Chapter 13, Problem 13.2P

Interpretation Introduction

Interpretation:

The appropriate precursors to the given target, by applying a transform that undoes the reaction in entry 2 of Table 13-1, are to be drawn.

Concept introduction:

Synthesis may be designed by thinking in the reverse direction, from the product to the starting compound, in a method called retrosynthesis. Retrosynthesis involves starting with the product and determining a suitable precursor from which it can be synthesized, without considering specific reactions. The precursor must be a simpler molecule, which may or may not have a close structural relation to the target molecule. This process is repeated until an easily available (or easily prepared) precursor is reached. Each of these steps is called a transform. The reaction in entry 2 in Table 13-1 suggests that the terminal alkyne, on deprotonation with the strong base, generates alkynide ion which serves as a nucleophile. This nucleophile attacks the less substituted carbon of the epoxide ring to open the ring via ${\text{S}}_{\text{N}}\text{2}$ mechanism. An alkoxide ion is formed, which on acidic workup, turns to an uncharged alcohol molecule. This reaction suggests that one can change or alter the carbon skeleton without altering the triple bond. These reactions are the step-up reactions that involve the formation of the new carbon-carbon bond involving a terminal alkyne.