Orthoester carboxylic acid protecting group

Carboxylic acids can also be protected as orthoesters. Orthoesters derived from simple alcohols are very easily hydrolyzed, and the 4-methyl-2,6,7-trioxabicyclo[2.2.2]octane structure is a more useful orthoester protecting group. These... 

The rearrangement of isopent-3-enyl epoxy esters with Cp2ZrCl2/AgC104 yields asymmetric bicyclo octane esters which are base-stable protecting groups for carboxylic acids (Scheme 48). However, the orthoesters are only the kinetic products and can rearrange under reaction conditions to more stable THF derivatives. 

When l,l,2-triphenylethane-l,2-diol-derived esters are submitted to a monodeprotonation and subsequently treated with Chlorotrimethylsilane, the formation of 2-trimethylsilyloxy-l,3-dioxolanes results. The orthoester moiety thus obtained serves as a protecting group for carboxylic acids (eq 3) it is stable towards alkyllithium reagents and can be cleaved under nonacidic conditions by alkaline hydrolysis. ... 

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