Rhodium(Ⅲ)-Catalyzed Chemoselective Reduction Of α,β-unsaturated Aromatic Ketones

Selective hydrogenation or conjugate reduction of transition metal catalyzed unsaturated aromatic ketone compounds is an attractive and important class of reactions in organic synthesis.Saturated aromatic ketone compounds after selective hydrogenation have a wide range of applications in medicine,pesticides,flavors and fragrances and other fields.Hydrogen is still the main source in hydrogenation and industrial production.However,hydrogen poses a huge potential safety hazard.It is imperative to find a relatively safe and clean hydrogen source to replace hydrogen.This project uses pentamethylcyclopentadienyl rhodium as a catalyst for the selective reduction of unsaturated aromatic ketones for the first time,useing relatively safe isopropanol as hydrogen source.This project was the first to use dichloro(pentamethylcyclopentadienyl)ruthenium(III)dimer as a catalyst,using isopropanol as a hydrogen source to achieve the selective reduction of unsaturated aromatic ketones.In the presence of competitive reduction of olefins and carbonyl groups,carbonyl functional groups are retained,selectively reducing carbon-carbon double bonds.This research has enriched the selective reduction system.According to the selective hydrogenation reduction of carbon-carbon double bonds of unsaturated aromatic ketene compounds,chalcone was firstly used as a template material,and a series of conditions such as solvent,temperature,and catalyst were used to optimize the determination.ultimately determine the optimal conditions were follows:pentamethylcyclopentadienyl rhodium dimer(3.0 mol%)was regarded as catalyst and isopropanol(1.0 mL)was regarded as hydrogen source and solvent.Under argon conditions,the mixture was stirred and heated at 100 ℃ for 12 h.Under these conditions,the chalcone conversion was 100%and the yield of 1,3-diphenylpropan-1-one was 94%.Based on experimental results and related literature,a possible reaction mechanism was proposed.Different types of unsaturated aromatic ketene compounds were synthesized and the substrate generality of the reaction was investigated under the optimal conditions.The experimental results show that the reactive functional group has good compatibility.The steric hindrance effect and electron effect have little effect on the reaction,and the reaction selectivity is good.The yield is as high as 98%.The products were identified by 1H NMR,13C NMR,Fourier infrared and other characterizations as corresponding target products.Based on the wide application of saturated aromatic ketone compounds in life,an effective method for the selective reduction of unsaturated aromatic ketones to saturated aromatic ketones was developed in this paper.The target product is obtained with high selectivity and moderate to good yield,which has a certain degree of innovation and potential application value and provides a new approach for the selective conversion of unsaturated aromatic ketone compounds.