Hydrogenolysis of Dioxolane-Type Diphenylmethylene Acetals by AlClH₂to Axial Diphenylmethyl Ethers

Synthesis, regioselective hydrogenolysis, partial hydrogenation, and conformational study of dioxane and dioxolane-type (9′-anthracenyl)methylene acetals of sugars

“…However, an opposite directing effect of the free OH-4 next to the acetal ring also appears and gives rise to the formation of the axial ether 20. We demonstrated earlier 15,16 in the course of symmetrical acetals of sugars that an adjacent-free hydroxyl could participate in the opening reaction of the acetal ring. Being a free hydroxyl present at the acetal derivative first the reagents reacted with the OH free forming an aluminate derivative, then the cleavage of the acetal occurred through an intramolecular complexation of the adjacent oxygen of the acetal ring.…”

Block Synthesis of Tetra- and Hexasaccharides (β-d-Glycero-d-manno-Hepp-(1→4)-[α-l-Rhap-(1→3)-β-d-glycero-d-manno-Hepp-(1→4)]n-α-l-Rhap-OMe (n = 1 and 2)) Corresponding to Multiple Repeat Units of the Glycan from the Surface-Layer Glycoprotein from Bacillus thermoaerophilus

“…Two l -rhamnopyranosyl acceptors 16 and 17 were prepared by protection of the corresponding triols as the benzophenone acetals19 in moderate yield (Scheme 3). Somewhat better yields of 16 and 17 have been reported in the literature for alkylation of 14 and 15 with dichlorodiphenylmethane in pyridine.…”

“…Somewhat better yields of 16 and 17 have been reported in the literature for alkylation of 14 and 15 with dichlorodiphenylmethane in pyridine. 19a…”

“…The organic phase was washed with brine, dried over Na 2 SO 4 , and concentrated. The residue was purified by flash chromatography on silica gel (AcOEt/hexane = 1/5to1/4) to afford 16 19a (1.29 g, 3.8 mmol, 47%). [α] D 24 = − 71.6 ( c 0.65, CHCl 3 ); 1 H NMR (500 MHz, CDCl 3 ) δ 7.53-7.51 (m, 4 H), 7.34-7.27 (m, 6 H), 5.02 (s, 1 H), 4.28 (t, 1 H, J = 6.5 Hz), 4.06 (d, 1 H, J = 5.5 Hz), 3.71-3.66 (m, 1 H), 3.42-3.39 (m, 1 H), 3.38 (s, 3 H), 2.28 (br s, 1 H, OH ), 1.27 (d, 3 H, J = 6.0 Hz); 13 C NMR (125 MHz, CDCl 3 ) δ 143.1, 142.7, 128.4, 128.3, 126.3, 126.2, 109.8, 98.3, 79.1, 76.1, 74.1, 66.2, 55.2, 17.3; HR-ESI m/z : calcd for C 20 H 22 O 5 Na, 365.1365 [M+Na + ]; Found C 20 H 22 O 5 Na, 365.1353.…”

“…Following the protocol for 16 , treatment of thioglycoside 15 25 (1.60 g, 6.2 mmol) with benzophenone dimethyl acetal24 (2.84 g, 12.5 mmol) and camphorsulfonic acid (81 mg, 0.35 mmol) furnished alcohol 17 19a (1.03 g, 2.4 mmol, 39%). [α] D 24 = − 191.0 ( c 1.2, CHCl 3 ); 1 H NMR (500 MHz, CDCl 3 ) δ 7.54-7.47 (m, 6 H), 7.46-7.25 (m, 9 H), 5.91 (s, 1 H), 4.34 (dd, 1 H, J = 5.5, 7.0 Hz), 4.29 (d, 1 H, J = 6.0 Hz), 4.14-4.09 (m, 1 H), 3.45-3.40 (m, 1 H), 2.14 (br s, 1 H), 1.19 (d, 3 H, J = 6.5 Hz); 13 C NMR (125 MHz, CDCl 3 ) δ 143.2, 142.9, 133.6, 132.3, 129.3, 128.5, 128.4, 127.9, 126.2, 126.0, 109.8, 83.8, 79.3, 77.1, 74.9, 67.2, 17.3; HR-ESI m/z : calcd for C 25 H 24 O 4 NaS, 443.1293 [M+Na + ]; Found C 25 H 24 O 4 NaS, 443.1277.…”