Note
The Koenig+Knorr reaction of benzyl 4,6-O-benzylidene-fl-o-galactopyranoside with 2,3,4,6-tetra-O-acetyl-a-D-galactopyranosyl bromide In continuation of our studiesle5 on the relative reactivity ot' HO-2 and -3 in 4,6-O-benzylidene-D-glucopyranosides towards u-glucosylation 111 reactions of the Koenig+Knorr type, we report hcrc the determination of the ratio of 3-to 3-Osubstitution in benzyl 4.6-0-benzylrdene-li-u-galactopyrano f I ) tou:trds 7,?,4,6tetra-0-acetyl-r-v-galactopyranosyl bromide (5). in a silver carhonatc-promited. Koenig+Knorr reaction, by careful isolation of the disaccharide deli\ atlvcs formed. After this work had been completed, Corin' reported that the r;ltio of 2-to 3-Osubstitution in methyl 3.6-O-benzylidene-/I-r,-g3lactopyr~~~~~~side (2 I totvards 5 in a similar, silver carbonate-assisted reaction is _ 2 : 3. ab dctcrmined from the ' 'C-n.m.r. spectrum of a mixture of the (142 )-and (I -+3)-/i-u-linked dismharrde dtxivatives. OAc 5 Because 1 is sparingly soluble in the solvents that are commonly used in the Koenigs-Knorr condensation', I, 1,2,'-tetrnchloroethanc was used as the solvent. Treatment of 1 with 1.3 mol. eyuiv. of 5 in I,1 ,_,_ 7 7-tetrachloroethane at JO*, in the presence of silver carbonate and Drieritr, ~CLIT 9 mixture that ~a sho~\n by t.1.c. to contain two disaccharide derivatives and unreacted 1.