RCH(OMEM)CFBr2 with n-BuLi at −130 °C in the presence of 4-heptanone gives the corresponding adduct diastereoselectively. The stereochemical outcome is explained in terms of the chelation between lithium and oxygen atoms of the MEM group. Starting with 2-phenylpropanal, a product is produced highly selectively containing three contiguous stereocenters including a -CFBr- moiety.
Generation and Carbonyl Addition Reactions of Dibromofluoromethyllithium Derived from Tribromofluoromethane as Applied to the Stereoselective Synthesis of Fluoro Olefins and 2-Bromo-2-fluoro-1,3-alkanediols
3 was converted stereoselectively to (E)-1-bromo-1,2-difluoro olefin 5 via fluorination with Et2NSF3, followed by dehydrobromination with lithium 2,2,6,6-tetramethylpiperidide, while (E)-1-bromo-1-fluoro olefin was obtained with high selectivity by acetylation of 3, followed by reductive elimination using EtMgBr/(i-Pr)2NH. Difluoro olefin 5 underwent a cross-coupling reaction with an aryl, alkenyl,