No abstract

We report herein a simple alternative method for the asymmetric transfer hydrogenation (ATH) of 1‐aryl‐3,4‐dihydroisoquinolines (1‐Ar‐DHIQs) that are known to be challenging substrates owing to their poor reactivity. The hydrogenation protocol employs the readily available Cp*Ir(TsDPEN) {where Cp* = pentamethylcyclopentadienyl and TsDPEN = (S,S)‐HNCHPhCHPhNTs2–} catalytic complex, 2‐propanol and HCOOH/triethylamine mixture as the solvent and hydrogen donor, and anhydrous phosphoric acid as an inexpensive additive. The series of examined substrates shows a favorable tolerance to various functional groups. Unlike 1‐alkyl‐DHIQs, where the enantiomeric excess (ee) starkly changes during the course of hydrogenation, 1‐Ar‐DHIQs exhibit a constant ee value, which makes the method practical and useful for the production of fine chemicals containing the 1,2,3,4‐tetrahydroisoquinoline motif.