Ru(II)‐Catalyzed Hydroarylation of in situ Generated 3,3,3‐Trifluoro‐1‐propyne by C−H Bond Activation: A Facile and Practical Access to β‐Trifluoromethylstyrenes

In this study, a practical and straightforward synthesis of β‐( E )‐trifluoromethylstyrenes by ruthenium‐catalyzed C−H bond activation was developed. The readily available and inexpensive 2‐bromo‐3,3,3‐trifluoropropene (BTP), a non‐ozone depleting reagent, was used as a reservoir of 3,3,3‐trifluoropropyne. With this approach, the monofunctionalization of a panel of heteroarenes was possible in a safe and scalable manner (23 examples, up to 87 % yield). Mechanistic investigations and density functional theory (DFT) calculations were also conducted to get a better understanding of the mechanism of this transformation. These studies suggested that 1) a cyclometallated ruthenium complex enabled the transformation, 2) this complex exhibited high efficiency in this transformation compared to the commercially available [RuCl 2 ( p ‐cymene)] 2 and 3) the mechanism proceeded through a bis‐cyclometallated ruthenium intermediate for the carboruthenation step.