Ketene Thioacetals in Furan Ring Construction

Significance

A sequence starting via thiomethylation of a ketene S,S-acetal, containing an electron-withdrawing group followed by regioselective oxidation and [3+2] annulation constitutes a new trisubstituted furan synthesis. The yields in the ­allylic sulfoxide synthesis were generally high and the annulation proceeded in poor to good yields. The furans can be further converted into 2-aminofurans in almost quantitative yields by a nucleophilic substitution reaction. Substrate scope was quite well studied. A mechanism without evidence was proposed.