A convenient synthesis of lacto-N-biose I [β-d-Galp-(1 → 3)-β-d-GlcpNAc] linked oligosaccharides from phenyl O-(tetra-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-4,6-di-O-acetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside☆