Ph3PAuNTf2 as a Superior Catalyst for the Selective Synthesis of 2H-Chromenes: Application to the Concise Synthesis of Benzopyran Natural Products

Ph3PAuNTf2 (approximate to 1 mol-%) catalyzes the selective cycloisomerization of substituted aryl propargyl ethers into 2H-chromenes in excellent yields. Benzofuran byproducts are formed only in the case of electron-deficient arenes, in up to 7% relative yield. The Ph3PAuNTf2-catalyzed cyclization of aryl propargyl ethers was applied as a key step to the concise synthesis of the naturally occurring benzopyrans seselin, xanthyletin, precocenes I and II, 8-(3',3'-dimethylallyl)wenteria chromene, and 2,2-dimethyl-8-prenylchromene-6-propenoic acid.