G. Reddy, K. Rao, M. Khalilullah
2005
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Journal
Heterocyclic Communications
Abstract
A series of 2-aryl-4-(l,3-diarylpyrazol-4-yl)benzopyrano[4,3-0]pyridines (6a-h) have been synthesized. Introduction The pharmacological properties associated with benzopyrans has created interest in the synthesis of benzopyrano fused heterocycles. Thus several benzopyrano pyridines with anti allergic activities have been reported. Recently this class of compounds have also been reported useful in the treatment of diabetes impaired glaucoma tolerance, ulcerative colitis, Crohn's disease, hypertension and obesity disorders. Furthermore, several pyrazoles are known for their biological activities such as antianxiety, antipyretic, analgesic and antiinflammatory. Previous publications from these laboratories^has described the synthesis of several benzopyranopyridines substituted with interesting pharmacophores like coumarins, chromones and benzoxazines. In continuation of our work on pyrazoles, we report herein the synthesis of some new benzopyranopyridines substituted with pyrazoles. α,β-Unsaturated ketones are useful intermediates for the synthesis of a variety of heterocyclic compounds. Exocyclic α,β-enones in which carbonyl group forms part of the ring system are also useful for the synthesis of various polycyclic ring systems. In the present work, the exocyclic α,β-unsaturated ketone system (3) is obtained by the condensation of 2,3-dihydro-4H-benzopyran-4-one (1) with substituted 1,3-diarylpyrazole-4carboxaldehydes 2 in the presence of sodium methoxide in refluxing methanol. 3 Underwent smooth cyclocondensation with phenacyl pyridinim bromides 4 in the presence of ammoniumacetate in refluxing acetic acid to give the desired 4-pyrazolyl benzopyrano pyridines 6 in good yields (Scheme-1). The formation of 5 is evident by the absence of carbonyl function in IR spectra and the shift o f -OCH2 signal from δ 5.22 present in 3 to δ 4.82 ppm in the cyclic system in the 'H NMR spectra of 6 apart from the other aromatic, Vol. 11, Nos. 3-4, 2005 Synthesis of 2-aryl-4-( 1,3-diaiylpyrazol-4-yl)-benzopyrano[4,3b]pyridines pyrazole and pyridine protons. All the compounds reported in Table 1 were characterized by their correct IR, 'H NMR, Mass and elemental analyses. .Ri R n r S N 0 ο 4 Br