Tritylation selective

The two primary hydroxyl groups in maltose and its derivatives show a large difference in reactivity. On selective tritylation, /3-maltose,238 benzyl /3-maltoside,239 and methyl 3-0-(methylsulfonyl)-/3-maltoside127 all gave mainly 6 -0-trityl compounds. Tritylation of cyclohexaamylose130 and amylose132,240 yielded the expected 6-0-trityl derivatives. 

Novel macrobicyclic compounds have been prepared (151) from the tetraol obtained on de-O-benzylidenation of the bisgalactosido-18-crown-6 derivative aa-DD-117 in Figure 18. Selective tritylation of the two hydroxymethyl groups of the tetraol, followed by a base-promoted reaction with pentaethylene glycol ditosylate afforded aa-DD-155 with a polyether chain bridging the 4 and 4 positions of the D-galactopyranosidic rings across presumably the /3 face of the molecule. 

Micheel then slightly modified his synthesis, starting from D-galactose diethyl dithioacetal (19) (Scheme 2).33 Selective tritylation of the 6-hydroxyl group followed... 

Selective tritylation of methyl oc-L-rhamnopyranoside yielded 57% of the 3-0-trityl derivative, together with 1 % of the 2-0- and 3 % of 4-0-trityl isomers. For methyl P-L-rhamnopyranoside, 34% of the 3-trityl and 17% of the 4-trityl ether were obtained [315]. Similarly, the 3,6-ditrityl ether is the major product of ditrityl-ation of methyl and benzyl a-D-mannopyranosides [316]. The corresponding a-D-glucopyranosides yielded the 2,6-di-O-trityl derivative, whereas both the 2,6- and 3,6-ditrityl ethers were isolated in the case of [Pg.237]

A combination of trityl tetrafluoroborate or perchlorate with 2,4,6-tri(/err-butyl)-pyridine instead of pyridine enables an almost quantitative tritylation of the secondary hydroxyl group in l,2 5,6-di-0-isopropylidene-a-D-glucofuranose in 10 min at room temperature [321]. The more readily available 2,6-di(/m-butyl)-4-methylpyridine was used [322] in combination with trityl perchlorate for the selective tritylation of methyl 2,6-di-0-acetyl-a-D-galactopyranoside at the equatorial OH-3. Combination... 

The imidazole derivative 31 was transformed to bicyclic analogs by selective tritylation at the nitrogen and the primary hydroxyl groups followed by benzylation and then detritylation to give 33 [71]. When the benzylation was carried out at lower temperatures followed by detritylation, the dibenzyl derivative 32 was obtained. Both 32 and 33 were readily cyclized by the action of triflic anhydride in pyridine and chloroform to give 34 and 35, respectively as imidazole analogues of 6-epicastanosperimine and 3,7a-diepialexine. 

Silylation, Tritylation, and Sulfinylation of Alcohols. Tritylation, including selective tritylation of a primary alcohol in the presence of a secondary one, silylation of tertiary alcohols, selective silylation to i-butyldimethylsilyl ethers, and sulfonylation or sulfinylation of alcohols proceed more readily in the presence of DMAP. Silylation of /3-hydroxy ketones with Chlorodiisopropy-Isilane in the presence of DMAP followed by treatment with a Lewis acid gives diols (eq 4). ... 

Selective benzoylation (and allylation) of methyl (and benzyl 4-O-benzyl-a-L-rhamnopyranoside (4) has been studied by phase-transfer catalysis and by activation via the tributyl stannate. The former reaction gave the 2,4-dibenzyl ether (5) in high yield, whereas the latter process gave mainly the 3,4-diether (6). An alternative means of obtaining the 2,4-diether (5) involved selective tritylation to give (7) followed by benzylation and removal of the trityl group. These dibenzyl ethers have been employed in the synthesis of the tetrasaccharide repeating unit of the immunodeterminant of Klebsiella serotype K36 polysaccharide. Similar results have been recorded for the selective benzylation of other 4,6-blocked a-mannosides. The syntheses of 3-O-benzyl-D-ribose, 2-0-benzyl-D-ribose, and l,6-anhydro-2,3,2, 4-tetra-0-benzyl-jS-lactose have been recorded. The latter was employed in the synthesis of lacto-A -tetraose. ... 

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. ... 

Protection of amine groups by tritylation in peptide synthesis s. 11,39 selective— Trityl as N- and S-protective group s. 12, 455 ... 

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