Nonoxidovanadium(IV) Complex-Catalyzed Synthesis of 2-Amino-3-cyano-4-pyrans/4-chromenes, Biscoumarins, and Xanthenes under Green Conditions.

Reaction of [VO(acac)] (Hacac = acetylacetone) with a Mannich base, ,,','-tetrakis(2-hydroxy-3,5-di-butyl benzyl)-1,2-diaminoethane (HL, ) in a 1:1 molar ratio in MeOH, leads to the formation of the nonoxidovanadium(IV) complex [VL] (). Air stable complex has been characterized using various spectroscopic techniques, DFT calculations, and single-crystal X-ray studies. adopts distorted octahedral geometry where ligand coordinates through all coordination functionalities available. This complex has been used as a catalyst in the one-pot, three-component synthesis of 2-amino-3-cyano-4-pyrans using 1,3-dicarbonyls (1,3-cyclohexanedione, dimedone, barbituric acid, and 4-hydroxycoumarin), malononitrile, and various substituted aromatic aldehydes in equimolar amounts employing ethanol as a green solvent. The catalytic reaction revealed that the multicomponent synthesis of 4-pyrans and chromenes is greatly influenced by both types of 1,3-dicarbonyl compound employed and the nature of the substituent on the aromatic ring of the aldehyde. Synthesized catalyst has also been used in the synthesis of pharmacologically relevant oxygen-containing heterocycles, specifically, 1,8-dioxo-octahydro-1-xanthenes and biscoumarins. The possible mechanism for the synthesized one-pot, multicomponent product has been proposed by isolating intermediate(s) generated during synthesis.