Reactions of glycyrrhetic acid derivatives with trifluoromethyl hypofluorite. Preparation of a new triterpenoid system

Selective Fluorinations by Reagents Containing the OF Group

“…Regio-and stereoselective addition was recorded also with complex molecules such as glycyrrhetic acid where the decomposition of the adduct led to a rare 1,3-sigmatropic methyl shift (Scheme 8). 21 In some special cases, where a relatively stable R-fluorocarbocation is formed, a cationic rearrangement is observed at -78 °C, which further supported the ionic notion (Scheme 9). 22 Patrick's work on the addition of the fluoroxytrifluoromethane to 1,1-diphenylethene and 9-ethylidenefluorene (Scheme 10), 23 and the corresponding Hammett F values of the reaction of CF 3 OF with various styrenes at -78 °C (Scheme 11), 24 pointed to a tandem radical-ionic addition mechanism despite the low dipole moment of 0.3 D this reagent possesses.…”

“…The syn addition is typical of most reactions with electrophilic fluorine since they proceed through the very unstable α-fluorocarbocation which collapses before the anion has a chance to diffuse out of the reaction cage (Scheme 7). Regio- and stereoselective addition was recorded also with complex molecules such as glycyrrhetic acid where the decomposition of the adduct led to a rare 1,3-sigmatropic methyl shift (Scheme 8) . In some special cases, where a relatively stable α-fluorocarbocation is formed, a cationic rearrangement is observed at −78 °C, which further supported the ionic notion (Scheme 9) …”