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Synthesis of pyrroloindolines through formal [3 + 2]-cycloaddition of indoles with chiral N-2-acetamidoacrylyl oxazolidinones
- Isaac T. Smith, Jared B. Neeley, Tanner D. Brinley, Peter R. Fullmer, Merritt B. Andrus
- Tetrahedron letters 2020 v.61 no.23 pp. 151947
- Lewis acids, catalysts, chemical structure, chlorides, cycloaddition reactions, enamines, indoles, methylene chloride, oxazolidinones, protonation, tautomerization, tin
- Chiral N-2-acetamidoacrylyl oxazolidinones were produced and reacted with indoles under Lewis acid conditions to generate hexahydropyrrolo[2,3-b]indole products in a formal [3 + 2] cycloaddition process. Optimal conditions included the use of tin(IV) chloride in methylene chloride at 0 °C. Pyrroloindoline products were obtained from various indoles with shorter reaction times (12 hr) up to 91% yield with high, >20:1 exo selectivity. A mechanism involving reversible conjugate addition followed by an enamine lone-pair-iminium capture, tautomerization, and tin-enolate protonation accounts for the selectivity. The method enables selective applications to pyrroloindoline targets and further refinement with chiral catalysts.