Access to Indoles via Diels-Alder Reactions of 2-Vinylpyrroles with Maleimides

Noland, W. E.; Lanzatella, N. P.; Venkatraman, L.; Anderson, N. F.; Gullickson, G. C. J. Heterocycl. Chem. 2009, 46, 1154.

Variously substituted 2-vinylpyrroles underwent an endo-addition [4þ2] cycloaddition reaction with maleimides followed by a spontaneous highly diastereoselective (93–98% de) isomerization to give tetrahydroindoles in moderate to excellent yield. Treatment with activated MnO2 in refluxing toluene provided the corresponding indoles in moderate to good yield. This highly convergent methodology for formation of indoles is versatile and the starting materials are conveniently prepared.