Download (3100Kb) - Etheses - Saurashtra University

(5) Iodobenzene diacetate, a relatively nonmetallic oxidant, has been utilizedefficiently for the oxidation of N-substituted hydrazones of chalcones toafford 1,3,5- trisubstituted pyrazoles under mild reaction conditions. 397REACTION MECHANISM :The following mechanism seems for the condensation of chalcones withhydrazine hydrate.OR R 1(I)NH R 2H 2 NCH -H CH -H C3 CCH3 CH 33Proton RR 2O 2 transferN +OHN +NHNH 2H 2H(II)RNNR 2R 1RHONH(IV)NR 1R 2RR 1O NR 2 NH 2(III)Nucleophillic attack by hydrazine at the β–carbon of the α,β–unsaturatedcarbonyl system forms species (II), in which the negative charge is mainlyaccommodated by the electronegative oxygen atom. Proton transfer from nitrogen tooxygen produces an intermediate and which simultaneously ketonises to ketoamine(III). Another intramolecular Nucleophillic attack by the primary amino group ofketoamine on its carbonyl carbon followed by proton transfer from nitrogen tooxygen lead ultimately to hydroxyl amine (IV). The later with a hydroxyl group andamine group on the same carbon lose water easily to yield the pyrazolines.119Pyrazoline…..