One-pot synthesis of 6,11-dihydro-5H-indolizino[8,7-b]indoles via sequential formation of β-enamino ester, Michael addition and Pictet–Spengler reactions

Abstract

β-Enamino esters generated from addition of tryptamines to alkyl propiolates reacted with 3-phenacylideneoxindoles in the presence of anhydrous ZnCl₂ to give functionalized 2-pyrrolo-3′-yloxindoles in satisfactory yields, which can be further converted to the corresponding 6,11-dihydro-5H-indolizino[8,7-b]indoles in good yields through a CF₃SO₃H catalyzed Pictet–Spengler cyclization process. Under similar conditions, when arylamines were used to replace tryptamine, the one-pot domino reaction afforded the functionalized 2-pyrrolo-3′-yloxindoles.