Chapter 23, Problem 95CP

(a)

Interpretation Introduction

Interpretation: The structures of 2 and 3, an acid-catalyzed mechanism for the conversion of 3 to 4 and the reasons for the equilibrium favor enamine 4 over imine 3 have to be found for the given reactions.

Concept Introduction:

An azide is converted into an amine through hydrogenation in the presence of platinum or palladium.

To find: Draw the structures of 2 and 3

Do hydrogenation on an azide

(b)

Interpretation Introduction

Interpretation: The structures of 2 and 3, an acid-catalyzed mechanism for the conversion of 3 to 4 and the reasons for the equilibrium favor enamine 4 over imine 3 have to be found for the given reactions.

Concept Introduction:

  An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of H₂O.  The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group containing both alkene (en-) and alcohol (-ol). Enamines are considered to be nitrogen analogs of enols.  If one of the nitrogen substituents is a hydrogen atom, H, it is the tautomeric form of an imine. This usually will rearrange to the imine; however there are several exceptions (such as aniline). The enamine-imine tautomerism may be considered analogous to the keto-enol tautomerism. In both cases, a hydrogen atom switches its location between the heteroatom (oxygen or nitrogen) and the second carbon atom.  Enamines are both good nucleophiles and good bases.

To find: Provide an acid-catalyzed mechanism for the conversion of 3 to 4

Do protonation for imine

(c)

Interpretation Introduction

Interpretation: The structures of 2 and 3, an acid-catalyzed mechanism for the conversion of 3 to 4 and the reasons for the equilibrium favor enamine 4 over imine 3 have to be found for the given reactions.

Concept Introduction:

An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of H₂O.  The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group containing both alkene (en-) and alcohol (-ol). Enamines are considered to be nitrogen analogs of enols.  If one of the nitrogen substituents is a hydrogen atom, H, it is the tautomeric form of an imine. This usually will rearrange to the imine; however there are several exceptions (such as aniline). The enamine-imine tautomerism may be considered analogous to the keto-enol tautomerism. In both cases, a hydrogen atom switches its location between the heteroatom (oxygen or nitrogen) and the second carbon atom.  Enamines are both good nucleophiles and good bases.

To find: Get the reasons for the equilibrium favor enamine 4 over imine 3

Explain the conjugation