THE ALCOHOLYSIS OF TRIALKYLALKOXYSILANES: PART I. A KINETIC STUDY OF THE METHANOLYSIS OF METHYL 2,3,4,6-TETRA-O-TRIMETHYLSILYL-α-D-GLUCOPYRANOSIDE TO FORM METHYL 2,3,4-TRI-O-TRIMETHYLSILYL-α-D-GLUCOPYRANOSIDE

Abstract

The selective methanolysis of the trimethylsilyl group on the primary 6-position of methyl 2,3,4,6-tetra-O-trimethylsilyl-α-D-glucopyranoside (I) to form methyl 2,3,4-tri-O-trimethylsilyl-α-D-glucopyranoside (II) is catalyzed by acid or base. In the latter case the reaction follows second-order kinetics in I and methoxide ion, and the rate of reaction is independent of the nature of the cation of the metal methoxide used to catalyze the reaction. Successive replacement of the methyl hydrogens in the methoxide ion by methyl groups is accompanied by a corresponding decrease in the rate of reaction. The rate constant for removal of trimethylsilyl groups at the secondary 2-, 3-, and 4-positions of I and II is smaller by a factor of 25 than for removal of the corresponding group at the primary 6-position, and the energies of activation for the two processes are 10.8 and 9.1 kcal mole⁻¹.