Studies On Pinacol Coupling Reactions

Recent Progress in the synthesis of pinacols via the coupling of aldehydes and ketones is reviewed. And we have researched the pinacol coupling reactions in sunlight and ultrasound irradiation. This thesis consists of four parts.Part 1: Progress in the synthesis of pinacols via the coupling of aldehydes and ketones. Several methods about pinacol coupling reactions have been reviewed, these methods including: pinacol coupling reactions with metals or metallic complexes under stirring, photochemical methods, electrochemical methods, and the effect of ultrasound irradiation on the pinacol coupling reactions.Part 2: Pinacol coupling of aromatic aldehydes mediated by Zn powder in acid aqueous media under ultrasound irradiation can lead to the corresponding pinacols in 14-88% yields.Part 3: Complexes of titanium tetrachloride and tetrahydrofuran in CH2Cl2 can be reduced by Zn or Al to corresponding low valent titanium complexes, which can reduce some aromatic aldehydes to corresponding pinacols in 33%-98% yield at r.t. within 4-25 min.Part 4: Reductive coupling of aromatic aldehydes and ketones leading to piancols has been achieved with high yield in isopropanol in sunlight. The notable advantage of the present method seems to be the negligible formation of side products arising mainly due to reduction of the carbonyls to the corresponding alcohols, Cannizzaro reaction and the formation of olefins.