Metal-free synthesis of 1H-indole-2-carbaldehydes by N-iodosuccinimide-mediated cyclization of 1-(2′-anilinyl)prop-2-yn-1-ols in water. A formal synthesis of (R)-calindol

A N-iodosuccinimide (NIS)-mediated method to prepare 1H-indole-2-carbaldehydes efficiently from cycloisomerization of 1-(2-aminophenyl)prop-2-yn-1-ols is described. The reaction is operationally straightforward and accomplished in good to excellent yields (48-91%) from a wide range of alcohol substrates that are low cost, easily accessible, and ecologically benign. The utility of the approach as a potential scale-up strategy for the synthesis of the indole was exemplified by the large-scale synthesis of one example in an excellent yield. The synthetic utility of this chemistry was also demonstrated in a formal synthesis of (R)-calindol.