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In this study, we report the synthesis of several novel dihydroisoxazole-, tetrahydroisoxazole- and dihydropyrazole-fused pyrido[2,3-b]quinolines, α-carbolines, and pyrido[2,3-c]coumarins, respectively, from simple precursors and by exploring intramolecular 1,3-dipolar cycloaddition reactions involving nitrile oxides, nitrones, and nitrile imines as 1,3-dipoles.

A simple and efficient method for the synthesis of highly functionalized furo[3,2- c ]coumarins was developed. The reaction occurred via initial formation of biscoumarins from the reaction of 4-hydroxycoumarins and aldehydes/aryl methyl ketones in the presence of molecular iodine in DMSO followed by lactone ring opening, cyclization and oxidative aromatization process. The reaction conditions were moderate, work-up procedure was simple and products were obtained in high yield. [ABSTRACT FROM AUTHOR]

Abstract: Some novel spiro substituted pyrido[2,3-c]coumarin derivatives were synthesized from 4-hydroxycoumarin by exploring ‘tertiary amino effect’ reaction strategy. [Copyright &y& Elsevier]

The transformation follows an initial iodine-catalyzed reaction of 4-hydroxycoumarins with carbonyl compounds to biscoumarins followed by lactone ring opening, cyclization, and oxidative aromatization. [ABSTRACT FROM AUTHOR]

A four-step sequence is presented for the conversion of 4-hydroxycoumarin into spiro substituted pyridocoumarin (VIII). [ABSTRACT FROM AUTHOR]