Example 29
Scheme 7 illustrates the incorporation of the azido moiety into building block 2, prepared as described in example 7.
Compound 5 (building block 2) was reacted with Cl3CCN in the presence of a catalytic amount of DBU in the presence of dichloromethane to give trichloroimidate 8. Trichloroimidate 8 was reacted under Schmidt glycosylation conditions to give compound 14. Compound 14 was synthesized in 70% overall yield.
Scheme 8 illustrates the synthesis of 2-azidoethylgentiotetrose.
Compound 14 was deprotected by treatment of borontrifluoride etherate complex in methanol to give compound 15. Compound 3 (building block 1) was treated with trichloroacetonitrile and catalytic DBU to give compound 11. Compound 14 and compound 11 then subjected to the Schmidt glycosylation conditions to afford the gentiotetrose product 16. The overall yield of the sequence was 60%.
