A series of 6-methoxy-or siloxy-4H-1, 3-dioxin-4-ones was synthesized from Meldrum's acids. These dioxinones underwent 4+ 2 cycloreversion to methoxy-or siloxycarbonylketenes and ketones quantitatively at 20–50° C. The ketenes were characterized by IR spectroscopy as well as by trapping with t-butanol. The ready cycloreversion of these enolized Meldrum's acid derivatives strongly indicates that the ...