Bronsted Acid-Catalyzed Regioselective Carboxamidation of 2-Indolylmethanols with Isonitriles.

A regioselective direct carboxamidation reaction of 2-indolylmethanols with readily available isocyanoesters/isocyanides has been reported in this work. The reaction was catalyzed by Bronsted acid such as p-TsOH to deliver the benzylic regioselective amides in 67-86% yield under mild conditions. The developed methodology provides alternative access to traditional metal-free carboxamidation via C-C and C-O bond formation with high atom economy. Furthermore, the developed approach was diversified to synthesize chiral indole-2-carboxamide derivatives with a moderate enantiomeric excess (61-73% ee) using an (R)-chiral phosphoric acid.

Recent approaches to the synthesis of tetrahydrocarbazoles.

The tetrahydrocarbazole (THC) motif is ubiquitous in natural products and biologically active compounds. THCs can serve as favorable synthetic intermediates or precursors en-route to desired complex natural products. Despite a considerable number of strategies for the synthesis of THCs that have emerged in the last two decades, only a handful of reviews have been published on the subject. Herein, we have summarized synthetic methodologies published in the last ten years for the benefit of organic chemists. The review focuses on non-enantioselective syntheses of THCs, and encompasses ring opening reactions of donor-acceptor cyclopropanes, metal-catalyzed C-C/C-N bond formation, cycloaddition, conjugate addition, and miscellaneous reactions employed for accessing the THC framework.

Facile access to functionalized indenes and fused quinolines by regioselective 5-enolexo-dig Michael addition and cyclization reactions.

Herein we report a facile approach to synthesise multi-substituted indenes and cyclopenta[b]quinolines under mild conditions. The reaction proceeds via Michael addition between commercially available cyanoacetate/malonic esters and α,ß-unsaturated ketones. The synthetic methodology involves enolate mediated regio- and stereoselective intramolecular 5-enolexo-dig cyclization promoted by a catalytic base. The products stereoselectively form cis-isomers for indenes and trans-isomers for cyclopenta[b]quinolines, albeit with the presence of steric hindrance at a quaternary carbon substituted by active methylene compounds. The reaction pathway was investigated by isolating the reaction intermediate. This synthetic transformation was achieved with various aromatic and heteroaromatic Michael acceptors and the desired products were obtained in high to excellent yields. The reaction is scalable up to gram level with only 10 mol% of base.

Regioselective synthesis of functionalized dihydroisoquinolines from o-alkynylarylaldimines via the Reformatsky reaction.

A novel approach for the synthesis of functionalized 1,2-dihydroisoquinolines from o-alkynylarylaldimines via the Reformatsky reaction without the aid of an external Lewis acid has been described. The chemistry involves the dual role of the Reformatsky reagent which has been generated in situ in the reaction. We propose that one molecule of the Reformatsky reagent is being utilised for the activation of alkynes, whereas the second molecule acts as a nucleophile on the iminium carbon. This synthetic pathway has high functional group tolerance, and can be utilized on a gram scale. The proposed mechanistic pathway is well supported by the control experiments. The 1,2-dihydroisoquinoline derivatives showed up to 90% inhibition of the strand transfer activity of the HIV integrase enzyme.

Chemo-, regio-, and stereoselective Heck-Matsuda arylation of allylic alcohols under mild conditions.

Heck arylation with allylic alcohol is extremely challenging due to chemo-, regio-, and stereoselective scrambling. Here we report a mild protocol for the alcohol selective ß- and α-arylation of allylic and cinnamyl alcohols respectively with aryldiazonium salts. The steric and electronic parameters of the alkene play a prominent role in the regioselectivity.