Synthesis of pyrroloindolines through formal [3 + 2]-cycloaddition of indoles with chiral N-2-acetamidoacrylyl oxazolidinones.

• Chiral acetamide oxazolidinones produced. • Reactions with indoles gave pyrroloindoline products. • This structure is found in many natural products. • Numerous indoles gave up to 91% yield with high selectivity. 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. [ABSTRACT FROM AUTHOR]