CYCLIC ENEDIOL PHOSPHORANES OBTAINED FROM THE REACTION OF TRIMETHYL PHOSPHITE WITH BIACETYL AND HEXAFLUOROBIACETYL GIVE STRIKINGLY DIFFERENT ACYLATION PRODUCTS

Article abstract of DOI:10.1016/S0040-4020(01)91291-8

Cyclic enediol phosphoranes (2,2,2-trimethoxy-2,2-dihydro-1,3,2-dioxaphospholenes), prepared from α-diketones, RCOCOR, and trimethyl phosphite (TMP), give strikingly different acylation products depending on the electronic properties of the groups, R, that occupy the 4,5-positions in the dioxaphospholene ring with pentacovalent phosphorus.Reaction of acetyl chloride or bromide with hexafluorobiacetyl-TMP phosphorane gives exclusively the product of endocyclic O-acylation, dimethyl-(2-acetoxy-cis-1,2-bistrifluoromethylvinyl) phosphate.Acylation of the biacetyl-TMP phosphorane gives mixtures of the product of exocyclic O-acylation (a cyclic enediol phosphate) and the product of C-acylation (an α-hydroxy-β-diketone phosphate), the proportions depending on the structure of the acyl halide and the solvent.The parent 1,2,3-dioxaphospholene, i.e., the glioxal-TMP phosphorane where R=H, gives exclusively the product of endocyclic O-acylation with both acyl halides in all solvents.