When 5-hydroxypyrazolidines reacted with ketones on the surface of basic adsorbents the 3-regioisomers were obtained in addition to the expected 5-oxoalkylpyrazolidines. The conditions for the regiodirection of the process have been found.Keywords: ketones, 3-and 5-oxoalkylpyrazolidines, diastereoselectivity, isomerization, mass spectroscopic analysis of isomers, reactions on the surface of adsorbents.We have shown earlier [1] that 5-hydroxypyrazolidines 1a,b react with CH-acids on the surface of alumina without solvent at 60°C to give the corresponding 5-functional derivatives of the pyrazolidine series; in particular, compound 1a reacted with a number of ketones. The hydroxypyrazolidine 1b, which has a transmethyl group in position 3, does not react with ketones for steric reasons -replacement of the hydroxy group in compound 1b requires more vigorous conditions than for compound 1a [1]. We recently reported [2] that hydroxypyrazolidines 1a,b reacted with acetophenone on a potassium fluoride surface deposited on aluminum oxide (at 80°C) or barium hydroxide (at room temperature) to form mixtures of the regioisomers 3a,b and 5a,b (Table 1).It may be assumed that the reason for the formation of the regioisomers 3 is participation in the reaction of the linear tautomer of hydroxypyrazolidine 1 which readily undergoes "retro-Michael" decomposition to the hydrazide and crotonic aldehyde with subsequent "reverse" addition of the hydrazide to the double bond under conditions of basic catalysis.The regioisomeric hydrazino aldehyde 1b' evidently exists in the linear form only (likes its analog prepared from hydrazobenzene [3]) and reacts directly with acetophenone. In a model experiment on a KF/Al 2 O 3 surface 1-acetyl-2-phenylhydrazine, crotonic aldehyde, and acetophenone were deposited on the surface and subjected to the conditions used for the reacion with hydroxypyrazolidine [2]. As a result the regioisomers 3 and 5 were obtained in close to the same ratio as in the normal reaction which serves as additional support in favor of the proposed scheme for the process. __________________________________________________________________________________________ 1 M.
