Convenient preparation of 2-phenylethyl 3,3-difluoro-2-methylpropionate
The slow inverse addition of an LDA solution at -78 °C to an ester of 2-(trifluoromethyl)acrylic acid enabled efficient dehydrofluorination. Hydrogenation of the resulting difluoromethylacrylate furnished the target ester of 3,3-difluoro-2-methylpropionic
Effect of allylic CH3-nFn groups (n = 1-3) on π-facial diastereoselection
(equation presented) Michael addition of various enolates toward γ-CH3-nFn-α,β-unsaturated ketones (n = 1-3) was proven to smoothly furnish the 1,4-adducts with high si face selectivities which monotonously decreased by reduction in the number of fluorines. Although the Felkin-Anh model correctly anticipates the present stereochemical outcome only with E-acceptors, the hyperconjugative stabilization of transition states by electron donation from the allylic substituents (the Cieplak rule) successfully explains the π-facial preference of both acceptors at least in a qualitative level.