The reactions of malonyl chloride with isocyanates and phenylisothiocyanate were reinvestigated. The products were proved to be N-substituted 7-chloro-2,3- dihydro-21 4,5-trioxo-pyrano(3,4-e)-(1,3)-oxazines. The substituent at position 3 depended on the isocyanate. In the case of phenylisothiocyanate, the product was 7-chloro-2,3-dihydro-40-dioxo-3-phenyl-2-thiopyrano (3,4-e)- (1,3)-oxazine. 'The structures of these products were elucidated by partial synthesis from 6-chloro-4-hydroxy- oxopyran-3-earbonylehloride and by degradation. The chloro-products were degraded with alcohols to derivatives of 2,3-dihydro-2.,4-dioxo-1,3-oxazine and then to amides of acetone-1,1,3-tricarbethoxylate, which gave crystalline copper enolates. The structure of the amides was supported by the infra-red and nuclear magnetic resonance spectra. Similarly, the chloro-products were reacted with secondary and primary amines to form substituted amino-pyrano oxazines and thence diamidoderivatives of dihydro-dioxo-1,3-oxazine. One of the latter compounds was further degraded to give an acetonetricarboxy amide in which the amide groupings were all different. Support Support for the structures assigned to the amine products was obtained from the u.v., infrared and the proton magnetic resonance spectra. Two novel methods of forming N-substituted dihydroxypyridones were discovered and their general nature was established. One route was the oyolisation of mono amides of acetone-1,1,3-tricarbethoxylate: the other was from dialkyl ester deriiratives of 2,3-dihydro-2,4-dioxo-1,3-oxazine. The structures of the pyridones were confirmed by spectroscopy and by degradation. For instance, 5-ethoxycaibony1-4,6-dihydroxyl- pheny1-2-pyridone was transformed to the known compound, N-phenyl-2-piperidone. The synthesis of 5-ethoxycarbony1-416-dihydroxy-lpheny1- 2-pyridone from 7-anilino-2,2-dimethy1-2,4- dioxopyrano(41 3-d)-(113)-dioxin illustrated the use of another acetone-tricarboxylic precursor. A number of amino and methoxy derivatives of acetone-tricarbethoxylate was also cyclised to the corresponding pyridones. The reactions of malonyl chloride with enolic 1,3- diketones yielded 5,6-substituted 4-hydroxy-2-oxopyrans. The constitution of the latter was established by transforming them into known compounds. The behaviour of these pyrones towards amines was also studied. The nuclear magnetic resonance of these compounds showed that they existed in the mono enol-form rather than the, diketone form usually employed to represent them.