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Part-IISynthesis of Pyrimidineselectron withdrawing group X (Cl) further makes the nitrile C’ more electrophilic orenhances its electrophilicity.Rδ+ δ−NVsδ++δ−NHRClThe imidoyl halide when is reacted with the o-aminocarbonyl substrate, attracts theelectrons of the nucleophilic-NH 2 group of the substrate very readily as follows (Scheme2).Step-1YYNH 2X+ClNHR-HClNHXNStep-2RYYZXNXNNNHRNHRZ= OH, NH 2 , R, H etc;NRY= COOH, COOR', CONHR', CHO, COR', CNXScheme 2The reaction of a nitrile with an o-aminocarbonyl substrate possessing electrophilic andnucleophilic centers leads to the formation of an azaheterocycle through the incorporationof CN of the nitrile in the ring. The mechanism may be any one of the following three, aconcerted cycloaddition process (Type A) or by discreet steps, involving either the initialelectrophilic attack on the nitrile nitrogen (Type B) or by the initial electrophilic attack atthe nitrile carbon (Type C), followed by ring closure 22 (Scheme 3).224