Secondary 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-... 

Answer An inversion ts now necessary, so we must make the tosylate of the secondary OH group before reducing the ester, Diborane will reduce the ester In this case... 

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... 

Sebacic acid is important as a component for compatible polyesters, especially in combination with higher glycols like 1,3- or 1,4-butanediol. Secondary OH-groups in the ortho position, of the glycol decrease compatibility. 

Mortellaro et al. prepared two (3-CD derivatives, which have a bromonaph-thalene unit at the primary (1) and secondary OH groups (2) of (3-CD [27], The phosphorescence of 2 at 530 nm is more than 100 times intense than that observed for an equimolar solution of 1. These results suggest that the bromonaphthalene moiety of 2 is protected from oxygen quenching, being located inside the CD cavity, whereas the bromonaphthalne moiety of 1 is not protected, being exposed into bulk solution. 

It is well known 6 8, Ul that different side reactions may occur during the thermosetting of epoxides. This may lead to many differences in the chemical and physical structure of a final polymer. The main side reaction proceeding in a polymer under Tcure > 130 -140 °C22) is the reaction between secondary OH groups and unreacted epoxy rings ... 

This looks a strange reaction but it is really quite logical. One of the secondary OH groups must be oxidized to a ketone. This is tire 2-OH group and then the resulting ketone can simply enolize to give ascorbic acid. 

Now for the unravelling. The same intermediate (open-chain aldehyde) is involved but the hemiacetal is formed with a different secondary OH group. There are many ways to vvork this out. [ he front OHs sta the same, of course vou just Iiave to twist tiie back round. 

Triisopropylsilyl chloride (TIPS-Cl) is an excellent reagent for the selective protection of a primary OH in the presence of a secondary OH group. ° A simple and efficient method for silylation of alcohols and phenols is using TIPS-Cl and imidazole under microwave irradiation. The TIPS group is stable under a wide range of reaction conditions, such as acid and basic hydrolysis, and toward powerful nucleophiles. 

A simple, convenient method for the selective acylation of a primary OH in the presence of a secondary OH group is its conversion into the t-butanoyl ester (also known as a pivalate ester, OPv). Moreover, the steric bulk of the t-butyl group makes these esters resistant to nucleophilic attack, including hydrolysis under mild basic conditions. The pivalate ester can be cleaved using metal hydride reagents. 

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