Transfer hydrogenation and transfer hydrogenolysis. X. Selective hydrogenation of methyl linoleate by indoline and isopropyl alcohol

The selective hydrogenation of methyl linoleate was studied using indoline and isopropyl alcohol as hydrogen sources. Many transition metal compounds and metallic palladium were examined as catalysts. High selectivity to monoenes and little formation oftrans isomers were realized under mild conditions in some reaction systems. For example, the system in which isopropyl alcohol and RuCl2(PPh3)3 were used as hydrogen donor and catalyst was excellent. Also in the hydrogen transfer from indoline to the linoleate catalyzed by PdCl2 and (NH4)2PdCl4, high selec‐tivity was realized. In the RuCl2(PPh3)3‐isopropyl alcohol, (NH4)2PdCl4‐indoline and PdCl2‐indoline system, methylcis‐ trans conjugated octadecadienoate was reduced rapidly with complete selectivity, where‐as the same hydrogen transfer systems resulted in little if any reaction with methyl oleate. High selec‐tivity in the reduction of linoleate is presumed to be realized through prior conjugation of the substrate.