Esterification Trimethyl orthoformate

Conversion of (107) into the dimethyl acetal (108) with trimethyl orthoformate and Rexyn 101, followed by pyrolytic elimination in refluxing o-xylene, gave (109). Treatment of (109) with n-butyl-lithium and C02 in THF, followed by hydrolysis, afforded the keto-acid (110). Reduction of (110) with borohydride, followed by dehydration with phosphoric acid and esterification, gave (111). 

Fig. 9.15. Gentle esterification of a carboxylic acid I with trimethyl orthoformate (upper part). The lower part gives an example of a chemoselective esterification according to the procedure discussed.

Esterification of sulfonic acids.1 Sulfonic acids are converted into methyl or ethyl esters on reaction with trimethyl or triethyl orthoformate. Yields are >80% in esterification of arenesulfonic acids, but are somewhat lower in the reaction of alkanesulfonic acids because of volatility of the products. 

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