Subhendu Bhowmik

Synthesis of 3H-Pyrazolo[3,4-c]isoquinolines and Thieno[3,2-c]isoquinolines via Cascade Imination/Intramolecular Decarboxylative Coupling

A general approach for the synthesis of 3H-pyrazolo[3,4-c]isoquinolines and thieno[3,2-c]isoquinolines is described involving the implementation of a cascade imination/intramolecular decarboxylative coupling between potassium 2-amino(hetero)benzoates and 2-haloarylaldehydes. The reactions of pyrazole-based substrates require a Pd-Cu bimetallic system for superior yields whereas the thienyl-based substrates afford the products in excellent yields with a Pd-catalyst only.

Substituent‐Guided Switch between CH Activation and Decarboxylative Cross‐Coupling during Palladium/Copper‐Catalyzed Cascade Reactions of 2‐Aminobenzoates with 2‐Haloarylaldehydes

Substituent-Guided Switch between C H Activation and Decarboxylative Cross-Coupling during Palladium/ Copper-Catalyzed Cascade Reactions of 2-Aminobenzoates with 2-HaloACHTUNGTRENNUNGarylaldehydes Cascade switch : Phenanthridines, pyrazole ACHTUNGTRENNUNG[4,3-c]quinolines and isocryptolepine were prepared in one step from the Pd/Cu-catalyzed reaction between potassium 2-aminobenzoates and 2-haloarylaldehydes (see scheme). Although the reactions of 2-aminobenzoates proceeded via a cascade imination/C H functionalization, the reactions of 6-nitro-2-aminobenzoates ensued via a tandem imination/decarboxylative cross-coupling.

An Efficient Combinatorial Synthesis of Allocolchicine Analogues via a Triple Cascade Reaction and their Evaluation as Inhibitors of Insulin Aggregation

A controlled cascade: A divergent, diastereoselective and efficient one-pot synthesis of allocolchicinoids via a cascade Suzuki-Michael addition-Carbocyclization sequence is described. The utility of the compounds as possible inhibitors of insulin aggregation is also presented.

Synthesis of 4-substituted imino-4H-benzo(d)(1,3) thiazin-2-amines via palladium-catalysed isocyanide insertion in 2-bromophenylthioureas†‡

The palladium-catalysed isocyanide insertion in 2-bromophenylthioureas results in the formation of 4-substituted imino-4H-benzo[d][1,3]thiazin-2-amines via C–S cross coupling reaction of the intermediate imidoylpalladium species. The investigations into the substrate scope revealed that whereas reactions of cyclohexyl isocyanide were successful with aromatic as well as aliphatic thioureas, reactions of all other isocyanides (except ethyl 2-isocyanoacetate) were successful with aromatic thioureas only.

Microwave-assisted one-pot synthesis of 2-aryl-5,6-dihydro-4H-1,3-thiazines via reaction between Lawesson’s reagent and allyl arylamides derived from Morita–Baylis–Hillman acetates

A one-pot synthesis of 2-aryl-5,6-dihydro-4H-1,3-thiazines from the allyl arylamides afforded from the Morita–Baylis–Hillman acetates of acrylates has been developed. The protocol comprises of Lawesson’s reagent-mediated transformation of allyl arylamide to thioamide followed by tandem intramolecular sulfa-Michael reaction under microwave condition to afford the products as a mixture of syn and anti isomers. Based on a plausible mechanism syn and anti-isomers are proposed as the kinetic and thermodynamic products, respectively. Further it has been experimentally demonstrated that the syn isomer is transformed to the anti isomer via prolonged heating.

A novel stereoselective one-pot synthesis of 2-susbstituted amino-5,6-dihydro-4H-1,3-thiazines via primary allylamines afforded from Morita–Baylis–Hillman acetates

A new stereoselective synthesis of 2-susbstituted amino-5,6-dihydro 4H-1,3-thiazines using primary allylamines obtained from the Morita–Baylis–Hillman (MBH) acetates is described. The primary allylamines react with aryl isothiocyanates to afford the title compounds via sequential thiourea formation and intramolecular sulfa-Michael reaction in a one-pot process under two different experimental conditions. Two steps during the reactions between the allylamines derived from the MBH adducts of benzaldehyde or electron-donating group bearing substituted benzaldehydes and aryl isothiocyanates proceed in a cascade sequence to directly afford the anti-isomer of the title compounds. In contrast reactions between the allylamines generated from the MBH adducts of electron-withdrawing group containing substituted benzaldehydes and aryl isothiocyanate result in allyl thioureas which undergo Lewis acid-mediated intramolecular sulfa-Michael cyclization to afford syn or anti-products depending on the placement of the substitution on the phenyl ring. A plausible mechanism is proposed to explain the observed stereoselectivity amongst the prepared 1,3-thiazines.