Diastereoselective Rhodium-Catalyzed Hydrogenation of 2-Oxindoles and 3,4-Dihydroquinolones.

The benzene ring of indolin-2-ones (2-oxindoles) and 3,4-dihydroquinol-2-ones was converted to a saturated cyclohexane ring by hydrogenation in the presence of the rhodium complex Cy(CAAC)Rh(cod)Cl. The stereoselectivity of the process was found to be high with respect to both external substituent R1 within the saturated part of the heterocyclic ring and substituent X on the benzene ring. Twenty-one hexahydroindolin-2(3H)-ones (70-99% yield, dr = 83/17 to >99/1) and twelve octahydro-2(1H)-quinolinones (87-96% yield, dr = 64/36 to >99/1) were obtained with the major diastereoisomer exhibiting the hydrogen atoms in an all-cis arrangement. The high tolerance toward functional groups and the compatibility with existing stereogenic centers are key features of the hydrogenation protocol presented here.