Development of catalytic one-pot approaches to heterocycle fused coumarins, 2-oxindoles and carbocyclic scaffolds

Abstract

The main objective of the present thesis work is to develop one-pot catalytic approaches for the efficient synthesis of interesting classes of fused coumarins based scaffolds, spirooxindoles and carbocyclic frameworks from simple raw materials. This chapter begins with the general introduction which describes the diverse applications of heterocycles fused to coumarins and 2-oxindole framework. It also includes a brief discussion of the reported protocols devised for the synthesis of aforesaid compounds. The second chapter demonstrates an efficient, solvent-free, environmentally benign, Cu(OTf)2-catalyzed and microwave-assisted synthesis of a fascinating class of angularly fused chromenopyridinones via a one-pot [3+3] annulation reaction of several aminocoumarins/cyclic β-enaminones with different kinds of γ-aryl/styryl/heteroaryl-substituted-β,γ-unsaturated α-ketoesters as Michael acceptors under open atmosphere. Moreover, this method also facilitates the stereoselective synthesis of trans-7,8-diaryl-8.9-dihydrochromeno[4,3-b]cyclopenta[e]pyridine-6,10-diones in an excellent diastereoselectivities (dr ≤ 99:1). The third chapter presents an efficient, organocatalytic, eco-friendly and stereoselective approach for the construction of medicinally promising spirooxindole-fused-dihydropyran scaffolds by performing a one-pot allylic alkylation/oxa-Michael reaction between a wide range of Morita-Baylis-Hillman (MBH) carbonates of isatins and several enolizable C-H activated cyclic carbonyl compounds as 1,3-binucleophiles namely pyrazolones, isoxazolones, 4-hydroxycoumarins, 4-hydroxy-6-methyl-α-pyrone, lawsone and dimedone in a biomass-derived 2-MeTHF as green solvent catalyzed by DABCO as a solid Lewis-base catalyst. The fourth chapter describes a L-proline catalyzed domino nitro-Michael/aldol reaction between several β-aryl-substituted-γ-nitroketones and a range of β-aryl-substituted acroleins for the synthesis of densely functionalized cyclohexanol derivatives having five contiguous chiral in good to high yields with high diastereoselectivities. Furthermore, one-pot conversion of cyclohexanols to a novel class of 2,3,4,6-tetrasubstituted phenols under metal-free conditions has also been highlighted. In the fifth chapter, a Lewis acid-catalyzed, microwave-assisted, solvent-free and one-pot approach has been established to access a new class of diversely substituted coumarin, dimedone and naphthoquinone-fused pyrroles via [3+2] annulation reaction of different kinds of carbo/heterocyclic enaminones with a bunch of α-aroyl/heteroaryl/acetylidene malonates, 3- aroylidene-2-oxindoles. Furthermore, the synthesized pyrrolocoumarinyl-2-oxindoles were subjected to C(sp3)-H hydroxylation to afford biologically exciting 3-hydroxy-3 pyrrolocoumarinyl-2-oxindoles bearing a tetra-substituted chiral carbon center in high yields under metal-free conditions. The last chapter of this thesis focuses on the conclusions and future outcomes of the developed protocols.