Oxidation Strategy for the Synthesis of Regioisomeric Spiroisobenzofuranopyrroles: Facile Entries to Spiro[isobenzofuran-1,2′-pyrrole] and Spiro[isobenzofuran-1,3′-pyrrole] Derivatives

Two practical and efficient approaches have been developed to synthesize two kinds of racemic spiroisobenzofuranopyrrole analogues as regioisomers. In the presence of sodium periodate, cis -indeno[1,2- b ]pyrrol-4(1 H )-ones were converted into spiro[isobenzofuran-1,2′-pyrrole] derivatives by a two-step process. In addition, oxidative reactions promoted by lead tetraacetate were demonstrated using cis -indeno[2,1- b ]pyrrol-8(1 H )-ones as substrates, affording spiro[isobenzofuran-1,3′-pyrrole] derivatives. The remarkable features of two approaches included mild and convenient reaction conditions, a broad substrate scope, and moderate to excellent yields. Possible mechanisms were proposed based on the comparison of the intermediates and products.