Regioselective Hydrogenation of α,β-Unsaturated Ketones over Wilkinson’s Catalyst

Abstract

Regioselective Hydrogenation of a,b-Unsaturated Ketones over Wilkinson's CatalystR e g i o s e l e c t i v e H y d r o g e n a t i o n o f a , b -U n s a t u r a t e d K e t o n e s Abstract: The reactivity of a variety of a,b-unsaturated acyclic and cyclic ketones towards regioselective hydrogenation in the presence of Wilkinson's catalyst was determined. Hydrogenation of sterically hindered a,b-unsaturated ketones proceeded at inefficient rates, if at all.

Kinetic and Mechanistic Studies of the Selective Hydrogenation of (E)‐Chalcones in Biomass‐Derived γ‐Valerolactone Catalyzed by Rh−PPh3 Complexes

“…First, we have studied the effects of the most important reaction parameters, such as the ligand/Rh ratio, temperature and H 2 pressure in the hydrogenation of CHL ( 1 a) on the yield (conversion, X/%) and selectivity. The latter proved to be 100 % to DHC ( 2 a ) in all of the cases, similar to that observed with the covalent species [17b] . The influence of the ligand/Rh ratio on the yield was investigated in several experiments at 60 °C under 50 bar of H 2 pressure for 5 hrs.…”

“…Thus, hydrogen is also involved in the rate determination using this cationic system (Scheme 3). Similar pressure dependence and the applied too low initial hydrogen pressures were probably the reasons for the reported fast drop in the activities with the Wilkinson analog [17b] . The hydrogenation reaction rate increases with temperature in the expected extent (Table 2).…”

“…Remarkable initial activities were achieved in the fully chemoselective hydrogenation of α,β‐unsaturated ketones including CHL, 1 a to DHC, 2 a , albeit with rather low yields, by using the Wilkinson's complex, Rh(PPh 3 ) 3 Cl in dichloromethane at 80 °C, under 20 bar of total pressure [17b] . When 10 bar of total pressure was applied at this temperature, hardly any activity was observed.…”