Functional-group-directed diastereoselective hydrogenation of aromatic compounds. 2(1)
Diastereoselective liquid-phase hydrogenation of a series of monosubstituted indan substrates was studied on supported rhodium catalysts. Predominantly the cis-cis diastereomer, obtained by hydrogenation from the diastereoface opposite the substituent at the stereogenic center, and the cis-trans diastereomer, obtained by hydrogenation from the diastereoface on the same side as the substituent, were formed. The diastereoselectivity depends on the balance between steric repulsion and electronic attraction of the substituent with the surface of the catalyst. For alkoxy and carboxyl groups (acid, methyl ester, and amide), the steric repulsion dominated and the cis-cis diastereomer was obtained with moderately high selectivity. The diastereoselectivity obtained in the hydrogenation was influenced by the addition of bases to the reaction mixture. Addition of triethylamine caused a small increase in the selectivity to the cis-cis diastereomer in some substrates, whereas the addition of NaOH significantly increased the selectivity toward the cis-trans isomer in all substrates.
Ranade
VS
Laboratory for Technical Chemistry, Swiss Federal Institute of Technology (ETH), CH 8092 Zurich, Switzerland.
Consiglio
G
Prins
R