Dipak Kalita

Pd/C-Mediated synthesis of indoles in water

Summary We describe the utility of a Pd/C-Cu mediated method in the synthesis of 2,5-disubstituted indoles in water via a coupling-cyclization strategy. Further application of this methodology has been demonstrated in the preparation of a target indole derivative via a 7-step process the key step being the Pd/C-mediated coupling reaction.

A catalyst-free rapid, practical and general synthesis of 2-substituted quinazolin-4(3H)-ones leading to luotonin B and E, bouchardatine and 8-norrutaecarpine

A remarkably rapid but microwave/ultrasound/catalyst-free method has been developed for the construction of a quinazolin-4(3H)-one ring using formamide as an efficient ammonia precursor and PEG-400 as an effective solvent. The methodology afforded various 2-substituted quinazolin-4(3H)-one derivatives in good yield via a three-component reaction of isatoic anhydride, aldehydes and formamide in air. This single methodology was extended successfully to the synthesis of several alkaloids e.g. leutonin B and E, bouchardatine and 8-norrutaecarpine.

Catalysis by FeF3 in water: a green synthesis of 2-substituted 1,3-benzazoles and 1,2-disubstituted benzimidazoles

FeF3 in water facilitated the reaction of 1,2-phenylenediamine and 2-aminothiophenol with 1 equivalent of an alkyl- or aryl-aldehyde leading to 1,3-benzazoles in open air. The process afforded 1,2-disubstituted benzimidazoles when 1,2-phenylenediamine was reacted with 2 equivalents of aryl aldehyde. The methodology is operationally simple, free from the use of hazardous organic solvents and chemoselective. The products were isolated by simple filtration and the catalyst can be recovered and recycled.

Palladium-catalyzed C–N and C–O bond formation of N-substituted 4-bromo-7-azaindoles with amides, amines, amino acid esters and phenols

Summary Simple and efficient procedures for palladium-catalyzed cross-coupling reactions of N-substituted 4-bromo-7-azaindole (1H-pyrrole[2,3-b]pyridine), with amides, amines, amino acid esters and phenols through C–N and C–O bond formation have been developed. The C–N cross-coupling reaction of amides, amines and amino acid esters takes place rapidly by using the combination of Xantphos, Cs2CO3, dioxane and palladium catalyst precursors Pd(OAc)2/Pd2(dba)3. The combination of Pd(OAc)2, Xantphos, K2CO3 and dioxane was found to be crucial for the C–O cross-coupling reaction. This is the first report on coupling of amides, amino acid esters and phenols with N-protected 4-bromo-7-azaindole derivatives.

Indion Ina 225H resin as a novel, selective, recyclable, eco-benign heterogeneous catalyst for the synthesis of bis(indolyl)methanes

Abstract Indion Ina 225H, is a heterogeneous, selective, recyclable, and eco-benign catalyst for liquid phase electrophilic substitution reactions of indoles with aldehydes to afford the corresponding bis(indolyl)methanes in excellent yields in short reaction time. The versatility of this method has been proved with a wide range of aliphatic and aromatic aldehydes with various stereo-electronic factors. This method shows much better selectivity between aldehydes and ketones. The methodology is well demonstrated toward the synthesis of biologically active bis(indolyl)methanes viz, vibrioindole, 4-(di(1H-indol-3-yl)methyl)benzene-1,2-diol and streptindole. The catalyst can be recovered and reused for several runs without loss of activity.

Sulfonic acid–functionalized Wang resin (Wang-OSO3H) as polymeric acidic catalyst for the ecofriendly multicomponent synthesis of polyhydroquinolines via Hantzsch condensation

ABSTRACT An efficient and green approach has been developed for the synthesis of polyhydroquinoline derivatives via Hantzsch condensation reaction directly from corresponding substituted aromatic and aliphatic aldehydes, β-keto compounds, active methylene compounds, and ammonium chloride using recyclable polymer-supported sulfonic acid catalyst under aqueous conditions. Environmental acceptability, operational simplicity, low cost, excellent functional group compatibility, and high yields are the important features of this protocol. GRAPHICAL ABSTRACT