New Diels–Alder reactions of 3-vinylindoles with an aryne: selective access to functionalized [a]anellated carbazoles

Abstract

New results for the reactions of donor- and acceptor-substituted 3-vinylindoles with aryne and structurally related 3,4-pyridyne are described. Aryne reacts in Diels–Alder reactions as a dienophile to give rise to a variety of [a]anellated carbazoles in a one-step procedure. Additionally, aryne is involved in an ene or conjugate addition reaction with the initially formed [4 + 2]cycloadduct. Reaction of methyl (E)-3-(N-methylindol-3-yl)propenoate 6 in the presence of air gives besides the expected Diels–Alder product a new benzoxepino[b]indole derivative 14. The Diels–Alder reactions of the 3-vinylindoles with in situ generated 3,4-pyridyne are difficult to control and no cycloadducts with the required purity could be isolated.