Removal ofO-Benzyl Protective Groups by Catalytic Transfer Hydrogenation

Practical Total Synthesis of (2S,3S,4R)-1-O-(α-D-Galactopyranosyl)-N-hexacosanoyl-2-amino-1,3,4-octadecanetriol, the Antitumorial and Immunostimulatoryα-Galactosylcer-amide, KRN7000

“…using hcxancEtOAc (9: I) as the eluent, to give pure 8 as a solid. (9). To a solution of crude 8 (121 g, ca.…”

Syntheses of O6‐Alkyl‐ and Arylguanine Derivatives: Nucleobase Adducts Derived from Styrene 7,8‐ and 3,4‐Oxides

“…The reaction conditions were analogous to those described by Bieg et al [36] Palladium (10 %) on carbon containing nearly 50 % of water, (Degussa type E101 NE/W) (1.484 g) was activated under vacuum at 110°C. The benzyl-protected derivative (0.300 g, 0.83 mmol) and ammonium formate (0.325 g) in 19 mL of absolute MeOH was added to the catalyst and refluxed for 5-7 h. The total amount of ammonium formate (1.3 g) was added subsequently in four portions.…”

Synthesis of toxyloxanthone B

“…Claisen rearrangement under mild conditions 26 resulted in formation of the fused pyran ring to give protected toxyloxanthone 14 in quantitative yield (Scheme 2). The final step required the removal of three benzyl protecting groups, and although this could not be carried out under catalytic transfer hydrogenation with ammonium formate as hydrogen donor, 27 treatment with boron trichloride in dichloromethane in the presence of pentamethylbenzene 28 at À78 C initially removed two of the benzyl groups. For full deprotection, the reaction mixture required warming to room temperature with extra boron trichloride, which pleasingly gave the xanthone 3a (toxyloxanthone) in 64% yield.…”