I came across the following reaction,about which I was ignorant till now.Can anyone guide be regarding it with suitable mechanism.enter image description here


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  • $\begingroup$ hello buddy did you try adding the halide resulting in formation of carbocation and the attacking by the oxygen in carboxylic group $\endgroup$ – Advil Sell Feb 11 at 12:10
  • 5
    $\begingroup$ This may enlighten you en.wikipedia.org/wiki/Iodolactonization $\endgroup$ – Waylander Feb 11 at 12:40

These reaction are called as Lactonization(Generally) these follow a pretty straightforward mechanism the steps are as follow:

  1. The $\ce{HCO3-}$ ion from $\ce{NaHCO3}$ Deprotonate the oxygen of carboxylic group to give a negative charge on the oxygen atom
  2. Meanwhile the doublebond forms a non-classical carbocation with $\ce{I2}$
  3. The Oxygen atom attacks the non-classical carbocation forming a six membered ring and a $\ce{I}$ on the adjecant atom

This is the mechanism scheme of the above description : enter image description here

A similar approach can be followed for the $2^{nd}$ reaction.

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    $\begingroup$ this is not the accepted mechanism for halolactonisation. See the reference given above $\endgroup$ – Waylander Feb 11 at 13:46
  • $\begingroup$ @Waylander Sir I have corrected it Please reconsider it $\endgroup$ – Advil Sell Feb 11 at 13:58
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    $\begingroup$ It is worth noting that in the second example the [5] ring is preferred over [6]. This is a general rule of preference for these kind of reactions. $\endgroup$ – Waylander Feb 11 at 14:04
  • $\begingroup$ @Waylander I just noticed it can you please explain why it is so.... $\endgroup$ – Advil Sell Feb 11 at 14:06
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    $\begingroup$ 5-exo-Tet is always favoured over 6-endo-tet by Baldwin's Rules reading.ac.uk/acadepts/sd/pharmacy/public_html/staff/andre/… $\endgroup$ – Waylander Feb 11 at 14:27

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