Chapter 23, Problem 91CP

 (a)

Interpretation Introduction

Interpretation: A structure for the alkaloid halosaline, a reason for not getting the product in the given transformation in one step using LAH and a mechanism for the lactone-to-lactam ring contraction have to be found.

Concept Introduction:

Amides on reduction with lithium aluminum hydride followed by water work-up give the corresponding amines.

To find: Draw a structure for the alkaloid halosaline

Get the formation of lithium salt by reduction

(b)

Interpretation Introduction

Interpretation: A structure for the alkaloid halosaline, a reason for not getting the product in the given transformation in one step using LAH and a mechanism for the lactone-to-lactam ring contraction have to be found.

Concept Introduction:

If a compound contains both the azide and lactone ring, lithium aluminum hydride reduces both the groups, azide into the corresponding amine and the lactone ring into the diol groups.  LAH is a non-selective reducing agent.  For example:

To find: Get the reason for achieving the given transformation in just one step (rather than two) using LAH to reduce both the azide and the amide in one reaction flask

Get the formation of lithium salt by reduction

(c)

Interpretation Introduction

Interpretation: A structure for the alkaloid halosaline, a reason for not getting the product in the given transformation in one step using LAH and a mechanism for the lactone-to-lactam ring contraction have to be found.

Concept Introduction:

The simple lactone-to-lactam transformation occurs due to the driving force of amine nucleophiles.  A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction.  All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles.

To find: Provide a mechanism for the lactone-to-lactam ring contraction

Provide the nucleophilic attack in the starting material