Synthesis of fused chromenes by indium(III)-catalyzed cascade hydroarylation/cycloisomerization reactions of polyyne-type aryl propargyl ethers.

Fused 2H-chromenes are prepared by the cascade hydroarylation/cycloisomerization reactions of polyyne-type aryl propargyl ethers using indium(III) catalysis. The transformation proceeds with 6-endo-dig regioselectivity using InBr₃ (5 mol%). The method can be extended to triynes allowing the formation of three bonds in one pot. Indium(III) also catalyzes the hydroamination/hydroarylation cascade reaction of o-aryldiynyl anilines to form fused carbazoles.