Tetrahedron Letters p. 4949 - 4953 (2000)
Update date:2022-08-04
Topics: Glycosides Preparation of (2-naphthyl)methylene acetals Hydrogenolytic transformation 2-naphthylmethyl (NAP) ethers
Lipták, András
Borbás, Anikó
Jánossy, Lóránt
Szilágyi, László
Dioxane- and dioxolane-type (2-naphthyl)methylene acetals of glycosides were prepared by acid-catalyzed transacetalization reactions. The acetals were cleaved using either AlH3 (LiAlH4:AlCl3-3:1), NaCNBH3-HCl or BH3·Me3N-AlCl3 reagents. Reaction of the 4,6-O-acetals with AlH 3 yielded 4-ONAP ethers whereas the other two reagents gave 6-ONAP derivatives with excellent regioselectivity. In dioxolane, type acetals the direction of the cleavage with all three reagents is determined by the stereochemistry of the acetal center; equatorial ONAP/axial-hydroxy derivatives are obtained from the exo-naphthyl isomers; endo-naphthyl acetals, on the other hand, give rise to the formation of axial ONAP/equatorial-hydroxy compounds. The NAP ether and the (2-naphthyl)methylene acetal protecting groups can both be readily removed by treatment with DDQ. (C) 2000 Elsevier Science Ltd.
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