Glycosylation of lactose. Synthesis of methyl O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl-(1→4)-β-d-glucopyranoside and methyl O-β-d-galactopyranosyl-(1→4)-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-O-β-d-galactopyranosyl- (1→4)-β-d-glucopyranoside