Cycloaddition of Benzyne with Alkoxy-Substituted Pyrroline-N-oxides­: Unexpected Rearrangement to an N-Phenylpyrrole

Abstract

Abstract Reaction of enantiopure 3,4-dialkoxy-pyrroline N-oxides with benzyne affords the expected tetrahydrobenzo[d]pyrrolo[1,2-b]isoxazoles along with an unexpected 2,3-disubstitued-N-phenyl-pyrrole derived from an unprecedented rearrangement of the adduct of nitrone with two molecules of benzyne. A mechanism for the unusual rearrangement is proposed. The benzo[d]isoxazolidine derivatives are conveniently converted into 2-(2-hydroxyphenyl)-3,4-dialkoxypyrrolidines by reductive opening of the N–O bond.

Keywords

• arynes
• fused-ring systems
• heterocycles
• pyrroles
• rearrangement
• 1,3-dipolar cycloaddition
• nitrones