Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 71, Issue 8, Pages 3064-3070Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jo0526789
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- NIGMS NIH HHS [GM57335, R01 GM057335] Funding Source: Medline
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2-O-Propargyl ethers are shown to be advantageous in the 4,6-O-benzylidene acetal directed beta-mannosylation reaction. The effect is most pronounced when the 03 protecting group is a bulky silyl ether or a glycosidic bond; however, even with a 3-O-benzyl ether, the use of a 2-O-propargyl ether results in a significant increase in diastereoselectivity. The beneficial effect of the propargyl ether is thought to be a combination of its minimal steric bulk, as determined by a measurement of the steric A-value and of its moderately disarming nature, as reflected in the pK(a) of propargyl alcohol. Conversely, the application of a 3-O-propargyl ether in the benzylidene acetal directed mannosylation has a detrimental effect on stereoselectivity, for which no explanation is at present available. Deprotection is achieved by base-catalyzed isomerization of the propargyl ether group to the corresponding allenyl ether, followed by oxidative cleavage with N-methylmorpholine N-oxide and catalytic osmium tetroxide.
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