of this reaction is the chemoselective addition of N-heterocycles onto ynones without affecting the 1o amino groups (aromatic and aliphatic) of 5-aminoindole and tryptamine. The stereochemistry of the products was controlled by the tuning of reaction time. The mechanism of the reaction involves the Michael type addition of N-heterocycles on ynones via allene formation.Graphical Abstract: [ABSTRACT FROM AUTHOR]

An abstract of the article "On Water: Catalyst-Free Chemoselective Synthesis of Highly Functionalized Tetrahydroquinazolines from 2-Aminophenylacrylate" is presented.

An efficient approach for the silver-catalyzed regioselective tandem synthesis of highly functionalized 1,2-dihydrobenzo[1,6]naphthyridines 6a-z and 7a-e by the reaction of ortho-alkynylaldehydes 3a-n with amines 4a-d and ketones 5a-c/active methylene compounds 5d-g, under mild reaction conditions, is described. The scope of the developed chemistry was successfully extended for the direct synthesis of 1,2-dihydrobenzo[4,5]thieno[2,3-c]pyridines 8a-e, which is known as the sulfur analogue of β-carbolines. Naphthyridines 6a-z and thienopyridines 8a-e were obtained via dual activation concept using l-proline as organocatalyst; however, naphthyridines 7a-e were synthesized without using organocatalyst. The reaction shows selective N-C bond formation on the more electrophilic alkynyl carbon, resulting in the regioselective 6-endo-dig-cyclized products. Reactivity behavior of electron-deficient and electron-rich ortho-alkynylaldehydes in the synthesis of naphthyridines and thienopyridine by three-component reaction is supported by the control experiment. [ABSTRACT FROM AUTHOR]