In organic chemistry, an orthoester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula RC(OR’)3. Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these than the name 'ortho ester' is derived. An example is ethyl orthoacetate, CH3C(OCH2CH3)3, more correctly known as 1,1,1-triethoxyethane. Orthoesters are used in organic synthesis as protecting groups for esters.
- RCN + 3 R’OH → RC(OR’)3 + NH3
- RC(OR’) 3 + H2O → RCO2R’ + 2 R’OH
For example, trimethyl orthoformate [CH(OCH3)3] may be hydrolyzed (under acidic conditions) to methyl formate and methanol; and may be further hydrolyzed (under alkaline conditions) to salts of formic acid and methanol.
Bodroux–Chichibabin aldehyde synthesis
As a protecting group
Both trimethylorthoacetate and triethylorthoacetate are commonly used reagents in organic chemistry. Another example is the bicyclic OBO protecting group (4-methyl-2,6,7-trioxa-bicyclo[2.2.2]octan-1-yl) which is formed by the action of (3-methyloxetan-3-yl)methanol on activated carboxylic acids in the presence of Lewis acids and was developed by Elias James Corey. The group is base stable and can be cleaved in two steps under mild conditions, mildly acidic hydrolysis yields the ester of tris(hydroxymethyl)ethane which is then cleaved using e.g. an aqueous carbonate solution.
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