STEREOSELECTIVE REDUCTION OF DISUBSTITUTED AROMATICS ON COLLOIDAL RHODIUM

Hydrogenation of disubstituted aromatic rings can be achieved under mi ld reaction conditions in a two-phase system in presence of RhCl3 and phase transfer agents such as trioctylamine. The catalytic system was optimized for the 2-methylanisole reduction by a proper choice of the amine/Rh ratio which should be high enough to stabilize very small col loidal rhodium particles and low enough to avoid deactivation. A high chemoselectivity and a high stereoselectivity to the Z isomer are obta ined. Moreover enantioselective reductions of o-cresol derivatives wer e performed with colloidal rhodium stabilized and modified by chiral a mines. Diastereoselective reductions were also obtained using chiral a uxiliaries bound to the substrate.