Abstract
In a thermal inverse-type hetero-Diels-Alder reaction of O-protected lactal 1 and bis(2,2,2-tri-chloroethyl) azodicarboxylate ( 2), the dihydrooxadiazine derivative 3 was obtained in a very high yield; transesterification with benzyl alcohol furnished the corresponding derivative 4. Treatment of 3 with methanol in the presence of BF 3·OEt 3 afforded the methyl lactoside derivatives 5 which, after transesterification with benzyl alcohol, then hydrogenolytic debenzylation and concomitant NN-cleavage with Raney nickel, and N-acetylation, furnished methyl O-(2,4,6-tri- O- tert-butyldimethylsilyl-β- d-galactopyranosyl)-(1 → 4)-2-acetamido-3,6-di- O- tert-butyldimethylsilyl-2-deoxy-β- d-glucopyranoside ( 7) in high yield. Desilylation of 4, then O-acetylation, methyl glycoside formation with methanol-BF 3·OEt 2, hydrogenolytic debenzylation, and NN-cleavage with Raney nickel, and N-acylation afforded methyl O-(2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1 → 4)-2-acetamido-3,6-di- O-acetyl-2-deoxy-β- d-glucopyranoside ( 10).
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