De-O-tritylation

The Ireland s)mthetic intermediate 176 was deoxygenated by the Barton procedure to provide 194 (O Scheme 22). Stepwise deprotection and protection of hydroxy groups in 194 afforded 195. De-O-tritylation and Swem oxidation of 195 gave the C10-C15 segment 192. As shown in Scheme 22, this aldehyde was transformed into the C10-C20 segment 197. 

Trifluorocetates. Alkenes undergo the presence of V2O5 at reflux temperatun De-O-tritylation. Trityl ether cleai CF3C00H-(CFiC0)20 without affectinj functionalities. 

De-O-tritylation. Trityl ether cleavage can be performed by treatment with CF3C(X)H-(CF3C0)20 without affecting other reducible and acid-hydrolyzable functionalities. 

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. ... 

---

See also in sourсe #XX -- [ ]

---