Primary OH group

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

The primary OH group can be selectively blocked by the bulky triphenyl-methyl (trityl) moiety, followed by esterification at the secondary OH groups and removal of the protecting trityl group. Thus 2,3-di-O-acetyl cellulose has been obtained by this procedure. Moreover, regioselectively substituted mixed cellulose esters, acetate/propionate, were prepared by subsequent acy-... 

Sulfonic esters are most frequently prepared by treatment of the corresponding halides with alcohols in the presence of a base. The method is much used for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (10-21). Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to N,N-disubstituted sulfonamides that is, R" may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually R 0 . However, R" may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate HC(OR)3, without catalyst or solvent and with a trialkyl phosphite P(OR)3. ... 

Fig. 27 Chemoselective oxidation of primary OH-groups in carbohydrates with TEMPO as mediator [143-145],...

The redox and complexation chemistry of alditol/Cr(VI) systems64 and the my<9-inositol/Cr(VI) system65 has been reported. In the first case, when an excess of the alditol over Cr(VI) is used, the secondary OH groups are inert to oxidation, and alditols are selectively oxidized at the primary OH group to yield the aldonic acid as the only oxidation product. The corresponding reaction involves a Cr(VI) —> Cr(V) —> Cr(III) reduction pathway, and the relative rate of each step depends on [H+] at... 

However, when bulky electrophilic species are used, such as chlorotrimethylsi-lane or highly substituted silyl chlorides, the primary alcohols at positions 6 and 6 react faster, the more hindered OH-T being less reactive because of its proximity to the quaternary carbon atom C-2.63 65 The trisilyl ether of all three primary OH groups is formed when tcrt-b u ty 1 d i phenylsilyl chloride (TBDPSC1) is used in excess. In the presence of 1.1 equiv. of TBDPSC, significant regio-selectivity is observed in favor of 6-OH, since the 6 -monoether can be obtained... 

Note that this structure also illustrates the linkage to silica through one primary -OH group. Either one or two such linkages usually attach the substrate to the silica. The numbers (2, 3, and 6) indicate the three points on each of the subunits where subsequent phase modification can take place. 

The reaction is performed under dry conditions. 40.5 g l,2-diphenyl-l-[4-[2-(N,N-dimethylamino)ethoxy]phenyl]butane-l,4-diol and 150 ml of acetic acid anhydride are placed in a flask. The temperature is raised to 90°C, where it is kept until the primary OH-group is completely acetylated. [4-Acetoxy-1,2-... 

The most common types of lipids are esters of glycerol. Glycerol is just propane-1,2,3-triol but it has interesting stereochemistry. It is not chiral as it has a plane of symmetry, but the two primary Oh[ groups are enantiotopic (Chapter 16), If one of them is changed—hy esterification, for example—the molecule becomes chiral. Natural glycerol phosphate is such an ester and it is optically active. 

The cavity of p-CD, with a diameter of about 7 A, provides an attractive binding site for the substrate on the side of the primary OH groups. Benzaldehyde enclosed in the hydrophobic cavity of a thiamine-functionalized p-CD was first converted to a thiazolium adduct having a similarity to a cyanohydrin (Figure 4). This adduct readily formed a benzylic anion, as evidenced by fhe anion s characteristic reactions such as deuterium exchange and oxidation. 

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