Tf 2 O‐Mediated Multicomponent Reactions of Enaminones with Acylacetonitriles and Ammonium Acetate to Access 5,6‐Dihydrobenzo[ h ]quinolines

A Tf 2 O‐mediated three‐component reaction of enaminones, acylacetonitriles, and ammonium acetate has been developed for the efficient synthesis of 5,6‐dihydrobenzo[ h ]quinolines. This transition‐metal‐ and oxidant‐free protocol leverages electrophilic activation of enaminones by Tf 2 O to facilitate a straightforward cascade cyclization. The reaction demonstrates broad substrate scope, tolerating a wide range of aryl, heteroaryl, and alkyl acylacetonitriles, as well as both cyclic and acyclic enaminones with diverse substituents, to afford the target products in 30–97% yields across 33 examples. Notably, the strategy enables divergent synthesis of dihydrobenzo[ h ]quinolines from cyclic enaminones and trisubstituted pyridines from their acyclic counterparts. Mechanistic studies, including isolation of a key 1,2‐addition intermediate, reveal a reaction pathway initiated by vinyl iminium triflate formation, underscoring the critical role of Tf 2 O in the cyclization step.