.beta.-Keto sulfoxides. VI. Conversion of .omega.-(methylsulfinyl) acetophenone into di- and tri-.omega.-(methylmercapto)-acetophenone. Synthesis of .alpha.-hydroxy aldehydes, .alpha.-keto thio esters, .alpha.-keto esters, .alpha.-hydroxy thio esters, and .alpha.-hydroxy esters. Chemistry of .alpha.-keto mercaptals