Tautomerism imine-enamide

The /V-acy 1 imine-enamide tautomerism of methyl 2-acetamidoacrylate has been studied641 by means of ab initio calculations. A 13 C NMR investigation has been undertaken to study the tautomerism between the hydrazone imine and diazenylen-amine forms of 3-(arylhydrazono)methyl-2-oxo-l,2-dihydroquinoxalines,642 and the effects of temperature and side-chain on the imine-enamine tautomerism in quinoxalinone and pyridopyrazinone systems have been studied.643 A detailed... 

Condensation of an amino acid-derived anilide and a /3-ketoamide afforded l,4-benzodiazepin-2-ones in which the initially formed imine tautomerizes to an exocyclic enamide (Scheme SO) <2001TL3227>. Only the (Z)-isomer of the enamide was isolated, assigned based on NOE data, and presumably reflecting stabilization by an intramolecular H-bond between the ring NH and exocyclic amide carbonyl. 

N-Sulfonyl imines derived from enolizable aldehydes and ketones are, in principle, capable of tautomerization to the corresponding ene sulfonamides. There has been no systematic study of this process, probably due in large part to the fact that only relatively few sulfonyl imines of this type have to date been prepared and characterized. Trost and Marrs [17], however, have found that aldehyde 35 on conversion to imine 36 using tellurium reagent 3 led to enamide 37 upon workup (Scheme 9). Similarly, aldehyde 38 was converted to imine 39 which tautomerized to 40 upon isolation. 

In the hypothesized catalytic cycle, in the presence of catalyst and the co-catalyst acetic acid, the enamide 1 is tautomerized to the corresponding imine, which is activated by the acid via an iminium intermediate. In the following step, only chiral phosphoric acid is active enough to catalyze the hydrogenation of the imine, while the acetic acid role is probably only to help keep a sufficient concentration of iminium intermediate present since it was used in such small quantities (Figure 15.7). 

Ruthenium/Br0nsted Acid System The tandem isomerization/Friedel-Crafts reaction of aUylamides reported by Sorimachi and Terada was another early example of a cascade catalysis procedure using Brpnsted acid and metal salts as catalysts (Scheme 2.93) [127]. With the promotion of the ruthenium catalyst 342, the aUylamides isomerized to enamide X32, which was then tautomerized by a Brpnsted acid (343 or 344) to form imine X33 then the electron-enriched aromatic substrates 341 attacked the Brpnsted acid-activated imine intermediates to afford Friedel-Crafts products 345 in up to 91% yield. 

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