Process Mass Intensity (PMI) for (a) process in organic solvents, (b) process in water with surfactants.

Choose the right ligand: An iridium complex derived from a phosphino–imidazoline ligand is a highly efficient catalyst for the asymmetric hydrogenation of terminal vinyl boronic esters (see scheme). On the other hand, trisubstituted alkenyl‐boronates can be reduced with high activity and good to excellent enantioselectivity employing a pyridine–phosphinite ligand.

Dedicated to Prof. Antonio Togni on the occasion of his 65th birthday Iridium catalysts with chiral P,N ligands have greatly enhanced the scope of asymmetric olefin hydrogenation because they do not require a coordinating group near the C=C bond like Rh and Ru catalysts. Pyridophos ligands, possessing a conformationally restricted annulated pyridine framework linked to a phosphinite group, proved to be particularly effective, inducing high enantioselectivities in the hydrogenation of a remarkably broad range of substrates. Here we report the development of an efficient scalable synthesis for the two most versatile Ir-pyridophos catalysts, derived from 2-phenyl-8-hydroxy-5,6,7,8-tetrahydroquinoline or the analogue with a fivemembered carbocyclic ring, respectively, by modification and optimization of the original synthetic route. The optimized route renders both catalysts readily accessible in multi-gram quantities in analytically pure form in overall yields of 26-37 %, starting from acetophenone and cyclopentanone or cyclohexanone, respectively. A major advantage of the new synthesis is the efficient and practical kinetic resolution of the late-stage pyridyl alcohol intermediates with commercial immobilized Candida antarctica lipase B, giving access to both enantiomers of these catalysts as essentially enantiopure compounds. The catalysts are obtained as crystalline solids, which are air-stable and can be stored for years at À 20°C without notable decomposition.

Iridium-catalyzed asymmetric hydrogenation has emerged as a highly efficient method for the synthesis of enantiomerically pure compounds. This account summarizes our recent efforts in this field. We have developed a new type of P, O-ligand that was successfully applied to the asymmetric hydrogenation of α,β-unsaturated carbonyl compounds. Furthermore we have demonstrated the potential of known iridium catalysts in the hydrogenation of α,β-unsaturated boronic esters. And finally we could demonstrate the utility of iridiumcatalyzed asymmetric hydrogenation in the formal synthesis of the natural product Platensimycin.

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