Pyrazinones acylation

A similar reaction of vincinal aromatic or heterocyclic diamines 104 with 2-benzoylamino-3-chloropropenoic acid 102 resulted in sprro-2-oxazolines fused to a pyrazinone nucleus 108. It is believed that the enamide 102 first isomerizes to the A-acyl imine 103 followed by Michael addition of the diamine 104. The resulting Michael adduct 105 cyclizes to 106 or 107 either of which leads to the same oxazoline 108. Single-crystal X-ray confirmed the structure of 108. Unsymmetrical diamines gave two isomeric products with the predominant product... 

Note In the foregoing syntheses, acyl halides react at their halogeno entity to afford pyrazinones however, sometimes they appear to react at their carbonyl entity (at least with primary amino cosynthons) to afford halogenopyrazines (see examples later in this subsection). 

Uni like alkylation, acylation of 2(l//)-pyrazinones usually occurs exclusively at oxygen to afford an acyloxy derivative only occasionally is an /V-acylpyrazi-none formed. The following examples will indicate the conditions, facility, and yields to be expected of such reactions ... 

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