I need to convert the starting material to the product on the right but I was wondering if it was possible to use a Diels-Alder reaction and use $\ce{KMnO4}$ to cleave the ring.
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$\begingroup$ A better way would be the tetramerization of ethyne to cyclooctatetraene, then hydrogenation to cyclooctene followed by ozonolysis. $\endgroup$– aventurinApr 21, 2018 at 23:25
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$\begingroup$ what is tetramerization? $\endgroup$– ChemApr 22, 2018 at 1:56
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$\begingroup$ The combination of 4 molecules (monomers, here ethyne) to a single molecule (here cyclooctatetraene). $\endgroup$– aventurinApr 22, 2018 at 8:31
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1 Answer
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You can obviously use Diels-Alder Reaction for the synthesis of the desired product but not so directly. But Diels-Alder will give an optimal yield when the ring formed is Six-Membered. After the formation of that Six-Membered product, you have to increase the no. of carbon atoms in the carbon-chain by some way, and the yield of your product will be also better if you no. of steps as less as possible.
I will not suggest you to directly add 1,3-butadiene to acetylene because there will be a chance of aromatisation, and then you cannot do anything, as to break the aromatic rings are highly unfeasible. Instead I can suggest you the following steps:
- First you partially reduce the acetylene to ethene, and then perform Diels-Alder reaction with butadiene. You will get cyclohexene.
- In the second step, you perform ozonolysis, and then to the resulting compound, perform Wittig reaction with excess reagents. You will get octa-1,7-diene.
- Lastly, you can perform hydroboration, oxidation to get less substituted diol, and then oxidise that to acid by any strong oxidising agent like $\ce{KMnO4}$ or $\ce{K2Cr2O7}$ in slightly acidic medium.
Thus, you will get your desired product. The path of reaction is shown below:
answered Apr 21, 2018 at 8:54
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$\begingroup$ is it possible to use h2 pd/c instead of the witting reaction to reduce the oxygen? My professor never taught that reaction so I don't know the mechanism. $\endgroup$– ChemApr 21, 2018 at 19:31
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$\begingroup$ NO! You cannot. The reduction by $H_2/Pd $ will reduce the double bond too and you can't proceed further. In fact this reagent can reduce almost everything to saturated forms , which are not always desired. That 's why different reducing agents are made which can reduce to certain extent according to our choice. $\endgroup$ Apr 22, 2018 at 4:34
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$\begingroup$ Please also observe that by Wittig reaction, I am increasing the no of Carbons in the chain. You cannot do it by using a reducing agent.. $\endgroup$ Apr 22, 2018 at 4:38