Som N. Dhawan

Synthesis and anti-inflammatory evaluation of some pyrazolo[3,4-b]pyridines

Novel series of pyrazolo[3,4-b]pyridines with basic skeleton different from the known COX inhibitors were synthesized from 5-amino-1-[4-(aminosulfonyl)phenyl]-3-phenyl-1H-pyrazole, which in turn was prepared by the condensation of (4-sulfamoylphenyl)hydrazine with α-cyanoacetophenone. All the newly synthesized compounds were tested for their in vivo anti-inflammatory activity by carrageenan-induced rat paw edema assay. Some of the most potent compounds were evaluated in different COX and LOX assays. Some of the new compounds were found to possess moderate anti-inflammatory activity.

On the mechanism for the phototransformation of 3-alkoxy-2-(2′-furyl)-4-oxo-4H-1-benzopyrans

Photoirradiation of 3-alkoxy-6-chloro-2-(2′-furyl)-4-oxo-4H-1-benzopyrans 3 led to the formation of methyl 8-chloro-10-oxo-2-phenyl-2,3,4,10-tetrahydropyrano[3,2-b][1]benzopyran-3-ylacetate 4. The reaction proceeds through the formation of 8-chloro-4-phenyl-3a,4,6,11b-tetrahydrofuro-[2′,3′:4,5]pyrano[3,2-b]benzopyran-6-one 5a, which subsequently undergoes a ring contraction–ring expansion mechanism to give the cyclopropanecarbaldehyde 8 followed by its rearrangement to ketene 10via the carbene 9 to furnish ester 4. The various intermediates have been isolated and identified, and their stereochemistry was established from their 1H NMR spectra.

Stereoselective synthesis of Z-3-alkoxy-2-[(4′-methoxyphenyl)methylidene]-1(3H)-isobenzofuranones

Abstract Photoreorganisation of 2-alkoxy-2-(4′-methoxyphenyl)-1H-indene-1,3(2H)-diones in anhydrous acetone affords exclusively Z-3-alkoxy-3-[(4′-methoxyphenyl)methylidene]-1(3H)-isobenzofuranones. The products were identified by X-ray crystallography of one of them.

Photoreorganisation of some bischromones

Abstract Photoreorganisation of 2,2′-dithienyl/diphenyl-3,3′-polymethylene-dioxychromones is described. The product formation has been found to depend upon the length of the intervening alkyl chain.

Vilsmeier-haack reaction on hydrazones : a convenient synthesis of 4-formylpyrazoles

Vilsmeier–Haack reaction has been found to be an excellent method for the formylation of a variety of hydrazones to yield the corresponding 4-formylpyrazoles.

Synthesis and characterisation of some novel indeno[1,2-c]pyrazoles

1-(Benzothiazol-2-yl)-4-phenylindeno [1,2-c]pyrazoles (1) and 1-(4-arylthiazol-2-yl)-4-phenylindeno[1,2-c]pyrazoles (2) have been synthesised by the reaction between 1-oxo-3-phenylindan-2-carboxaldehyde (4) and 2-hydrazinobenzothiazoles or 2-hydrazinothiazoles.

Photochemistry of chromones: photoreorganisation of 3-alkoxy-2-thienyl-4-oxo-4H-1-benzopyrans

Photoirradiation of a methanolic solution of 3-alkoxy-2-thienyl-4-oxo-4H-1-benzopyrans with Pyrex filtered UV light leads to cyclised and cyclodehydrogenated angular products involving both thiophene and alkoxy groups. The reaction is initiated through H-abstraction. The product distribution depends upon the substituents on the thiophene ring.

Photocyclisation of 3-alkoxythiochromones: activation for H-abstraction

Photocyclisation of 3-alkoxy-2-arylthiochromones leads to angular tetracyclic compounds through H-abstraction that requires activation by a phenyl group.

Phototransformation of some N -(2-hydroxy-1,3-dioxo-2,3-dihydro-1 H -inden-2-yl)aryl/heterylamides

Photoreorganisation of few N-(2-hydroxy-1,3-dioxo-2,3-dihydro-1H-inden-2-yl)aryl/heterylamides 1 to N-benzoyl-3-oxo-1,3-dihydro-2-benzofuran-1-carboxamides 2 is described