Pyridinium dichromate-Acetic anhydride

Another highly versatile building block derived from diacetone-glucose 54 is the 1,2-acetonide of 3-C-methyl-a-D-allose in its furanoid form 57, which has been utilized as the key compound in a convergent total synthesis of ACRL Toxin I (63). Its elaboration from 54 starts with a pyridinium dichromate / acetic anhydride oxidation (64), is followed by carbonyl olefination of the respective 3-ulose with methyl (triphenyl)phosphonium bromide and hydrogenation (— 55 56), and is completed by acid cleavage of the 5,6-isopropylidene group. This four-step process 54 -> 57, upon optimization of reaction conditions and workup procedure, allows an overall yield of 58 % (63), as compared to the 22 % obtained previously (65). 

Pyridinium dichromate (15.64 g, 41.6 mmol) was suspended in a mixture of 320 mL dry CH2CI2 and 11.8 mL acetic anhydride (124.8 mmol). A solution of 11.11 g l-O-methyl-3,5-di-0-benzyl-Q, /3-D-ribofuranose-3,4,5,5 - H4 (32.0 mmol) in dry CH2CI2 was added to the suspension, and the reaction mixture was refluxed at 80°C for 3 h. After the dilution with EtOAc, a precipitate was formed, and the solution was Altered through silica gel using EtOAc as the eluent. The solvents were evaporated, and the residue was co-evaporated with toluene to give 7.93 g l-0-methyl-3,5-di-(9-benzyl-a, 3-D-ribofuranose-2-ulose-3,4,5,5 - H4 as an oily product (23.0 mmol, 72%), which was taken to the next step without further puriflcation. 

Related Reagents. A/-Chlorosuccinimide-Dimethyl Sulfide Chromic Acid Dimethyl Sulfide-Chlorine Dimethyl Sulfoxide-Acetic Anhydride Dimethyl Sulfoxide-Dicyclo-hexylcarbodiimide Dimethyl Sulfoxide-Oxalyl Chloride Dimethyl Sulfoxide-Phosphorus Pentoxide Dimethyl Sulfoxide-Sulfur Trioxide/Pyridine Dimethyl Sulfoxide-Trifluoroacetic Anhydride Dimethyl Sulfoxide-Triphosgene Manganese Dioxide Pyridinium Chlorochromate Pyridinium Dichromate Ruthenium(rV) Oxide Silver(I) Carbonate on Celite 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3( 1 H)-ons. 

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