291314-23-3Relevant academic research and scientific papers
Preparation of (2-naphthyl)methylene acetals of glycosides and their hydrogenolytic transformation into 2-naphthylmethyl (NAP) ethers
Lipták, András,Borbás, Anikó,Jánossy, Lóránt,Szilágyi, László
, p. 4949 - 4953 (2000)
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.
Dioxane-type (2-naphthyl)methylene acetals of glycosides and their hydrogenolytic transformation into 6-O- and 4-O-(2-naphthyl)methyl (NAP) ethers
Borbás, Anikó,Szabó, Zoltán B,Szilágyi, László,Bényei, Attila,Lipták, András
, p. 5723 - 5732 (2007/10/03)
α-, β-D-Gluco-, galacto-, 2-deoxy-2-phthalimido-β-D-glucopyranosides with different aglycons (methyl, allyl, p-methoxyphenyl, thioethyl) reacted with 2-naphthaldehyde dimethyl acetal to give rise to 4,6-O-(2-naphthyl)methylene acetals. The acetals were converted into fully protected compounds bearing benzoyl, benzyl, allyl, p-methoxybenzyl groups. The fully alkylated dioxane-type acetals were hydrogenolysed with AlH3 (3LiAlH4-AlCl3) reagent to furnish 4-O-NAP/6-OH derivatives. All acetals were treated with BH3·Me3N-AlCl3 in THF and a reverse regioselectivity was observed, producing 6-O-NAP/4-OH derivatives. Similar regioselectivity was also observed by using NaCNBH3-HCl reagent. In all reactions very mild reaction conditions were required, regioselectivity was better than 93:7, and the isolated yields were between 83-92%. All compounds were characterised by 1H and 13C NMR spectra. Solid-state and solution conformation of methyl 2,3-di-O-acetyl-4,6-O-(2-naphthyl)methylene-α-D-galactopyranoside were elucidated by X-ray and NMR measurements.
