Diastereoselective Synthesis of Functionalized Indoline N,O‐Aminals: Unexpected Water‐Involved Cascade Reaction of 3H‐Indoles and Oxazol‐5‐(4H)ones

Herein, we describe an unexpected TsOH·H2O‐mediated domino three‐component reaction of 3H‐indoles, oxazol‐5‐(4H)ones, and water, allowing rapid access to a new family of structurally unique indoline N,O‐aminals bearing a valuable α‐acylaminoamide moiety in high yields and excellent diastereoselectivities. The scaled‐up experiment and various transformations of the products further demonstrate the utility of this chemistry. Moreover, a preliminary study on the catalytic asymmetric version of this novel 1,2‐difunctionalization reaction is performed. A Brønsted acid catalyzed highly diastereoselective three‐component cascade reaction of 3H‐indoles, oxazol‐5‐(4H)ones and water is reported. The reaction proceeds under mild conditions with broad substrate scope to give the desired products in high yields.