Rhodium(III)-and cobalt(III)-catalyzed C À Ha ctivation of indoles and coupling with 1,6-enynes is discussed. Under rhodium(III) catalysis,the alkyne insertion follows 2,1regioselectivity with asubsequent type-I intramolecular Diels-Alder reaction (IMDA) to afford[ 6,5]-fused cycles.W hen catalyzedb yt he cobalt(III) congener,1 ,2-insertion of the alkyne is preferred, and followed by arare type-II IMDA, thus leading to bridged [3,3,1]-cycles.T his selectivity of the alkyne insertion was mainly tuned by the steric sensitivity of the catalyst.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Scheme 6. Cobalt-catalyzed bridged cycle synthesis. Reactions were carried out using 1 (0.2 mmol), 2 (0.24 mmol), [Cp*Co(CO)I 2 ] (5 mol %), AgSbF 6 (10 mol %), and HOPiv (1 equiv) in TFE (2.0 mL) at 25 8 8Cfor 24 hunder N 2 .Yield is that of isolated product. ForX-ray structure thermal ellipsoids shown at 30 %probability. [17] Scheme 7. Mechanistic studies.
Angewandte ChemieCommunications 8165