Enamine is formed between ketone and secondary amine in the presence of acid catalyst. [VISUAL] (1) — Organic Chemistry Chemistry Question
Enamine chemistry (Organic synthesis – 3)
Enamine is formed between ketone and secondary amine in the presence of acid catalyst.
[VISUAL] (1)
Propose a mechanism for enamine formation in the presence of acid catalyst (eq. 1).
Model Answer
[VISUAL]
This process exhibits a bell–shaped pH dependence in the presence of acid catalyst. The maximum rate of formation occurs at pH 3–4. Propose a plausible reason why this dependence occurs.
Model Answer
Normally, acid catalyzes the enamine formation as shown in 21.1. However, if too much acid is present, the basic amine (nucleophile) is completely protonated so the initial nucleophilic addition step cannot occur.
Enamine reacts with conjugated enones such as methylvinylketone to form a 1,5– dicarbonyl compound after the hydrolysis of enamine (equation 2).
[VISUAL] (2)
The product of this reaction now has one chiral center. Suggest conditions of special amine to make stereospecific product as shown in equation 2.
Model Answer
An enamine prepared from a single enantiomer of the chiral secondary amine is chiral, and thus the Michael addition reaction can proceed from only one side of enamine to yield a single enantiomeric product.