| Summary: | 碩士 === 靜宜大學 === 應用化學研究所 === 95 === Reaction of cyclic enol ethers such as 2,3-dihydrofuran(DHF) 6 and 3,4-dihydro-2H-pyran(DHP) 7 with a variety of alcohols catalyzed by using 0.1 equivalent of iodotrimethylsilane(Me3SiI), generated in situ from Me3SiCl and NaI, afforded a series of O-tetrahydrofuranyl(O-THF) ether 8 and O-tetrahydropyranyl (O-THP) ether 9 in high yields, respectively. Similarly, this method was applied to 3,4,6-tri-O-acetyl- D-glucal (TAG) 4 and 3,4,6-tri-O-benzyl-D-glucal (TBG) 5, a series of 2-deoxy sugars 12 and 14 as major product, and a series of 2,3-unsaturated O-glycosides 13 and 15 as minor product. The -anomers were predominated.
Reaction of TAG with a variety of -dicabonyls 16 catalyzed by using 0.5 equivalent of iodine molecule afforded a series of 2,3-unsaturated C-glycosides 17 as major product and cycloaddition adducts 18 as minor, respectively; the -anomers were also predominated. The proposed mechanism is that after the formation of 2,3-unsaturated oxonium intermediate via Ferrier’s rearrangement from TAG the enol form of -dicarbonyls was proceeding the nucleophilic addition. Experimental results demonstrated that the reactivity of cyclic -dicarbonyls is higher than acyclic -dicarbonyls; and the obtained products such as 17g and 17h exhibit the enol form.
Reaction of TAG with a variety of -dicabonyls 16 mediated by using 3.5 equivalents of iodine molecule afforded a series of cycloaddition adducts 18 as predominate. The proposed mechanism is that the carbon-carbon double bond between C-2 and C-3 in 2,3-unsaturated C-glycosides 17 could be induced by iodine molecule to form the bridged iodonium ion, in which the enol form of -dicarbonyl was proceeding the intramolecular cyclization.
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