Gold-Catalyzed Oxidative Arylations of 3‑Butyn-1-ols and 2‑Propyn-1-ols with Nitrones to Yield Distinct Fused Indoles Bearing a Heterocyclic Ring

The catalytic formation of various fused indoles from the nitrone oxidations of 1-substituted n-yn-1-ols (n = 2, 3) is described. For 3-butyn-1-ols, the oxidations yield tetrahydropyrano­[4,3-b]­indoles, whereas 2-propynols deliver tetrahydro-[1,2]­oxazino­[5,4-b]­indoles efficiently. When styryl nitrones were tested on 2-propyn-1-ols, dihydrooxazolo­[3,4-a]­indoles were produced efficiently. We postulate that the formation of these fused indoles arises from a common mechanism, involving a [3,3]-sigmatropic shift of an initial alkenyl gold intermediate to furnish an oxoarylation before preceding to these fused indoles.