ABSTRACT
Background Of the 298,876 registered uorinated structures in the Beilstein Chemical Database (for 2005) only 279 compounds contain a genuine vicinal diuoro motifCHF-CHF-and only 12 crystal structures of this motif are deposited in the Cambridge Structure Data Base. e relatively rare presence of this motif may partly be attributed to the diculty of their selective synthesis. It remains a synthetic challenge to prepare vicinal diuorocompounds eciently and particularly in a stereoselective manner. ere are attractive reasons to explore this motif. It is well known that the conformation of 1,2-diuoroethane is inuenced by the uorine gauche eect, where the uorines prefer to be gauche rather than anti to each other [1]. is preference extends to 2,3-diuorobutane [2], and we have shown that erythro-and threo-9,10 diuorostearic acids have very dierent physical properties [3], the origin of which appears to lie in the dierent conformational preferences associated with the vicinal diuoro-motif for each diastereoisomer. Early
synthetic methods to vicinal diuoro compounds have involved direct uorination of alkenes with for eg. elemental uorine (F2) [4] or XeF2 [5]. Such methods however are either dicult to carry out in a standard laboratory environment or they suer from very poor stereoselectivity. e direct conversion of vicinal diols to vicinal diuorides has been explored with some success. For example both erythro and threo stereoisomers of dimethyl 2,3-diuorosuccinic acid were obtained either from methyl esters of the L-tartrate 1 or the meso-tartrate 1 by treatment with SF4/HF (Scheme 2) [6,7].
