Tritylation of

The tritylation of 5 was performed in pyridine using standard procedures. Reaction mixtures were worked-up by water quenching followed by filtration and recrystallization of the crude product. Recrystallization of the crude product was done from 2-propanol containing small amounts of triethylamine. The addition of triethylamine was necessary to avoid the formation of trityl isopropyl ether by solvolysis of the product when heated in 2-propanol. The yield of the product in this step was 75-80%. Impurities such as ethyl glyoxylate diethyl acetal carried over from previous steps were removed during the isolation of 6. 

Ozonolysis of 6 to produce 7 was studied at temperatures ranging from -78 to -0 °C in mixtures of dichloromethane and methanol. The intermediates that formed were found to be stable below -30 °C. Diol 7 was obtained in high yields when the reaction mixture was quenched with aqueous sodium borohydride. If the reaction mixture was warmed to room temperature before the quench, a complex mixture of products formed as indicated by the NMR spectrum. Similarly, only polymeric products were formed when the ozonolysis was carried out without methanol even at -78 °C. When ozonolysis was done at -5 to 0 °C in the presence of methanol, formation of trityl methyl ether was noticed, a result similar to which has been observed before [2], Diol 7 was obtained in near quantitative crude yield when ozonolysis was carried out below -30 °C, followed by the addition of the reaction mixture to cold, aqueous sodium borohydride solution. The product was used without further purification in the next step. 

The conversion of 7 to 1 in high yields has previously been described by the Lilly group. The reaction of the diol with methane sulfonyl chloride was carried out in dichloromethane in the presence of triethylamine. The crude product was then recrystallized from a mixture of ethyl acetate and heptane. The reaction can also be carried out in ethyl acetate, eliminating the use of dichloromethane. Care should be exercised to remove all traces of acid from 1 since the trityl group can cleave in the presence of acids, causing the decomposition of the product. The yield of the product in this step was 85-90%. The chemical purity was 99% and ee was 99.5%. 

Enantiomerically enriched hetero Diels-Alder cycloadducts have found applications in the synthesis of other pharmaceutical intermediates such as compactin and mevinolin [4, 5]. The strategy described in this work should be applicable to these and similar compounds. 

3 For a review on hetero Diels-Alder reactions see M.D. Bednarski, J.P. Lissika-tos, in Comprehensive Organic Synthesis, Vol. 2 (B.M. Trost, I. Fleming, 

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TrBr, CHCI3, DMF, it, 0.5-1 h Et3N, it, 50 min." These conditions also lead to tritylation of carboxyl groups in the amino acids, but they can be selectively hydrolyzed. This method was considered to be an improvement over the standard methods of TV-tritylation of amino acids. 

To effect A -tritylation of serine, Me2SiCl2 should be used in the silylation step. 

Mild benzhydrylation (diphenylmethylation) of primary and secondary saccharide alcohols, and tritylation of the primary alcohols, were promoted by 4A AW-300 MS at room temperature through a dehydration mechanism in the absence of any strong protic or Lewis acid. While protection of a single primary or secondary hydroxyl... 

M. Adinolfi, G. Barone, A. Iadonisi, and M. Schiattarella, Mild benzhydrylation and tritylation of saccharidic hydroxyls promoted by acid washed molecular sieves, Tetrahedron Lett., 44 (2003) 3733-3735. 

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. 

Tetramolar tritylation of sucrose in pyridine for 2 days at room temperature gave, after column chromatography on silica gel, 6,6 -di-... 

A practical, large scale preparation of 1 further enhances the usefulness of the authors tritylation procedure.3 The preparation involves N-tritylation of 4-dimethylaminopyridine under mild conditions. Isolation of the product is straightforward and the product may be stored at ambient temperature for extended periods, without degradation. 

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... 

This degradation has also been applied151 to the dextran produced by Leuconostoc mesenteroides NRRL B-512, which is composed of (1 — 6)-linked a-D-glycopyranose residues, about 5% of which carry a side chain linked to 0-3 (partial structure 87). Tritylation of... 

Tritylamines can serve as both linkers and protective groups for aliphatic amines because, unlike benzhydrylamines, they do not usually undergo acylation when treated with activated acid derivatives. Tritylation of aliphatic amines is readily accomplished by adding excess amine to a support-bound trityl chloride. Illustrative cleavage reactions are listed in Table 3.21. 

Histidine and histamine derivatives, as well as other imidazoles, have been successfully immobilized by N-tritylation of the imidazole ring with trityl chloride resin [534] (Entry 2, Table 3.29 see also Section 15.8) or with 2-chlorotrityl chloride resin [535-537]. Histidine can also be linked to insoluble supports as the N-dinitrophenyl deriva-... 

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