Some observations on the formation of 1‐hydroxyindoles in the leimgruber‐batcho indole synthesis

The factors influencing the formation of 1‐hydroxyindoles in the catalytic hydrogenation of β‐dimethylamino‐2‐nitrostyrenes (Leimgruber‐Batcho indole synthesis) have been investigated. Significant amounts of 1‐hydroxyindoles were obtained only when the β‐dimethylamino‐2‐nitrostyrene was substituted with an electron‐withdrawing group at the 5 or 6 position. The proportion of 1‐hydroxyindole formed relative to the normal indole product was found to increase as both the amount of catalyst and hydrogen pressure were decreased.