Benzoxathiolium Salts

Benzoxathiolium salts have proven to be effective masked acylating agents (79S223). 2-Substituted 1,3-benzoxathiolium tetrafluoroborates have now been utilized in the preparation of esters. Reaction of the salt (334) with two equivalents of an alcohol gave the 2-alkoxy-2-alkyl-benzoxathiole (335). Hydrolysis of (335) with red mercury(II) oxide and boron trifluoride etherate in aqueous THF delivered ethyl benzoate in excellent yield (Scheme 72). 

Phosphorus oxide chloride 1,3-Benzoxathiolium salts from carboxylic acids and o-mercaptophenols... 

Esterification.—Another way to improve the sometimes unsatisfactory N,N-dicyclohexylcarbodi-imide esterification method is to add catalytic quantities of toluene-p-sulphonic acid to the reaction mixture (c/. 3, 149). Esters can be obtained very rapidly and generally in high yields by reactions between 2-substituted 1,3-benzoxathiolium salts and alcohols (Scheme 30). One drawback could be the rather acidic conditions employed in the second step. A neat modification of the mixed-anhydride esterification method requires no added acid or base in the final step but uses an intramolecular cyclization as the driving... 

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