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Stereoselective synthesis of /ra/is,/ra«s-2,3,3a,4-tetrahydro-3-aryl-2,4diphenyl[l]benzopyrano[4,3-c]pyrazoles 13-24 have been performed by the reaction of E-3aryhdeneflavanones 1-12 with Phenylhydrazine in hot pyridine. Structures of these new tricyclic pyrazolines have been elucidated by ER, 'Ηand C-NMR spectroscopies. Introduction 3-Arylideneflavanones (termed flavindogenides) are well known flavanone derivatives which can be synthesized by the reaction of flavanones and aromatic aldehydes. For this purpose, an acidcatalyzed condensation was used for a long time (1-6). However, this procedure afforded the target compounds contaminated with the starting flavanones in many cases. For this reason, we have developed a new method for the synthesis of £-3-arylideneflavanones by the piperidine-catalyzed reaction of flavanone with aromatic aldehydes (7,8). These £-isomers can then be photocatalytically isomerized into Z-3-arylideneflavanones (6,9). We have also unambiguously elucidated the stereochemistry of both Eand Z-3-arylideneflavanones by NMR spectroscopy (10). The easy availability of both Eand Z-3-arylideneflavanones made possible several chemical transformations. An interesting chemical transformation of the 3-arylideneflavanones is their oxidation to form either 3-aroylflavones (11-13) or 3-a-hydroxybenzylflavones (11,14). Other oxidation reactions provide their epoxides (15-19). Another useful chemical conversion is their base-catalyzed exo-endo double bond migration to obtain the otherwise inaccessible 3-benzylflavones (20). However, the synthesis of nitrogen-containing heterocyclic compounds starting from 3-arylideneflavanones has hitherto received less attention (21). 151 Unauthenticated Download Date | 6/28/19 10:26 PM Vol. 5, No. 2, 1999 Fused heterocycles 9, synthesis of tricyclic pyrazolines by the reaction of E-3-arylideneflavanones with Phenylhydrazine Results and Discussion Pyrazolines have been prepared from 3-arylideneflavanones both by their reaction with diazomediane (21-23) and with hydrazine derivatives (24,25). Since the reaction with hydrazines were restricted only to diose 3-benzylideneflavanones which bear an unsubstituted phenyhnediylene unit, it seemed expedient to prolong tliis reaction to 3-arylideneflavanones possessing either a substituted phenylmethylene or an arylmethylene group to investigate the influence of the substituent or die space demand of die aryl group. Synthesis of tricyclic pyrazolines by the reaction of exocychc α,β-unsaturated ketones with hydrazines has been studied by several research groups (24-26). This reaction provides tricyclic pyrazolines with two new centres of chirahty which gives rise to the formation of diastereomeric mixtures of pyrazolines. Since the 3-arylideneflavanones have a centre of chirahty, tricyclic pyrazolines obtained from them possess three centres of chirahty which theoretically may result in the formation of four diastereomeric structures rendering the stereochemical outcome of the reaction even more complex. Acid-catalyzed reaction of exocychc α,β-unsaturated ketones with hydrazines (28,29,31,34) afforded a mixture of cisand trans-3-H,3a-H-distereomers of tricyclic pyrazolines. For this reason, this procedure seems to be inconvenient for the synthesis of tricyclic pyrazolines starting from 3-arylideneflavanones. In our previous studies (24,36) it has been found that the reaction of some exocychc α,β-enones with hydrazines in hot pyridine provided £ratts-3-H,3a-Hdiastereomers of tricyclic pyrazolines as stereohomogeneous products. As a continuation, in our present paper we report on the stereoselective synthesis of tricyclic pyrazolines by the reaction of 3arylideneflavanones 1-12 with Phenylhydrazine. Since we wanted to neglect the influence of the stereoisomerism of the starting materials, in our present study we investigated this reaction only of £'-3-aryhdeneflavanones where the carbonyl group and the aryl moiety are on the opposite sides of the C=C double bond. 3-Arylideneflavanones 1-12 were allowed to react with Phenylhydrazine in hot pyridine to afford tricyclic pyrazolines 13-24 (Scheme 1). Structures of new compounds 13-24 have been elucidated by microanalysis, IR and 'Hand C-NMR spectroscopies (cf. Experimental). In the [R spectra a characteristic C=N band was found at around 1595-1598 cm' referring to the formation of a pyrazoline ring. In the 'H-NMR spectra both the chemical shift values and the multiplicities of the aliphatic protons are in full harmony with the presence of a tricyclic pyrazoline ring system. This is 152 Unauthenticated Download Date | 6/28/19 10:26 PM A. Levai Heterocyclic Communications

FUSED HETEROCYCLES 9, SYNTHESIS OF TRICYCLIC PYRAZOLINES BY THE REACTION OF E-3-ARYLIDENEFLAVANONES WITH PHENYLHYDRAZINE