Question

Propose a synthesis for \((Z)-9\)-tricosene (muscalure), the sex pheromone for the common housefly (Musca domestica), starting with acetylene and haloalkanes as sources of carbon atoms. CCCCCCCCC=CCCCCCCCCCCCCCCC

Short answer

Question: Describe a possible synthetic route for the preparation of (Z)-9-tricosene, the sex pheromone for the common housefly (Musca domestica), starting with acetylene and haloalkanes as sources of carbon atoms. Answer: A suitable synthetic route for (Z)-9-tricosene involves the following steps: 1. Preparing the intermediates for synthesis from acetylene and an appropriate haloalkane, such as 1-iodotetradecane. This can be achieved via Corey-Fuchs reaction and reduction for the nine-carbon alkene and an alkyne synthesis followed by the treatment with carbon tetrachloride and tributyltin hydride for the 14-carbon alkene. 2. Coupling these intermediates using the Stille coupling reaction with a Pd(0) catalyst, such as Pd(PPh3)4, to form the desired 23-carbon alkene chain with a cis-double bond at the 9th position. 3. Finally, a hydrogenation step using hydrogen gas and a palladium on carbon (Pd/C) catalyst to ensure complete conversion of any remaining alkyne functional groups to the desired alkene product without affecting the (Z)-alkene stereochemistry.

Step-by-step solution

Preparing the intermediates for synthesis from the given starting materials

We'll begin by converting acetylene to the nine-carbon alkyne via Corey-Fuchs reaction followed by reduction. First, treat acetylene with n-BuLi to form a lithium acetylide, then react with carbon tetrachloride, which gives the tributyltin alkyne upon reaction with tributyltin hydride. Reduce the tributyltin alkyne to the alkene with the Lindlar's catalyst to ensure the formation of the (Z)-alkene. Similarly, we can prepare the 14-carbon alkyne from an appropriate haloalkane, such as 1-iodotetradecane, by converting it to the corresponding alkyne using a strong base, followed by the Treatment with carbon tetrachloride and tributyltin hydride.

Coupling reaction to form the target alkene chain

With both alkenes prepared, we can then perform a coupling reaction to form the desired \((Z)-9\)-tricosene. This can be achieved using the Stille coupling reaction, which involves the use of a Pd(0) catalyst, such as Pd(PPh3)4. The catalyst will couple the tributyltin group in the nine-carbon alkene with the iodine in the 14-carbon alkene, forming the desired 23-carbon alkene product with a cis-double bond at the 9th position.

Hydrogenation of any remaining alkyne

To ensure complete conversion of the alkyne moiety to the desired alkene in the final product, the reaction mixture should be treated with hydrogen gas under mild pressure in the presence of a palladium on carbon (Pd/C) catalyst. This step will selectively reduce any remaining alkyne functional groups to alkenes without affecting the desired (Z)-alkene. To summarize, the synthesis of \((Z)-9\)-tricosene can be achieved by preparing the nine-carbon alkene from acetylene and the 14-carbon alkene from a haloalkane, followed by coupling these intermediates using the Stille coupling reaction to form the 23-carbon alkene chain. A final hydrogenation step ensures complete conversion of any remaining alkyne moieties to the desired alkene product.