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Ethylene glycol protects a ketone (as an acetal) during an ester reduction, vs. unprotected reduction to a diol. A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction.
Generic structure of acetals. In organic chemistry, an acetal is a functional group with the connectivity R 2 C(OR') 2. Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each ...
In carbohydrate chemistry carbohydrate acetalisation is an organic reaction and a very effective means of providing a protecting group. The example below depicts the acetalisation reaction of D-ribose 1. With acetone or 2,2-dimethoxypropane as the acetalisation reagent the reaction is under thermodynamic reaction control and results in the ...
Acid catalyzed acetal formation from the corresponding hemiacetal. Acetals, as already pointed out, are stable tetrahedral intermediates so they can be used as protective groups in organic synthesis. Acetals are stable under basic conditions, so they can be used to protect ketones from a base. The acetal group is hydrolyzed under acidic conditions.
Benzylidene acetals are used as protecting groups in glycochemistry. [1] [2] These compounds can also be oxidized to carboxylic acids in order to open important biological molecules, such as glycosaminoglycans, to other routes of synthesis. [3] They arise from the reaction of a 1,2- or 1,3-diols with benzaldehyde. Other aromatic aldehydes are ...
In organic chemistry, an acetonide is the functional group composed of the cyclic ketal of a diol with acetone. The more systematic name for this structure is an isopropylidene ketal. Acetonide is a common protecting group for 1,2- and 1,3-diols. [1] The protecting group can be removed by hydrolysis of the ketal using dilute aqueous acid.
The ketal is produced by acid catalysed reaction with ethylene glycol, the reduction reaction carried out, and the protecting group removed by hydrolysis to produce 4-hydroxymethylcyclohexanone. NaBArF 4 can also be used for deprotection of acetal or ketal-protected carbonyl compounds.
The reaction is commonly performed using the 1,3-dithiane. The lithiated intermediate can be used for various nucleophilic bond-forming reactions, and then the dithioketal hydrolyzed back to its carbonyl form. This overall process, the Corey–Seebach reaction, gives the synthetic equivalent of an acyl anion.