Studies of the reactions of the dione 3 and lactone 4 dimers of dimethylketene with a series of trialkyl phosphites and with dimethyl methylphosphonite have been carried out. The reactions of 4 give generally a carboalkoxy enol phosphite 9, whereas the dione 3 reactions yield either 9 or a carboalkoxyl oxophosphonite 8 depending on the phosphite used. ... Tri-n-butylphosphine effects the isomerization of 3 to 4. ... Simple unsubstituted dialkyl and diary1 ketones are ...