Indresh Kumar

Cycloaddition Reactions: A Controlled Approach for Carbon Nanotube Functionalization

Controlled functionalization of carbon nanotubes (CNTs) through the use of cycloaddition reactions is described. By employing various cycloaddition reactions, a wide range of molecules could be coupled onto CNTs without disruption of the structural integrity as well as with a statistical distribution of functional groups onto the surface of the CNTs. The cycloaddition reactions represent an effective and tailored approach for preparing CNT-based advanced hybrid materials that would be useful for a wide range of applications from nanobiotechnology to nanoelectronics.

An organocatalytic direct Mannich–cyclization cascade as [3+2] annulation: asymmetric synthesis of 2,3-substituted pyrrolidines

A new method for asymmetric synthesis of 2,3-substituted pyrrolidines from N-PMP aldimines and succinaldehyde via formal [3+2] cycloaddition is reported. This reaction involves proline catalyzed direct Mannich reaction and acid catalyzed reductive cyclization with high yields (up to 78%) and excellent enantioselectivities (up to >99%).

1,3-Carbon D–A strategy for [3 + 2] cycloadditions/annulations with imines: synthesis of functionalized pyrrolidines and related alkaloids

Cycloaddition/annulation reactions remain the most attractive methods for the synthesis of five membered heterocyclic ring systems. Among the three possible strategies for [3 + 2] cycloaddition, this review focuses on 1,3-carbon donor–acceptor (C3, D–A) cycloaddition/annulation reactions with imines to synthesize pyrrolidines. The formal [3 + 2] cycloaddition, which includes the in situ 1,3-carbon D–A precursor generation through metal catalysis, Lewis acid catalysis and organocatalysis approaches is highlighted. The scope and limitations of this strategy along with its applications in the synthesis of natural product alkaloids reported during the last decade are outlined.

Enantioselective Synthesis of N-PMP-1,2-dihydropyridines via Formal [4 + 2] Cycloaddition between Aqueous Glutaraldehyde and Imines.

A simple and highly practical one-pot formal [4 + 2] cycloaddition approach for the enantioselective synthesis of N-PMP-1,2-dihydropyridines (DHPs) is described. This chemistry involves an amino-catalytic direct Mannich reaction/cyclization followed by IBX-mediated chemo- and regioselective oxidation sequence between readily available aqueous glutaraldehyde and imines under very mild conditions. A series of N-PMP-1,2-DHPs have been prepared in high yields and excellent enantioselectivity. This method also gives access to both enantiomers of 1,2-DHPs in surplus amount by shifting the catalyst configuration.

Organocatalytic Mannich/cyclization/aromatization sequence: direct synthesis of substituted pyrrole-3-carboxaldehydes

A robust method for the synthesis of substituted pyrrole-3-carboxaldehydes from N-PMP aldimines and succinaldehyde is reported. This reaction involves an organocatalytic direct Mannich reaction, and an acid catalyzed cyclization and oxidative aromatization sequence with high yields (up to 82%).

Facile and Highly Selective Deprotection of tert‐Butyldimethyl Silyl Ethers using Sulfated SnO2 as a Solid Catalyst

Abstract Highly selective deprotection of tert‐butyldimethylsilyl ethers at room temperature has been described using sulfated SnO2 as an efficient solid catalyst.

Direct catalytic synthesis of densely substituted 3-formylpyrroles from imines and 1,4-ketoaldehydes

A sustainable method for the direct access to highly substituted 3-formylpyrroles from 1,4-ketoaldehydes and imine via formal [3 + 2] cycloaddition is reported. This reaction involves a one-pot amine catalyzed chemoselective Mannich-cyclization-aerobic oxidation sequence with good to high yields. Further application of the gram scale reaction as well as synthesis of fully substituted 3-formylpyrrole is also shown.

Enantioselective synthesis of 1,2,5,6-tetrahydropyridines (THPs) via proline-catalyzed direct Mannich-cyclization/domino oxidation–reduction sequence: application for medicinally important N-heterocycles

An enantioselective multi-component synthesis of 1,2,5,6-tetrahydropyridines (THPs) has been developed through a one-pot domino-process. This transformation proceeds through proline-catalyzed direct Mannich reaction-cyclization of glutaraldehyde with in situ generated imines, followed by site-selective oxidation–reduction sequence under mild conditions. Chiral 1,2,5,6-THPs are obtained in good to high yields (up to 80%) and with the excellent enantioselectivity (up to 98 : 2 er). The usefulness of this operationally simple method is also shown to synthesize other medicinally important nitrogen-heterocycles.

Microwave assisted aminocatalyzed [3 + 2] annulation between α-iminonitriles and succinaldehyde: synthesis of pyrrole-3-methanols and related polycyclic ring systems

A quick and highly efficient method for the synthesis of substituted pyrrole-3-methanols from α-iminonitriles and succinaldehyde under microwave irradiation is reported. This one-pot method involves aminocatalyzed direct Mannich reaction-cyclization-dehydrocyanation followed by NaBH4 reduction sequence in good yields (up to 75%). Further applications of this method are demonstrated through the rapid synthesis of polycyclic heterocycles such as pyrrolo-dihydrochromene and pyrrolo-dihydroquinoline compounds.

One-pot sequential multicomponent reaction between in situ generated aldimines and succinaldehyde: facile synthesis of substituted pyrrole-3-carbaldehydes and applications towards medicinally important fused heterocycles

An efficient sequential multi-component method for the synthesis of N-arylpyrrole-3-carbaldehydes has been developed. This reaction involved a proline-catalyzed direct Mannich reaction-cyclization sequence between succinaldehyde and in situ generated Ar/HetAr/indolyl-imines, followed by IBX-mediated oxidative aromatization in one-pot operation. The practical utility of this procedure is shown at gram-scale and the synthesis of diverse bioactive fused heterocyclic scaffolds such as pyrroloquinoline, pyrrolo-oxadiazole, dihydro pyrroloquinoline, and pyrrolo-phenanthridine.