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Chapter-5<br />

Synthesis of highly substituted pyrroles<br />

Figure-18<br />

In continuation with this study prior work at <strong>Saurashtra</strong> <strong>University</strong> on 1Hpyrrole<br />

derrivatives clubed with substituted-1,3,4-Oxadiazoles, 1-[2,4-dimethyl-5-(5-<br />

phenyl-1,3,4-oxadiazol-2-yl)-1H-pyrrol-3-yl]ethanone derivatives were synthesized.<br />

The synthetic stretagy follows starting with acid catalyzed cyclocondensation of ethyl<br />

ester derivative of 3-amino-2-butenoic acid (generated insitu from ethylacetoacetate<br />

upon oximenation followed by reduction) with acetylacetone to afford ethyl-3-acetyl-<br />

2,4-dimethyl-1H-pyrrole-5-carboxylate, which was derivatized into corresponding<br />

hydrazide derivative on treatment with hydrazine hydrate. The hydrazide derivative<br />

on reaction with different aromatic and heteroaromatic acid, in the presence of<br />

phosphorous oxychloride affords 1-[2,4-dimethyl-5-(5-phenyl-1,3,4-oxadiazol-2-yl)-<br />

1H-pyrrol-3-yl]ethanone derivatives (Figure-19). 35-36<br />

Figure-19<br />

A range of 2,5-disubstituted and 2,4,5-trisubstituted pyrroles can be<br />

synthesized from dienyl azides at room temperature using ZnI 2 or Rh 2 (O 2 CC 3 F 7 ) 4 as<br />

catalysts (Figure-20). 37<br />

Figure-20<br />

The CuI/N,N-dimethylglycine-catalyzed reaction of amines with γ-bromosubstituted<br />

γ,δ-unsaturated ketones in the presence of K 3 PO 4 and NH 4 OAc gave the<br />

corresponding polysubstituted pyrroles in very good yields (Figure-20). 38<br />

Department of Chemistry, <strong>Saurashtra</strong> <strong>University</strong>, Rajkot-360005 164

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