N-[[(Chlorosulfinyl)oxyl]methylene]-N-methylmethanaminium chloride as A dehydrating agent. A direct and efficient one-pot synthesis of various pyrimidinones, azetidinones and pyridones via cycloaddition reactions

N-[[(Chlorosulfinyl)oxy]methylene]-N-methylmethanaminium chloride (1) is found to be an efficient and mild dehydrating agent for the in situ generation of monophenyl-(4a) diphenyl-(4b) and monochloroketenes (4c) directly from the corresponding carboxylic acids 2. These ketenes undergo cycloaddition reactions with 1,3-diaza-1,3-butadienes 5 to afford 4(3H)-pyrimidinones 6 and azetidones 7, and with 3-(aryliminomethyl)chromones 8 to give [1]benzopyrano[3,2-c]pyridine-3,10[2H]diones 9