A Study On Bioreduction Of 2-Alkyl-4,4,4-trichloro-2-butenals Mediated By Baker's Yeast

Due to its inherent advantages such as the mild reaction conditions and high stereoselectivity, biotransformation has become an efficient way for preparing chiral compounds. In recent years, more and more researchers are devoting themselves into this field. The success of our previous work on the bioreduction of 2-ethylhex-2-enal, a substrate without an 3-aryl group, arouse our interest to further investigate the bioreduction of other aliphatic acroleins.In this thesis,the baker's yeast (whole cell) mediated asymmetric reduction of 2-alkyl-4,4,4-trichloro-2-butenals was studied. 2-Alkyl-4,4,4-trichloro-2-butenals was obtained via dehydration of the aldol products prepared through direct cross-aldol reactions of chloral with aliphatic aldehydes at first. The asymmetric bioreduction of thisα,β- unsaturated aldehyde was next studied in detail. Effects of pH values, reaction mediums, and the reaction time on the yields and the e.e. values of products 2-alkyl-4,4,4- trichloro-1-butanol were evaluated. A high yield of 2-ethyl-4,4,4-trichloro-1- butanol (85%) with excellent enantioselectivity (99%) was afforded in the water-petroleum ether biphasic system.Meanwhile, an unexpected and interesting one-way isomerization of 2-alkyl-4,4,4- trichloro-2-butenals was observed in this work. The substituents at theβ-sites have a marked effect on its isomerization rate.