Microwave induced synthesis of a new class of pyrano isoxazoline and isoxazole annulated chromones - An intramolecular nitrile oxide cycloaddition with tethered olefins and alkynes

Abstract

A variety of new highly substituted 6-6-6-5-membered tetracyclic pyrano isoxazoline/isoxazole annulated chromone derivatives have been synthesized via eco-friendly microwave assisted/ceric ammonium nitrate (CAN) as an oxidant, intramolecular 1,3-dipolar cycloaddition with in situ generated nitrile oxides from aldoximes of alkene/alkyne tethered chromones. This protocol is practically simple and efficient to construct diverse range of substituted pyrano isoxazoline/isoxazole annulated chromone derivatives and gave higher yields of products in microwave irradiation compared to conventional heating. The structures of all the synthesized compounds were established by IR, NMR and MASS spectral analysis.