Reaction of cross-conjugated dienones with phenyl-and 2-pyridylhydrazines

Abstract

New pyrazoline derivatives were synthesized by condensation of dienones based on cyclo hexanone and N substituted piperidin 4 ones with phenylhydrazine and 2 pyridylhydrazine. The reaction with phenylhydrazine produces trans isomers. , 2 R 3 aryl 7 [(E) aryl methylene] 3,3a,4,5,6,7 hexahydro 2H indazoles, 5 R 3 aryl 7 [(E) arylmethylene] 2 phe nyl 3,3a,4,5,6,7 hexahydro 2H pyrazolo[4,3 c] pyridines.The ability of α,β unsaturated derivatives of cyclic ketones to add binucleophiles is widely used in organic synthesis. Due to the presence of the cross conjugated dienone system, α,β dienones are involved in hetero cyclization reactions with nucleophilic reagents, such as urea, 1,2 thiourea, 3-9 cyanoacetamide, 3,9,10 and malono nitrile. 11,12 The reactions of various mono and dienones based on cyclic ketones with guanidine and its alkyl de rivatives were studied. 13,14 The reactions of unsubstituted hydrazine with mono and dienones produced pyrazoline derivatives. 15-17 There is evidence for the possibility of performing analogous reactions with hydrazine deriva tives RNH-NH 2 , where R are aliphatic 3,7,18,19,20 or aro matic 3,4,17,21,22 substituents.In the last fifteen years, the chemistry of coordination polymers, which are infinite assemblies of metal ions and exo dentate ligands, has attracted great interest. These structures were extensively studied as catalytic, lumine scent, magnetic, and porous materials. 23 Recently, 24 we have proposed symmetrical cross conjugated dienones containing pyridyl substituents for the use as exo dentate ligands. Additional substituents, which are able to be co ordinated to metal atoms, can be introduced into dienone structures by heterocyclization. This leads to changes in the dentation and directionality of the donor pairs of the ligand, which can influence the complexation and prop erties of the resulting supramolecular structures. In this connection, the aim of the present study was to synthesize pyrazoline derivatives containing pyridyl substituents in the dienone and/or arylhydrazine components. The goal was also to characterize the structures and stereochemis try of the products in detail.Cyclic ketones 1 were used to prepare dienone sub strates 2a-k according to known procedures. 25, 26 We syn thesized a series of new bicyclic pyrazolines 3a-c and 3e-i by heterocyclization of dienone derivatives of cyclic ketones with phenylhydrazine (Scheme 1). Compound 3d has been characterized earlier. 3 However, its structure has not been established by spectroscopic methods. Only the melting point, the molecular ion, and elemental analysis data were documented. 3 Heterocyclization was carried out in ethanol with the use of a fourfold excess of phenyl hydrazine. 17

An efficient and stereoselective synthesis of pyrazolo[4,3‐c]pyridine derivatives under microwave heating

“…100 12 64 2 HOAc 100 16 35 3 EtOH 100 14 58 4 None 100 12 47 5 DMF 100 16 55 6 Glycol 90 16 61 7 Glycol 110 10 81 8 Glycol 120 8 89 9 Glycol 130 8 85 10 Glycol 140 8 88 Table 2 The reaction times, melting points, and yields of products. [14] 92 (42) [14] a Isolated yields under microwave heating conditions.…”

“…The pyrazolo[4, 3-c]pyridine derivatives were, previously, mostly synthesized through the reaction of a,bunsaturated ketones with substituted hydrazine in different reaction conditions such as (i) catalyzed by NaOEt in HOEt for 10 h [12], (ii) in refluxing MeOH for 4 h [13], (iii) in refluxing EtOH for 6 h [14], and (iv) catalyzed by Et 3 N in refluxing EtOH [15]. However, the continued development of a facile and versatile method to pyrazolo[4, 3-c]pyridine derivatives is still desired.…”

Lewis Acids as Mild and Effective Catalysts for the Synthesis of 3,5‐Bis[(hetero)arylidene]piperidin‐4‐ones

“…The structures of the known 3,5-bis[(hetero)arylidene]piperidin-4-ones 2a [18], 2c [19], 2e [20], 2f [21], and 3a [22] obtained via Methods A and B as free bases were confirmed by the multinuclear NMR spectra. Their physicochemical constants fit well the available literature data.…”

Novel Linear Bis-Crown Receptors with Cross-Conjugated and Conjugated Central Cores

“…Cross-conjugated dienones -derivatives of cyclic ketones [12] -attract the attention of researchers due to their rich synthetic chemistry, primarily for the production of heterocycles, [13][14][15] and wide opportunities for application, especially in biology, agriculture and the creation of new materials. [16][17][18][19][20][21][22] Recently, cross-conjugated dienones with pyridine substituents have been used as ligands to produce discrete and polymeric coordination compounds.…”