Tautomerism hydroxyimine-amide

Tautomerization of the hydroxyimine yields an amide in a reaction analgous to the tautomerization of an enol to give a ketone. 

Lactams Lactams represent a special type of C=N system due to the tautomerization between the lactam (keto amine) and lactim (hydroxyimine) forms. The lactim form is much more favored for cyclic than for non-cyclic amides of carbocyclic acids. In the reaction of complex 2b with N-methyl-e-caprolactam, a simple ligand exchange reaction occurs and complex 87 can be isolated. With P-propiolactam, the alkenyl-amido complex 88 is formed, which indicates an agostic interaction. The reaction of complex 1 with e-caprolactam gives, after elimination of the alkyne and of molecular hydrogen, complex 89 with a deproto-nated lactam in a r]2-amidate bonding fashion [47]. 

In addition, detailed geometric and energetic characteristics of the elementary reaction pathways for the addition of water and ammonia to 2-methyl-5(477)-oxazolone have been determined at the AMI level using MOPAC programs. The authors concluded that an A-acetylamino acid or amide are formed through a two-step procedure that involves the formation of the a-hydroxyimine and subsequent tautomerization. 

The metal-promoted reactions with nucleophiles generally yield metal complexes of the intermediate imino species and it is quite unusual to observe the carboxylate products derived from the attack of a second equivalent of nucleophile. A wide variety of products have been observed. The ligands may be monodentate O- or A-bonded species, or exhibit a didentate N,0-mode. The ligands may be in the amide or the hydroxyimine tautomeric forms, and may be neutral or deprotonated (Fig. 4-8). 

The intramolecular Diels-Alder reactions of simple, 4-hydroxy- or 4-alkyl-6-oxopyrimidines80,81 bearing olefinic, acetylenic, or nitrile dienophiles have been investigated (Table 10-VI). In many instances, the initial intramolecular pyrimidine Diels-Alder products are thermally stable due to the formation of a bicyclic amide. The elimination of cyanic acid (HNCO) apparently requires thermal tautomerization of the amide to the hydroxyimine and subsequent retro-Diels-Alder reaction. The application of these observations in the total synthesis of ( )-acetinidine has been detailed [Eqs. (20) and (21).82... 

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