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question 1:

In the synthesis, both intra- and intermolecular SN2 can undergo, in which only intramolecular reaction gives the cyclic ethers. However, both reactions happen in the reaction mixture. How can I alter the reaction conditions / add other reagents such that the intramolecular reaction becomes more favorable?

One solution I found is diluting the solution since the rate of 2nd order (intermolecular) reaction drops faster than 1st order (intramolecular) reaction. However, I wonder is it practical to dilute the solution to a large extent for purity, compromising the increased reaction duration and is there any faster and simpler reactions?

question 2: This synthesis involves SN2, so I am thinking if there is a tertiary carbon bonded to the leaving group, it is impossible to form a cyclic ether. Therefore, are there any other ways I can synthesis cyclic ethers with the starting material as monohaloalcohol?

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  • $\begingroup$ This is not an epoxide that you are making $\endgroup$ – Waylander Jul 28 at 11:27
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    $\begingroup$ High dilution is a well-recognised technique for favouring intramolecular cyclisations over inter, particularly in the cases of forming large rings $\endgroup$ – Waylander Jul 28 at 12:21
  • $\begingroup$ @Waylander Thanks for reminding. But may I ask under high dilution, what is the typical duration for the reaction? $\endgroup$ – 234ff Jul 28 at 12:30
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    $\begingroup$ Suspended NaH in refluxing diethyl ether. Add bromoalcohol in ether dropwise to the base. You will have to separate ether from the cyclic ether (THF). Notice I didn't use THF as a solvent.;) $\endgroup$ – user55119 Jul 28 at 12:37
  • $\begingroup$ High dilution reactions can be many hours with the reactant added by syringe pump. $\endgroup$ – Waylander Jul 28 at 14:02

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