Chapter 24, Problem 24.8P

Interpretation Introduction

Interpretation:

When the starting alkene has ${\text{CH}}_{\text{2}}$ as its terminal group, Hech reaction is highly stereoselective for formation of E-isomer.  The mechanism has to be proposed for this stereoselectivity.

Concept Introduction:

Heck reaction:

A palladium-catalyzed reaction of the carbon group of a haloalkene substituted for a hydrogen on double bonded carbon of an alkene is said to be Heck reaction.

Explanation of Solution

The given reaction is

Mechanism:

Step-1:

Formation of Heck catalyst:

Heck catalyst s formed by the reduction of palladium from $\text{Pd(II)}$ to $\text{Pd(0)}$ by forming the complex with two molecules of ligands.  The ligand used is triphenylphosphine.  The reducing agent used is triethylamine.

Step-2:

Catalytic cycle for the formation of product:

The addition of alkene to the catalyst is syn addition and elimination of product is also syn elimination.  The inversion of configuration occurs in the addition and forms E-product.