Selective reduction of aromatic esters using in-situ-generated?LiBH4

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Theodore Alexander Strayer (Creator)
Western Carolina University (WCU )
Web Site:
William Kwochka

Abstract: Functional group interconversion is an essential strategy in synthetic organic chemistry with some functional groups being more difficult to. The ester functional group is relatively difficult to reduce when compared to aldehydes and ketones. Typically, esters can be reduced to the corresponding primary alcohol using a strong hydride reducing agent like lithium aluminum hydride. Sodium borohydride, a related but weaker hydride reducing agent, is not usually used to reduce esters to alcohols because the reaction is too slow to be practical. Lithium borohydride, however, is lies between lithium aluminum and sodium borohydride in terms of reactivity and can be effectively be employed to selectively reduce esters. Aromatic esters are a bit more difficult to reduce than aliphatic esters due to the enhanced stability provided by the aromatic ring. However, lithium borohydride can be used to reduce aromatic esters as well. In previous work done in the lab, attempted reduction of an aromatic diester using lithium borohydride resulted in the selective reduction on only one of the ester groups. The goal of this research project is to examine the generality and scope of this selective mono-reduction of a variety of aromatic diesters using in situ generated lithium borohydride under a variety of reaction conditions. The aromatic esters examined include the three isomeric dimethyl esters containing a benzene ring, along with the trimethyl ester containing a benzene ring. Additionally, a variety of other reaction conditions were evaluated. Each of the products formed in these reactions were fully characterized by 1 H and 13C NMR, FT-IR, and GC/MS. Both the meta and para isomers of the aromatic diester were effectively mono-reduced but the ortho isomer appeared to not undergo reduction at all. The results for the lithium borohydride reduction of the aromatic triesters, were more ambiguous.

Additional Information

Language: English
Date: 2020
Organic compounds -- Synthesis
Reduction (Chemistry)

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