AI Article Synopsis
- The fluorine atom, being very small, can still contribute to the stability of certain chiral compounds when neighboring groups have high steric demand.
- Two specific compounds, which feature ortho-fluoro groups, were identified as some of the first examples of N-aryl axially chiral molecules with isolated enantiomers.
- A study involving these compounds showed that reactions with alkyl halides revealed differences in how the steric influences of hydrogen versus fluorine atoms affected the reaction outcomes, specifically highlighting the role of steric demand in chemical selectivity.
Article Abstract
The fluorine atom is the second smallest atom; nevertheless, the ortho-fluoro group may lead to stable N-aryl atropisomers when the steric demand of the flanking substituents is large enough. 2-Alkyl-3-(2-fluorophenyl)quinazolin-4-ones and 3-(2-fluorophenyl)-4-methylthiazoline-2-thione were found to be the first N-aryl axially chiral compounds bearing an ortho-fluoro group whose enantiomers were isolated at ambient temperature. The reaction of alkyl halides with the anionic species prepared from 2-ethyl-3-(2-fluorophenyl)quinazolin-4-one presenting an N-C axial chirality provided a model reaction for quantitative evaluation of the steric discrimination (slight difference of steric factor) between hydrogen and fluorine atoms. In the case of low steric demand (allylation reaction) no diastereoselectivity was detected, while in the case of high steric demand (isopropylation reaction) the diastereoselectivity became significant.
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| http://dx.doi.org/10.1021/acs.joc.8b03043 | DOI Listing |
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