9. Alkenes and Alkynes

Show how you would synthesize the following compounds from acetylene and any other needed reagents:

(a) 6-phenylhex-1-en-4-yne

(b) cis-1-phenylpent-2-ene

Muscalure, the sex attractant of the common housefly, is cis-tricos-9-ene. Most syntheses of alkenes give the more stable trans isomer as the major product. Devise a synthesis of muscalure from acetylene and other compounds of your choice. Your synthesis must give specifically the cis isomer of muscalure.

For each of the following target molecules, design a multistep synthesis to show how it can be prepared from the given starting material:

d.

Propose structures for intermediates and products (F) through (G)

Beginning with acetylene and benzyl bromide and using any other inorganic reagents, propose a synthesis of the alkene shown here.

Show how the following compounds can be synthesized starting with ethyne:

a. cis-2-octene

Show how you would accomplish the following synthetic transformations. Show all intermediates.

e. 2,2-dibromohexane → hex-1-yne

When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]

(c)