Switchable Synthesis of α- or β-Keto Naphthalenes via Gold-Catalyzed Divergent Cycloisomerization of 1,6-Diyn-3-ols and Its Application in the Total Synthesis of Justicidin B and Taiwanin C.

A switchable divergent gold catalysis is described that employs 1,6-diyn-3-ols as a common starting material for the regioselective synthesis of β-keto and α-keto naphthalenes. Under Au(I) catalysis, the α-keto naphthalenes are obtained regioselectively. In contrast, the β-keto naphthalenes are obtained as the major products in the presence of a Au(III) catalyst. The mechanism involves an initial gold-catalyzed 6-endo-dig oxacyclization, subsequent C-O bond scission and divergent cycloisomerization, ultimately leading to either 1,3-acyl transposition or retention of the acyl group on the naphthalene skeleton. The synthetic utility is demonstrated in the concise total synthesis of justicidin B and taiwanin C.