Our research program is focused on the design and development of transition metal catalysts capable of high selectivity in organic chemical transformations that extend from intermolecular reactions to macrocyclizations. Focus is placed on pharmaceutical applications.
We have developed chiral catalysts that are effective for a broad range of metal carbene and Lewis acid catalyzed transformations. None are as general in their applications as dirhodium(II) compounds that possess four chiral carboxamidate ligands. Optical yields at or greater than 95% have been achieved in intramolecular cyclopropanation reactions with allyl diazoacetates and diazoacetamides, in alkyne cyclopropenation reactions, and in gamma-lactone production from carbon-hydrogen insertion reactions of diazoacetate esters, including those of lignan lactones, deoxysugar derivatives, and other pharmaceutically active compounds. Diastereoselectivity, regioselectivity, and chemoselectivity are high, and enantiomer differentiation is achieved with exceptional ease.
Catalyst turnover is high, especially in scale-up, and when immobilized on polymer supports, the recoverable dirhodium(II) catalyst retains its effectiveness in eight or more sequential transformations. The basis for the high level of enantiocontrol that has been achieved with the use of these dirhodium(II) carboxamidates is attributed to the organization of the four chiral amide ligands around the dirhodium nucleus and stabilization of the intermediate metal carbene.
Previously regarded as selective only for the formation of five- and six-membered ring ketones and lactones in intramolecular reactions, transformations of diazocarbonyl compounds catalyzed by select rhodium(II) and copper(I) compounds have been broadly extended to the production of ten- to twenty-membered rings with high chemoselectivity, as well as enantio- and regiocontrol. Enantiocontrol is also high with these catalysts in hetero-Diels-Alder reactions where record low catalyst loadings are required (<0.01 mol % catalyst). Extension to other reactions is underway.