Cu/TEMPO catalyzed dehydrogenative 1,3-dipolar cycloaddition in the synthesis of spirooxindoles as potential antidiabetic agents

Abstract

A series of spiro-[indoline-3,3'-pyrrolizin/pyrrolidin]-2-ones, 4, 5 and 6 were synthesized in a sequential manner from Cu-TEMPO catalyzed dehydrogenation of alkylated ketones, 1 followed by 1,3-dipolar cycloaddition of azomethine ylides via decarboxylative condensation of isatin, 2 and l-proline/sarcosine, 3 in high regioselectivities and yields. The detailed mechanistic studies were performed to identify the reaction intermediates, which revealed that the reaction proceeds via dehydrogenative cycloaddition. Additionally, the regio and stereochemistry of the synthesized derivatives were affirmed by 2D NMR spectroscopic studies. The synthesized derivatives were explored further with molecular docking, in vitro antioxidant, and anti-diabetic activities.

Fig. 1. Bioactive spirooxindole natural products.

Scheme 1. 1,3-Dipolar cycloaddition of α,β-unsaturated carbonyl compounds (previous work).

Scheme 2. Synthesis of spirooxindoles by sequential dehydrogenative 1,3-dipolar cycloaddition of alkylated ketones (this work).

Fig. 2. Plausible mechanism for the synthesis of spirooxindoles from keto-alkanes via Cu–TEMPO catalyzed dehydrogenation and 1,3-dipolar cycloaddition.