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

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• , rather than compound 16 which would have a trans relationship and a much larger 3JHF coupling constant (~30 Hz), and reinforces the stereochemical assignment made to 14 as illustrated in Scheme 5 [21]. Substitution of the bromine in anti-14 with fluorine was accomplished by treatment with Ag(I)F in

• pot process with NBS, PPHF and Ag(I)F again proceeded smoothly however it also gave erythro-13 as the major product of the reaction, although with a reduced diastereoisomeric ratio (47% de) more suitable for threo- 13 isolation. The bias towards erythro- 13 in this case is clearly a result of internal