Experimental and theoretical evidence of through-space electrostatic stabilization of the incipient oxocarbenium ion by an axially oriented electronegative substituent during glycopyranoside acetolysis

摘要

The rate of acetolysis of methyl 2,3,6-tri-0-methyl-α-D-galacto- and -glucopyranosides depends strongly on the electronegativity of the C4 substituent. Thus, of the three derivatives studied (4- methoxy, 4-acetoxy, and 4-acetamido-4-deoxy derivatives of D-galacto- and D-glucopyranbosides), the glycopyranosides bearing the most electronegative C4 substituent (methoxy roup) acetolyze at the fastest rate, whereas those having the least electronegative C4 substituent (N-acetamido group) acetolyze at the slowest rate.