2-Substituted 1,3-Benzoxathiolium Tetrafluoroborates as Efficient Acylating Agents for N,N-Dialkylarylamines

2-Substituted 1,3-benzoxathiolium tetrafluoroborates were used as efficient masked acylating agents for N,N-dialkylarylamines in a two-step reaction. In most of the cases intermediate 2,2-disubstituted 1,3-benzoxathioles were obtained in high yields (about 90%) and their hydrolysis afforded the corresponding ketones in almost quantitative yields. The new procedure offers the following advantages: (1) the reaction conditions are mild; (2) the acylation proceeds selectively at the para-position as referred to the dialkylamino group; (3) the introduction of a tertiary group is easily accomplished.