Study On Selective Reduction Of Carbon-Carbon Double Bond Of α, β-Unsaturated Carbonyl Compounds

As we all know, saturated carbonyl compounds play an important role in the production of medicine, hormone, spice, food additive and agrochemicals. We need to selective reduction ofα,β-unsaturated carbonyl compounds in order to saturated carbonyl compounds. In other words, it must be possible to selectively reduce the conjugate double bonds under appropriate conditions, and the other function need not be reduced. It has always been a challenging problem in organic synthesis.Numerous methodologies of selective reduction ofα,β-unsaturated carbonyl compounds have been reported in the literature, for example, Pd, Rh, Pt, Ni, Ir, Co and their complexes. They have available vacant d orbital which accept and receive electron. Therefore, their oxidation state and coordination number are reversible. They have special electronic effect and spatial effect when coordinate the organic compound. Furthermore, hydrides of Sn, Se, Te, B, sodium dithionite and sodium borohydride were also reported to be useful for the hydrogenation ofα,β-unsaturated carbonyl compounds. Catalysis of yeast species has been studied too. Although these systems are effective, they suffer from their own limitations: hash reaction condition, indispensable agents, complicated manipulations, long reaction time and low yield or low functional selectivity. Therefore, the development of a mild and selective reducing agent for the conjugate reduction ofα,β-unsaturated carbonyl compounds still attract a great deal of attention of organic chemists. In our work, we try to find a simple selective reduction system. We study on the selective reduction of the carbon-carbon double bonds ofα,β-unsaturated esters, amides, ketones. The saturated compounds have been characterized by elemental analysis, IR, 1H-NMR.This paper consists of four parts.Part I. Recent developments of selective reduction of the olefinic bonds inα,β-unsaturated carbonyl compounds are reviewed, including theα,β-unsaturated aldehyde, ketones, acids, esters, amides, The developing trend and broad application prospects are also discussed.Part II. A reducing system, NaBH4-CuCl/CH3OH, was applied for the selective reduction of carbon-carbon double bond ofα,β-unsaturated esters with high selectivity. Effects of the amount of NaBH4 and CuCl, solvent, different halide on the reaction were investigated in order to the best conditions. This method is easy operation, high yields, easy prognostic disposed.Part III. The study on the selective reduction ofα,β-unsaturated amides. A facile procedure for the conjugate reduction ofα,β-unsaturated amides is reported with NaBH4/CuCl in ethanol at ambient temperature. The merits lie in excellent yields, inexpensive reagent, simple operation and environmentally friendly.Part IV. The study on the selective reduction of substituted chalcones. A reducing system, Zn/NH4Cl/C2H5OH/H2O, was applied for the selective reduction of carbon-carbon double bond of chalcones without catalyst and harsh condition. The results indicate that the process has the merits of safety, easy operation, higher yields, short reaction time, simple apparatus and so on. It expends the reaction using low-cost zinc metal as reductant in the organic synthesis.