Raju Singha

KOtBu mediated efficient approach for the synthesis of fused heterocycles via intramolecular O-/N-arylations

A novel and efficient methodology for the synthesis of 6H-benzo[c]chromenes, 6H-benzo[c]chromen-6-ones, carbazoles, dibenzofurans, dibenzooxepins has been developed. The reaction goes through intramolecular O-/N-arylations with sp2C–Br bonds via typical SNAr pathway in presence of potassium-tert-butoxide base.

Pd-free Sonogashira coupling: one pot synthesis of phthalide via domino Sonogashira coupling and 5-exo-dig cyclization

Phthalides have been synthesized exclusively in one pot via Pd-free Sonogashira coupling. A Cu-catalyzed domino Sonogashira coupling and 5-exo-dig cyclization between suitable substituted ortho-bromobenzoic acids and terminal alkynes afforded phthalides in good yields under mild reaction conditions.

Highly stereo-selective synthesis of (Z)-2,3-diiodo-1,4-diarylbut-2-ene-1,4-diones via oxidative iodination of 1,4-diarylbuta-1,3-diynes

A novel and highly stereo and regioselective oxidative iodination of 1,4-diarylbuta-1,3-diynes promoted by N-iodosuccinamide results in (Z)-2,3-diiodo-1,4-diarylbut-2-ene-1,4-diones. In the case of NBS, the stereo-selectivity is moderate while NIS gives exclusively Z product. A plausible mechanism for the formation of both E and Z products is also proposed.

Copper catalyzed room temperature lactonization of aromatic C–H bond: a novel and efficient approach for the synthesis of dibenzopyranones

We have developed a novel and efficient methodology for the intramolecular aryl C–H oxidative lactonization of 2-arylbenzaldehyde using a low-cost CuCl catalyst and TBHP as the oxidant at room temperature. We applied the methodology to the synthesis of a series of dibenzopyranones.

Synthesis of α, β and γ-carbolines via Pd-mediated Csp2-H/N–H activation

An efficient method for the synthesis of halo-carbolines has been developed via Pd-catalysed formation of C–N bonds through Csp2-H/N–H activation of 4-methyl-N-[2-(pyridine-3-yl)phenyl] benzenesulfonamide derivatives. Pd(OAc)2 in the presence of Cu(OAc)2 as oxidant afforded halo-carbolines in good to excellent yields with tolerance to a variety of substituents.

Transition metal free synthesis of 2,4,6-trisubstituted pyrimidines via Cope-type hydroamination of 1,4-diarylbuta-1,3-diynes

We have developed an efficient and transition metal free methodology for the synthesis of 2,4,6-trisubstituted pyrimidines by the Cope-type hydroamination reaction of 1,4-diarylbuta-1,3-diynes with amidines in DMSO solvent.

Palladium catalyzed one-pot synthesis of 2-(pyridin-4-yl) quinolines via a multicomponent unprecedented reaction of pyridine-4-carbaldehyde, 2-iodoaniline and triethylamine

Palladium catalyzed synthesis of 2-(pyridin-4-yl) quinolines with an unprecedented participation of Et3N in moderate to high yields was achieved in a novel multicomponent one-pot cyclization reaction of readily available pyridine-4-carbaldehyde, 2-iodoaniline and triethylamine in refluxing toluene.

Pd-catalyzed intramolecular sequential Heck cyclization and oxidation reactions: a facile pathway for the synthesis of substituted cycloheptenone evaluated using computational studies

A simple and convenient method for the construction of substituted cycloheptenones from 1-bromoocta-1,7-diene-3-ols has been developed. The reaction involves Pd(0)-catalyzed intramolecular 7-exo-trig cyclization followed by Pd(II)-catalyzed oxidation of cyclic alcohol. The course of the reaction pathway has been evaluated using DFT calculations.

Synthesis of 4,5,6-trisubstituted-1,3-dihydroisobenzofurans by virtue of palladium-catalyzed domino carbopalladation of bromoenynes and internal alkynes

An efficient hetero-annulation protocol has been developed for the construction of 4,5,6-trisubstituted-1,3-dihydroisobenzofurans via palladium-catalyzed domino carbopalladation of bromoenynes and internal alkynes. The reaction followed domino intramolecular Heck cyclization (5-exo-dig) and termination of the resulting diene with an internal alkyne to give highly substituted isobenzofurans in moderate to good yields.

Synthesis of 1,3-dibromo-2-aryl-1H-indenes via NBS mediated unusual bromination of 2-alkynylbenzaldoximes

We have investigated a very interesting side-pathway leading to 1,3-dibromo-2-aryl-1H-indenes as opposed to isoquinoline N-oxides during the NBS mediated synthesis of isoquinoline N-oxide from 2-alkynylbenzaldoximes.