Orthoacetic acid trimethyl ester

The diflorasone is reacted with orthoacetic acid trimethyl ester in the presence of toluene sulfonic acid to give diflorasone diacetate. 

Trimethyl orthoacetate Orthoacetic acid, trimethyl ester (8) Ethane, 1,1,1-trimethoxy-(9) (1445-45-0)... 

The trivial name acetoxy is retained for the CH3—CO—O— group. Compounds of the type R C(0R )3 are named as R esters of the hypothetical ortho acids. For example, CH3C(OCH3)3 is trimethyl orthoacetate. 

The ribofuranose units have one extra OH group that requires protection. If iV-benzoyl A-ribofuranose (144) is treated with a catalytic amount of p-tolu-enesulfonic acid and trimethyl orthoacetate, (MeOlgC-Me, the C2/-C3 diol unit is converted to an orthoester (in violet an aldehyde is converted to an acetal and an ester is converted to an orthoester), as in 145. An orthoester has the structure RC(OR)g, but this class of compounds will not be discussed further. This compound has the 5 OH free. 

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