Pentoses tritylation

The hemiacetal hydroxyl group is more reactive than the other secondary ones. Thus, trityl 5-0-tritylpentopyranosides are obtained from pentoses when an excess of trityl chloride [290] or elevated temperature [291] is used. For D-lyxose, the ditrityl derivative is formed considerably even at room temperature with only one molar equiv. of the reagent. Under such conditions, the other three pentoses give the 5-trityl ethers in ca. 60% yields [291]. Further re-investigation of the monotritylation of D-xylose at 50 °C revealed the 5-, 4-, 3-, and 1- substitution in the ratio [292] of 100 25 0 36. 

A systematic examination of the tritylation of pentoses by Zeile and Kruckenberg resulted in the isolation of ditrityl ethers of D-xylose and... 

The selective tritylation of pentoses has been studied, and providing that the reaction is conducted at below 25 C and with only one equivalent of trityl chloride, the 5-0-tritylate is the major product. However, even under these conditions lyxose afforded substantial amounts of diethers, and the 5-monoether was isolated in only 32% yield. The monotritylation of D-xylose has been studied in detail at 50 °C in the presence of either pyridine or AgOAc-HMPT, and four of the monotrityl ethers were isolated as tetra-O-acetyl derivatives. The ratio of 1-, 3-, 4-, and 5-substitution was 36 0 25 100 (in pyridine) and 0 49 57 100 (AgOAc-HMPT). The products were also prepared unequivocally by the tritylation of the appropriate D-xylose tetra-acetate. The selective tritylation of methyl a- and j3-L-rhamnosides has also been studied the a-anomer giving the 3-, 4-, and 2-trityl ethers in 57, 3, and 1% yields respectively. The j3-anomer afforded the 3- and 4-trityl ethers in 34 and 17% yields respectively. Pyridinium perchlorate has been used for the selective de-O-tritylation of otherwise peracetylated methyl gluco- and manno-pyranosides. ... 

Deoxy-2-iodoascorbic acid L.-form, D-252 2"-Deoxy-5-iodouridine 3"-Ac, D-278 2"-Deoxy-5-iodouridine 3",5"-Di-Ac, D-278 2"-Deoxy-5-iodouridine 5"-Tosyl, D-278 2"-Deoxy-5-iodouridine 5"-Trityl, 3 -Ac, D-278 2"-Deoxy-5-iodouridine 5"-Trityl, D-278 2"-Deoxy-5-iodouridine, D-278 2"-Deoxyisoguanosine, 1-51 2"-Deoxy-3-methylcytidine, 9CI, D-43 2"-Deoxy-5-methylcytidine, D-295 2-Deoxy-3- O -methy -i>-arabino -hexose, D-199 2"-Deoxy-iV-(2-nietliyl-l-oxopropyl)guanosine, 9CI, D-360 9-(2-Deoxy-eryi/iro-pentofuranosyl)adenine a-D-form, D-339 9-(2-Deoxy-eryi/ira-pentofuranosyl)adenine a-L-/orm, D-339 2-Deoxy- 7i/ira-pentopyranosyl fluoride a-D-form Dibenzoyl, D-343 2-Deoxy-er> /Aro-pentopyranosyl fluoride p-D-/orm Dibenzoyl, D-343 2-Deoxy-/Areo-pentopyranosyl fluoride -D-form Dibenzoyl, D-344 2-Deoxy-er> /Aro-pentopyranosyl fluoride a-D-form, D-343 2-Deoxy-/Areo-pentopyranosyl fluoride p-D-/orm, D-344 2-Deoxy-er> /Aro-pentose D-form 3,5-0-Benzylidene, di-Et dithioacetal, D-345... 

Deoxy-4-thiothyniine, D-341 2 -Deoxy-4 -thiouridine, D-378 2-Deoxy-5-0-trityl-D-cr /Aro-pentose, D-345 2 -Deoxyuridine, D-382 2-Deoxy-D-xylono-1,4-lactone, D-674... 

In the pentose series methyl 4-Q- -D-xylopyranosyl -D-xylopyranoside has been synthesised by glycosylation of a methyl 4-Q-trityl- -D-xylopyranoside derivativeDetailed C n.m.r. studies of the methyl 0-D-xylopyranosyl-/3-D-xylopyranosides have been reported. ... 

Remarkably, a general inversion of internal diastereoselectivity is observed by deployment of 5-tritylated pentoses 39-42 in these transformations (compare internal diastereoselectivities of Scheme 2.6 with those of Scheme 2.8). 

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