PIDA Mediated Synthesis of Benzopyranoisoxazoles via an Intramolecular Nitrile Oxide Cycloaddition (INOC): Application to the Synthesis 4H‐chromeno[4,3‐c]isoxazol‐4‐ones.

Abstract

Abstract Presented herein is an approach for the synthesis of highly substituted tricyclic benzopyranoisoxazoles from the corresponding aldoximes via an intramolecular nitrile oxide cycloaddition (INOC) reaction using a hypervalent iodine reagent (Diacetoxyiodo)benzene (PIDA/DIB/(PhI(OAc) 2 ) as the single inexpensive oxidizing agent. The key step involved in this reaction is a sequential intramolecular C−C and C−O bond formation. A variety of benzopyranoisoxazoles were constructed in moderate to high yields. In addition, some of the benzopyranoisoxazoles were converted to 4H‐chromeno[4,3‐c]isoxazol‐4‐ones via allylic oxidation using CrO 3 as an oxidant.