Orthoester
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 that 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.
Orthoesters can be prepared by the Pinner reaction, in which nitriles react with alcohols under acid catalysis:
Orthoesters are readily hydrolyzed in mild aqueous acid to form esters:
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.
The Johnson–Claisen rearrangement is the reaction of an allylic alcohol with an orthoester containing a deprotonatable alpha carbon (e.g. triethyl orthoacetate) to give a γ,δ-unsaturated ester.
In the Bodroux–Chichibabin aldehyde synthesis an orthoester reacts with a Grignard reagent to form an aldehyde; this is an example of a formylation reaction.
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