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Jiang, Tao

Chemistry

2006

PhD

Thirdly, three concise synthetic routes toward the L-daunosamine are presented. Starting from achiral molecule crotonaldehyde, condensation with hydrazine followed by Sharpless asymmetric dihydroxylation reaction affords the diol hydrazone. In the first route, the diol is differentiated first, and an iodoacetal 6-exo radical cyclization results in the formation of L-3-epi-daunosamine derivative as major product. In the second route, the diol hydrazone is modified with two silicon-tethered vinyl groups, and the bis-silyl ether substrate leads to the chiral diol hydrazine upon thiyl addition-cyclization followed by treatment with fluoride. The N-N bond cleavage reaction affords the linear chiral diol amide, and the linear structure in this case is an open-chain derivative for L-daunosamine. Wacker oxidation treatment on the C=C bond results in terminal aldehyde, and subsequent ring closure under acidic conditions affords the sugar molecule L-daunosamine. In the third route, the diol is modified with two silicon-tethered ethynyl groups, and tandem thiyl addition-cyclization on the C=N bond affords (E)-2-(phenylthio) vinyl adduct. The linear adduct in this case is another type of open-chain derivative for L-daunosamine. Treatment with mercuric chloride converts the vinyl sulfide into the aldehyde, and a ring closure reaction affords the L-daunosamine finally with good yield.