Chapter 26.8, Problem 28CC

Interpretation Introduction

Interpretation:

A mechanism for biosynthesis of $\alpha$-farnesene starting with dimethylallyl pyrophosphate and isopentenyl pyrophosphate need to be drawn.

Concept introduction:

Terpenes are constructed from dimethylallyl pyrophosphate and isopentenyl pyrophosphate.  In the synthesis of terpene pyrophosphate is the leaving group as it is a weak base. Nucleophilic attack happens to form another carbocation.  Finally proton transfer happens to give the final product.

The terpene synthesis involves the following steps,

• Loss of OPP (pyrophosphate group)
• Nucleophilic attack
• Deprotonation

The above three steps are repeated again and again.  In each step and isoprene unit is added more.  Finally to obtain $\alpha$-farnesene, the formed farnesyl pyrophosphate undergoes elimination.

To draw: a mechanism for the given transformation.