Recent Progress in Iridium-Catalyzed Enantioselective Hydrogenation: Tetrasubstituted Olefins and Polyenes

Iridium-catalyzed enantioselective hydrogenation has become the method of choice to convert prochiral unfunctionalized olefins to optically active compounds. Recently, we reported on applications giving access to more than one stereocenter in a single hydrogenation step. In this account we present recent developments in the hydrogenation of tetrasubstituted unfunctionalized olefins and isoprenoid polyenes, which allow the generation of two stereocenters in a single hydrogenation step

NeoPHOX - a structurally tunable ligand system for asymmetric catalysis

A synthesis of new NeoPHOX ligands derived from serine or threonine has been developed. The central intermediate is a NeoPHOX derivative bearing a methoxycarbonyl group at the stereogenic center next to the oxazoline N atom. The addition of methylmagnesium chloride leads to a tertiary alcohol, which can be acylated or silylated to produce NeoPHOX ligands with different sterical demand. The new NeoPHOX ligands were tested in the iridium-catalyzed asymmetric hydrogenation and palladium-catalyzed allylic substitution. In both reactions high enantioselectivities were achieved, that were comparable to the enantioselectivities obtained with the up to now best NeoPHOX ligand derived from expensive tert-leucine

Determining the Enantioselectivity of Chiral Catalysts by Mass Spectrometric Screening of Their Racemic Forms

The enantioselectivity of a chiral catalyst can be determined from its racemic form by mass spectrometric screening of a nonequal mixture of two mass-labeled quasienantiomeric substrates. The presented method opens up new possibilities for evaluating catalyst structures that are not readily available in enantiomerically pure form

Enantio-and regiocontrol in palladium-and tungsten-catalyzed allylic substitutions

Abstract: Tungsten catalysts with chiral phosphinooxazoline ligands react with 3-aryl-2-propenyl diethyl phosphates and the sodium salt of dimethyl malonate to give the corresponding chiral substitution products with regioselectivities of 3-24: 1 and 88-96% ee. A new class of chiral P,N-ligands has been developed which allow efficient regio-and enantiocontrol in analogous Pd-catalyzed allylic substitutions of 1-and 3-aryl-2-propenyl acetates with dimethyl malonate

Application of tethered ruthenium catalysts to asymmetric hydrogenation of ketones, and the selective Hydrogenation of aldehydes

An improved method for the synthesis of tethered ruthenium(II) complexes of monosulfonylated diamines is described, together with their application to the hydrogenation of ketones and aldehydes. The complexes were applied directly, in their chloride form, to asymmetric ketone hydrogenation, to give products in excess of 99% ee in the best cases, using 30 bar of hydrogen at 60 °C, and to the selective reduction of aldehydes over other functional groups

Synthesis of functionalized pyridinium salts bearing a free amino group

Tetrasubstituted N-methylpyridinium salts bearing a free tertiary amino group have been synthesized by a straightforward procedure starting from inexpensive starting materials. The key feature of the synthesis is the use of a proton as a simple effective protecting group to achieve selective N-methylation of the pyridine ring without attacking the amino group

Control of Metal-Catalyzed Reactions by Organic Ligands: From Corrinoid and Porphinoid Metal Complexes to Tailor-Made Catalysts for Asymmetric Synthesis

Corrinoid and porphinoid metal complexes playa fundamental role in nature as catalysts for a variety of biochemical transformations. The properties of the metal ion in these complexes are strongly influenced by the macrocyclic ligand. In this way, the reactivity of the metal complex is adjusted to the specific requirements of enzymatic catalysis. This is illustrated in the first part of this article, which is centered on the structure and properties of coenzyme F430, a hydroporphinoid nickel complex involved in the methane-producing step of the energy metabolism of methanogenic bacteria. A different group of metal complexes, which exemplify the concept of ligand-based selectivity control, is discussed in the second part, summarizing our work on enantioselective catalysis. Inspired by the structure of corrinoid and hydroporphinoid compounds, we have developed a route to chiral C2-symmetric semicorrins, a particular class of bidentate nitrogen ligands specifically designed for the stereocontrol of metal-catalyzed reactions. Semicorrins were found to induce remarkable enantioselectivities in the cobalt-catalyzed conjugate reduction of ?,?-unsaturated carboxylic esters and amides and in the copper-catalyzed cyclopropanation of olefins with diazo compounds