Aminocatalyzed Cascade Synthesis of Enantioenriched 1,7‐Annulated Indoles from Indole‐7‐Carbaldehyde Derivatives and α,β‐Unsaturated Aldehydes

Abstract We report herein a new cascade strategy for the enantioselective synthesis of 1,7‐annulated indoles based on iminium‐enamine activation. A careful study of the indole substitution pattern revealed that a chloro substituent at the C‐3 position was important to the implementation of the reaction. Employing a diphenylprolinol silyl ether catalyst, a range of 3‐chloro‐1 H ‐indole‐7‐carbaldehyde derivatives reacted with α,β‐unsaturated aldehydes to afford the corresponding 1,7‐annulated indoles in good yields (62–99%) and enantioselectivities (62–92%). Besides the fluorescence properties of the 1,7‐ring fused indoles prepared following our methodology, these compounds contain a useful set of functional groups which undergo various synthetic transformations. magnified image