Chapter 24, Problem 24.27P

Interpretation Introduction

Interpretation:

The mechanism of the reaction given in the question has to be given.

Concept Introduction:

Cross coupling:

A cross coupling reaction is defined as a reaction that creates a $\text{C}-\text{C}$ bond by coupling together two alkyl, aryl, alkenyl or alkynyl groups.  Cross coupling reactions involve a transmetallation step.  A transmetallation is a pairwise interchange of ligands between two different metals or metalloids.

In the case of palladium catalysed cross-coupling reactions the other metal or metalloids are commonly $\text{Zr,}\text{Sn}\text{,}\text{B}\text{,}\text{ZN}\text{,}\text{Cu}\text{,}\text{Mg}$ which are designated as M in the following general example,

$\text{R-Pd}\text{+R'-M}\stackrel{}{\to }\text{R'-Pd}\text{+}\text{R-M}$

Stille coupling:

The $\text{Pd(0)}$ catalyzed cross-coupling reaction which involves the use of aryl or vinyl tin reagents (known as stannens) as the transmetalling agent is called the Stille coupling reaction.  Coupling with another vinyl or aryl group leads to the creation of conjugate dienes or an alkenylarene.  The coupling occurs with regioselectivity and retains the stereochemistry from the reactants to the products.

$\text{R-X}{\text{+R'-SnR}}_{\text{3}}^{\text{''}}\stackrel{{\text{PdL}}_{\text{n}}}{\to }\text{R'-R}\text{+}{\text{X-SnR}}_{\text{3}}^{\text{''}}$