Access to indoles via Diels-Alder reactions of 3-vinylpyrroles

Noland, W. E.; Lanzatella, N. P. J. Heterocycl. Chem. 2009, 46, 1285.

N-p-Toluenesulfonyl-3-vinylpyrrole underwent endo-addition [4 þ 2] cycloaddition reactions with maleimides and benzoquinones, followed by isomerization to give tetrahydroindoles in good yields. Dehydrogenation with activated MnO2 in refluxing toluene gave the corresponding indoles in fair to good yields. Detosylation via saponification or with magnesium in refluxing methanol gave the N-H indoles in moderate to good yields. This method for formation of indoles is both convergent and versatile and uses starting materials that are conveniently prepared.