Enamines typical reactivity

The typical reactivity of an enamine 1 results from the nucleophilic character of the /3-carbon center, as indicated by a resonance structure ... 

Most 77-bond nucleophiles (enols, enol ethers, enamines, as well as simple alkyl-substituted alkenes and arenes) can exist under either acidic or basic conditions, but enolates exist only under basic conditions. Among 7r-bond nucleophiles, however, only enolates and enamines are reactive enough to attack the electrophiles typically seen under basic conditions. 

Some enamine alkylation reactions are shown in Scheme 1.10. Entries 1 and 2 are typical alkylations using reactive halides. In Entries 3 and 4, the halides are secondary with a-carbonyl substituents. Entry 5 involves an unactivated primary bromide and the yield is modest. The reaction in Entry 6 involves introduction of two groups. This... 

Alkylation of enamines requires relatively reactive alkylating agents for good results. Methyl iodide, allylic and benzylic halides, a-haloesters, a-haloethers, and a-haloketones are the most successful alkylating agents. Some typical examples of enamine alkylation reactions are shown in Scheme 1.10. 

The reactivity of the produced complexes was also examined [30a,b]. Since the benzopyranylidene complex 106 has an electron-deficient diene moiety due to the strong electron-withdrawing nature of W(CO)5 group, 106 is expected to undergo inverse electron-demand Diels-Alder reaction with electron-rich alkenes. In fact, naphthalenes 116 variously substituted at the 1-, 2-, and 3-positions were prepared by the reaction of benzopyranylidene complexes 106 and typical electron-rich alkenes such as vinyl ethers, ketene acetals, and enamines through the Diels-Alder adducts 115, which simultaneously eliminated W(CO)6 and an alcohol or an amine at rt (Scheme 5.35). 

The anhydro bases, e.g. (61), formed by deprotonation of 2- and 4-alkylquinolinium salts, are more stable than the pyridone methides and are usually isolable. They are reactive enamines and some typical chemistry is shown in Scheme 50. 

Although the reactivity of enaminones is not always the same as that of typical enamines due to the additional conjugative interaction with the carbonyl group, the anodic oxidation of enaminones seems useful in organic synthesis since they yield dimerized or cyclized products upon anodic oxidation. In anodic oxidation of the enaminones or enaminoesters in methanol containing sodium perchlorate, for instance, derivatives of pyrrole are formed via initial dimerization (equation 4)5. 

Although the nucleophilic reactivity is generally less than that of the enamine, one of the typical reactions of the enecarbamates and enamides is the reaction with electrophiles at the -position (equation 8). Since this review deals with electrochemistry, chemical reactions of enecarbamates and enamides are not included but some of them are summarized elsewhere9. The oxidation potentials of enecarbamates are more positive than those of enamines (EJV vs SCE, 7 = 1.59 V 8 = 1.37 V in CH3CN-0.1N LiC104, 100 mV/s). 

Enamines are an important class of uncharged synthetic intermediates that exhibit carbanion-like reactivity. They are typically prepared from ketones with one or more a-hydrogens and a secondary amine under acid catalysis ... 

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