Ahmad S. Shawali

Cycloaddition of diphenylnitrilimine to coumarins. The synthesis of 3a, 9b-dihydro-4-oxo-1H-benzopyrano [4,3-c]pyrazole derivatives

Abstract The cycloaddition of diphenylnitrilimine to a series of coumarins occurs with the same regioselectivity in all cases, regardless the nature of the substituent present, to yield the corresponding 3a,9b-dihydro-4-oxo-lH-benzopyrano [4,3-c]pyrazoles 4 a–f. Dehydrogenation of 4a yields 4-oxo-1H-benzopyrano [4,3-c]-pyrazole 6 . In ethanolic sodium ethoxide solution, the reaction between coumarin and diphenylnitrilimine precursor, namely N-phenylbenzohydrazidoyl chloride 1 , affords no cycloadducts, but yields o-(β-ethoxycarbonylvinyl)phenyl N-phenylbenzohydrazidate 10 . The regiochemistry of the cycloadducts 4 a–f and the reaction sequence leading to 10 are outlined. The structures of the products have been established by spectroscopic methods and independent syntheses wherever possible.

Regioselectivity in the reactions of diphenylnitrilimine with coumarin and chromone

Abstract The cycloaddition of diphenylnitrilimine with coumarin and chromone gave the cycloadducts 4 and 5 respectively. The structures of these products were based on elemental and spectral analyses and alternate synthesis. The orientations of the cycloaddition are interpreted in terms of FMO theory.

The structure of the cycloaddition products of α-ketonitrilimines to α, β-unsaturated ketones

Abstract The cycloaddition of C-ethoxycarbonyl-N-aryl-nitrilimines 3 and their C-acetyl analogs 4 to α,β-un-saturated ketones 5 give predominantly the 5-acyl-4-aryl-2-pyrazoline derivatives 8 and 9 respectively. The structures of the cycloadducts 8 and 9 were supported by spectral (13C NMR, 1H NMR and IR) and analytical data. Tewari and Parihars conclusions about the regiochemistry of these reactions cannot be sustained.

Structure and acidity of some heterocyclic nitrosazones

Several new heterocyclic nitrosazones were prepared and their acid dissociation constants determined in 50 volume percent ethanol-water solution at 25.0 ± 0.1° and μ of 0.10. Infrared, electronic, and pmr spectra of these compounds and some deuterated nitrosazones were also examined and compared with their O-methyl derivatives. It is concluded that all compounds have the azo oxime structure and that the stereochemistry around the azo group is trans. The data revealed also that the nitrosazones derived from pyridine aldehydes show the existence of equilibria between zwitterionic and neutral molecules. No evidence for the tautomeric nitroso-hydrazone form could be obtained.

Synthesis of some new 2-imino-2,3-dihydro-1,3,4-thiadiazole and selenadiazole derivatives

(2) Diazotized 3(5)amino-5(3)-phenylpyrazole reacts with phenacylthiocyanate (1) and phenacylselenocyanate (10) to give the corresponding 1,3,4-thiadiazoline derivative (5) and 1,3,4- selenadiazoline derivative (12), respectively. A mechanism is proposed and it is substantiated by an alternate synthesis of 5 and 12 from the corresponding hydrazidoyl bromide (6) with potassium thiocyanate and potassium selenocyanate, respectively. The thiadiazoline (5) and selenadiazoline (12) give the respective N-acyl derivatives (7a) and (12) with acetic anhydride. Nitrosation of 5 and 12 gives the corresponding N-nitroso-derivatives (8a) and (14), respectively. Cyclization of 6 gives the corresponding 9 with triethylamine in benzene.