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Background  It is well established that vicinal fluorines (RCHF-CHFR) prefer to adopt a  gauche  rather than an  anti  conformation when placed along aliphatic chains. This has been particularly recognised for 1,2-difluoroethane and extends to 2,3-difluorobutane and longer alkyl chains. It follows in these latter cases that if  erythro  and  threo  vicinal difluorinated stereoisomers are compared, they will adopt different overall conformations if the fluorines prefer to be  gauche  in each case. This concept is explored in this paper with  erythro - and  threo - diastereoisomers of 2,3-difluorosuccinates.    Results  A synthetic route to 2,3-difluorosuccinates has been developed through  erythro - and  threo - 1,2-difluoro-1,2-diphenylethane which involved the oxidation of the aryl rings to generate the corresponding 2,3-difluorosuccinic acids. Ester and amide derivatives of the  erythro - and  threo - 2,3-difluorosuccinic acids were then prepared. The solid and solution state conformation of these compounds was assessed by X-ray crystallography and NMR.  Ab initio  calculations were also carried out to model the conformation of  erythro - and  threo - 1,2-difluoro-1,2-diphenylethane as these differed from the 2,3-difluorosuccinates.    Conclusion  In general the overall chain conformations of the 2,3-difluorosuccinates diastereoisomers were found to be influenced by the fluorine  gauche  effect. The study highlights the prospects of utilising the vicinal difluorine motif (RCHF-CHFR) as a tool for influencing the conformation of performance organic molecules and particularly tuning conformation by selecting specific diastereoisomers ( erythro  or  threo ).

beilstein journal of organic chemistry

The vicinal difluoro motif: The synthesis and conformation of <i>erythro</i>- and <i>threo</i>- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives