A simple and elegant strategy for the synthesis of furo[3,2-c]coumarin derivatives has been developed via a one-pot, [3+2] annulation of β-nitroalkenes with 4-hydroxycoumarins. This reaction involves the formation of two new bonds—one C–C and one C–O—and yields the desired fused heterocycle in a single step in presence of DABCO as the catalyst, and elemental sulfur as the oxidant. The transformation proceeds through a Michael addition/intramolecular cyclization/aromatization cascade, affording the desired products in moderate to good yields. The synthesized compounds exhibit fluorescence and their photophysical properties—including absorption, emission, and solvatochromism—were investigated.

Abstract

In this study, we report a simple and elegant method for the preparation of furo[3,2-c]coumarins from the one-pot, [3+2] annulations of β-nitroalkenes with 4-hydroxycoumarins in the presence of sulfur and DABCO as the catalyst. This method utilized readily available starting materials, thereby avoiding the use of prefunctionalized starting materials, and was performed under metal-free conditions thus, making it an alternate approach for the synthesis of furo[3,2-c]coumarin derivatives. The reaction proceeds via a Michael addition/intra-molecular cyclization/aromatization cascade to afford the desired product in moderate-to-good yields. As the compounds exhibit fluorescence under UV light, photophysical properties like absorption, emission of selected compounds, and solvatochromism were measured. Moreover, these compounds have potential pharmacological applications and can be employed as functional material, gram-scale synthesis of desired fused-heterocycles was demonstrated.