Soumen Biswas

Stereoselective synthesis of highly functionalized tetrahydrocarbazoles through a domino Michael–Henry reaction: an easy access to four contiguous chiral centers

For the first time, a very simple, efficient, mild, catalytic and one-step procedure for the synthesis of a series of densely functionalized 1-methoxycarbonyl-2-aryl-3-nitro-4-hydroxy-1,2,3,4-tetrahydro-9H-carbazole derivatives has been achieved via a domino Michael–Henry reaction of methyl 3-formyl-1H-indole-2-acetates with β-nitrostyrenes using DABCO as an organocatalyst. Furthermore, the high enantio-(≤92% ee) and diastereoselective (≤12 : 1 dr) synthesis of the title compounds has been achieved with excellent yields using 9-O-benzylcupreidine (10 mol%) as a catalyst.

Access to 4,6-Diarylpicolinates via a Domino Reaction of Cyclic Sulfamidate Imines with Morita-Baylis-Hillman Acetates of Nitroolefins/Nitrodienes.

An interesting domino reaction of 5-membered cyclic sulfamidate imines with a variety of Morita-Baylis-Hillman acetates of nitroolefins/nitrodienes in the presence of DABCO as an organic base at 55 °C is reported for the first time. This new synthetic strategy provides a series of pharmacologically interesting 4,6-diarylpicolinates in high to excellent yields and allows several compatible functionalities on aryl rings. Moreover, the biologically interesting imidazo[1,2-a]pyridine (alpidem derivative) has been prepared in high chemical yield through a unique procedure.

Organocatalysed Michael addition on arylmethylidenemalonates involving 4-(2-nitrophenyl)acetoacetate: diversity-oriented access to 8,9-dihydropyrido[1,2-a]indol-6(7H)-one and salicylate scaffolds

Excellent diastereoselective (≤96 : 4) preparation of new functionalized 7,8,9-trisubstituted-8,9-dihydropyrido[1,2-a]indol-6(7H)-ones has been achieved in 61–81% yields through a one-pot reductive cycloaromatization–lactamization sequence reaction of Michael adducts using Zn/NH4Cl as a reducing agent. In addition, one-pot synthesis of sterically demanding hexa-substituted salicylate derivatives has been successfully realized via a tandem reaction of alkylidene malonates or aldehydes with 2-nitrophenyl-β-keto ester under aerobic conditions using DBU as an organocatalyst.

Metal- and Solvent-Free Approach to Diversely Substituted Picolinates via Domino Reaction of Cyclic Sulfamidate Imines with β,γ-Unsaturated α-Ketocarbonyls

An efficient, solvent-free, and eco-friendly domino reaction of 5/6-membered cyclic sulfamidate imines with a variety of β,γ-unsaturated α-ketocarbonyls in neat conditions under MW irradiation promoted by DABCO as a solid organobase has been developed for the rapid construction of a novel class of densely functionalized picolinates. This interesting metal-solvent-free tactic allows a wide range of useful functionalities on the aryl rings and delivers good to excellent yields of the aforesaid aza-heterocycles within short time spans (20-40 min). A biologically promising imidazo[1,2-a]pyridine was successfully synthesized through our unique procedure.