3-Pyrazolidinones structure

Dimethyl acetylenedicarboxylate with several pyrazolidinones (142 R1, R2, R3 = H or alkyl) gives131 the normal Michael adducts 143 and the diazepinones 144 the crystal structure was determined for one diazepinone. 

Pyrazolinones and pyrazolidinones are oxo derivatives of pyrazo-lines and pyrazolidines, respectively, and are so named in Chemical Abstracts at present. However, the usual method of naming in the earlier literature is the pyrazolone-pyrazolidone system. Although a large number of tautomeric structures are possible for pyrazolinones, the usual assignment of ring structures is as shown in (I), (II) and (III). The Chemical Abstracts names for these are (I) 2-pyrazolin-5-one, (II)... 

The pyrazolidinones (IV) present a number of possibilities for structural isomerism, but very little study of their structure has been made. It is generally assumed that they have the classical form (IV). 

Ultraviolet and infrared spectra have been considered in some detail in the section dealing with structure. Concerning the ultraviolet spectra it can be stated that, while there is considerable absorption by pryazolinones and some pyrazolidinones, these absorptions are so complex, owing to tautomerism, that little can be deduced from them. 

A most unusual photochemical oxidation occurred on 5-methyl-2-phenyl-3-pyrazolidinone (158) in acetone to give the spiroepoxide product (159). The structure of the epoxide (159) was confirmed by MCPBA epoxidation of the olefin (160). The oxidation of salicyl alcohol with sodium periodate... 

Gould E, Lebl T, Slawin AMZ, Reid M, Smith AD. Structural effects in pyrazolidinone-mediated organocatal34ic Diels-Alder reactions. Tetrahedron 2010 66 8992-9008. 

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