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t-butanl to alkene

How can I accomplish the above conversion?

My thoughts:

  1. One way of introducing the double bond, would be using the appropriate Grignard Reagent after oxidation of t-butanol (somehow)

  2. I think that initial conversion to carbonyl compound is necessary - only then can we follow up with nucleophilic addition.

P.S. The question was in the organometallics section of my assignment, possibly hinting that reagents apart from the above species may be used. However, won't it be great if we could design a mechanism using only the starting species and commonly available reagents?

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  • $\begingroup$ Do we have to use the same species given , or some other species could be used ? $\endgroup$
    – Tanuj
    Commented Feb 27, 2018 at 3:35
  • $\begingroup$ I suppose you may use some other species as well, but won't it be great if we could propose a mechanism using the given species and commonly available reagents? $\endgroup$
    – stoic-santiago
    Commented Feb 27, 2018 at 3:41

3 Answers 3

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t-butanol + allyltrimethylsilane + Lewis acid

This is called the Hosoni-Sakurai Reaction (see J. Org. Chem. 2006 71 8516)

Can only find an image for the more common addition to carbonyl compounds but there are examples of additions to alcohols (see the JoC reference)

enter image description here

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  • $\begingroup$ One last thing, could you post the relevant image here? $\endgroup$
    – stoic-santiago
    Commented Feb 27, 2018 at 13:35
  • $\begingroup$ Done, though it is an image of the addition to carbonyls $\endgroup$
    – Waylander
    Commented Feb 27, 2018 at 15:04
  • $\begingroup$ @Waylander, The first step is the Nucleophilic addition to Carbonyls . But if we have tertiary alcohols, How can there be any addition? Don't we need substitution? And wouldn't that be difficult with a normal Lewis acid ? $\endgroup$
    – Soumik Das
    Commented Feb 28, 2018 at 5:11
  • $\begingroup$ See the JoC reference for addition to alcohols. I could not find an image of the addition to alcohols. $\endgroup$
    – Waylander
    Commented Feb 28, 2018 at 9:25
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A dehydration reaction would be your best bet, you could use $\ce{KHSO4}$ or $\ce{TsOH}$ or $\ce{H3PO4}$. The idea would be to turn the $\ce{-OH}$ into water, making it a better leaving group.

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  • $\begingroup$ What after turning OH into a good leaving group? A carbocation is formed, what next? $\endgroup$
    – stoic-santiago
    Commented Feb 27, 2018 at 4:36
  • $\begingroup$ Depending on what reagent you use; you'll have a negative ion - or you can use water as a base to remove the hydrogen from the carbon next to the one with the positive charge. The breaking of the C-H bond will form the C-C double bond. $\endgroup$
    – LukeTowers
    Commented Feb 27, 2018 at 4:43
  • $\begingroup$ Yield will really be nothing. Major would be 3 Methylpropene. $\endgroup$
    – King Tut
    Commented Feb 27, 2018 at 11:14
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What you could do is convert the t-butanol into a tertiary bromide by heating it with concentrated sulfuric acid and then treating it again with hydrobromic acid to get the tertiary bromide. After that, convert into a Grignard by oxidative addition of a Magnesium atom. Then you can just react it with ethylene oxide, and after working it up one more time, we can again heat it under concentrated sulfuric acid to eliminate the hydroxyl and form the double bond.

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  • $\begingroup$ I think you should correct your answer, from using ethylene oxide to using 1,3 propylene oxide instead. Hence the downvote. $\endgroup$
    – stoic-santiago
    Commented Feb 27, 2018 at 5:21
  • $\begingroup$ tertiary Grignards are lousy nucleophiles $\endgroup$
    – Waylander
    Commented Feb 27, 2018 at 11:01

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