HYDROFORMYLATION OF OPTICALLY PURE MONOTERPENES CATALYZED BY DINUCLEAR THIOLATO-BRIDGED RHODIUM COMPLEXES

The low-pressure hydroformylation of di-or trifunctionalized cyclic mo noterpenes was carried out with the dinuclear rhodium complexes [Rh-2( mu-(SBu)-Bu-1)(2)(CO)(2)L-2] under 5-13 bar (1 bar = 10(5) Pa). The ex ocyclic ethylenic double bond of R-limonene, S-carvone, S-perillyl alc ohol, or (1R,4R)-isolimonene was rather easily and selectively carbony lated. Attempts to induce high diastereoselectivities gave a 22% diast ereoisomeric excess (d.e.) under the best conditions. On the other han d, cyclization following the hydroformylation of (1R,2S,5R)-isopulegol allowed a good 64% d.e. This reaction does not require the presence o f chiral phosphorus ligands. The asymmetric induction is directed by t he substrate configuration. Under slightly higher pressures (13-20 bar ), (-)-beta-pinene and (-)-camphene were selectively carbonylated and d.e. values ranging from 26 to 85% were obtained with classical phosph ite or diphosphine ligands. Finally, at 100 bar, (-)-alpha-pinene and (-)-myrtenol were transformed with moderate yields and selectivities b ut high d.e. of up to 100%.