Use of carbohydrate derivatives for studies of phosphorus stereochemistry. Part 7. Stereochemistry of alkoxide-induced ring-opening of 1,3,2-dioxaphosphorinan-2-ones, and of migration of alkyl alkyl phosphoryl groups between the 4- and 6-positions of glucose

Abstract

Cyclic glucose 4,6-(ethyl phosphates) undergo ring-opening in dilute sodium methoxide to afford glucose 4-(ethyl methyl phosphates) as the kinetically favoured products. Ring-opening occurs with preponderant inversion of configuration. On storage in sodium methoxide glucose 4-(ethyl methyl phosphates) afford glucose 6-(ethyl methyl phosphates) with retention of configuration at phosphorus. The stereochemical results for the ring-opening and migration reactions are fully consistent with the intermediacy of trigonal bipyramidal intermediates, which break down by apical departure of the leaving group before pseudorotation or after simple pseudorotational sequences. The configurations at phosphorus of the glucose 4(R)- and 4(S)-, and 6(R)- and 6(S)-(ethyl methyl phosphates) are established by independent synthetic sequences.