Gold-Catalyzed Heteroannulation Route to Indolin-3-ones and Indoles

Significance

Based on the gold(I)-catalyzed intramolecular acetylenic Schmidt reaction (conversion of homopropargyl azides into pyrroles via 1,2-shift on an α-imino gold carbene: D. J. Gorin, N. R. Davis, F. D. Toste J. Am. Chem. Soc. 2005, 127, 11260), Gagosz and co-workers explored the trapping of the α-imino gold carbene 2 derived from 1 with a nucleophile, for example allylic alcohols 4. Instead of the expected 2,3-disubstituted indole product 3, the indoline-3-one 5 was obtained, resulting from a Claisen rearrangement of the desired 2,3-disubstituted indole 3. [(IAd)AuNTf₂] (A) proved to be the best catalyst for this transformation. When performed with other alcohols unsuitable for the Claisen rearrangement, the reaction led to 3-alkoxyindoles 3 in moderate to good yields. When aromatic nucleophiles were used, 3-arylindoles 6 and 7 were obtained as the result of a Friedel-Crafts reaction. A mechanism was suggested without evidence.