Thorpe-Ingold effect in copper(II)-catalyzed formal hydroalkoxylation-hydroarylation reaction of alkynols with indoles

The use of Cu(OTf)(2) as a catalyst for tandem hydroalkoxylation-hydroarylation reaction of alkynes tethered with hydroxyl group is reported. The reaction proceeds at 60 degrees C or even at room temperature with 5 mol% catalyst loading and produces C-3-substituted indoles in good to high yields. The method was shown to be applicable to a broad range of indoles, containing electron-withdrawing and electron-donating substituents, and alkynol substrates bearing sterically demanding substituents in the tether. Interestingly, it was found that Thorpe-Ingold effect is operating for this cyclization reaction. Easy availability and low cost of Cu(OTf)(2) make this method attractive and amenable for large-scale synthesis compared to known literature methods. (C) 2009 Published by Elsevier Ltd