Highly selective ring-opening of 1,3,3-trihalogenoepoxycyclohexanes by boron trihalides; methodology for the determination of the regioselectivity in the cyclisation of 2,2,6,6-tetrahalogenocyclohexanols

Beyond the Balz–Schiemann Reaction: The Utility of Tetrafluoroborates and Boron Trifluoride as Nucleophilic Fluoride Sources

“…The efficient regio- and stereoselective ring-opening fluorination of a number of 1,3,3-trihalogeno-7-oxabicyclo[4.1.0]­heptanes 243 with BF 3 ·OEt 2 has been accomplished by Duhamel and co-workers . The reactions were conducted with 0.53–0.55 equiv of BF 3 ·OEt 2 in 1,2-dichloroethane (DCE) at reflux, and gave the corresponding fluorohydrins 245 in excellent yield with retention of configuration (five examples, 60–98% yield).…”

Ring-Opening Hydrofluorination of 2,3- and 3,4-Epoxy Amines by HBF4·OEt2: Application to the Asymmetric Synthesis of (S,S)-3-Deoxy-3-fluorosafingol

“…However, many of the existing methodologies for stereoselective fluorination suffer from economical or practical setbacks, often relating to the fluorinating agents themselves. Considering the significant benefits (i.e., low cost, high fluorine content, and ease of handling in standard glassware), we recently embarked upon investigations into the utility of BF 3 ·OEt 2 as a nucleophilic fluorine source and reported the stereoselective ring-opening hydrofluorination of substituted aryl epoxides with BF 3 ·OEt 2 under mild conditions for the synthesis of β-fluoroamphetamines . For instance, treatment of β-methylstyrene oxide ( R , R )- 1 (∼90% ee) with 0.33 equiv of BF 3 ·OEt 2 in CH 2 Cl 2 at −20 °C for 5 min gave syn -fluorohydrin 2 as the major product in 81% isolated yield, >99:1 dr, and 92% ee, consistent with a stereoselective S N 1-type process that results in retention of configuration.…”

Intramolecular OH⋅⋅⋅FC Hydrogen Bonding in Fluorinated Carbohydrates: CHF is a Better Hydrogen Bond Acceptor than CF2

“…These H-bonds persist to about 70 % in [D 8 ]THF and to 35-40 % in [D 6 ]DMSO. [36] The data however inform that the two equatorial F atoms lead to reduction of 3 J(1,OH) to 6.6 Hz and to the complete disappearance of the 1h J(OH,F) coupling. Such a tetravalent H-bond is also present in the solid state of d/l-19 [27] (see X-ray structure in the Supporting Information).…”