Mechanism of the reaction [closed]

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

• hello buddy did you try adding the halide resulting in formation of carbocation and the attacking by the oxygen in carboxylic group Feb 11, 2019 at 12:10
• This may enlighten you en.wikipedia.org/wiki/Iodolactonization Feb 11, 2019 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 :

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

• this is not the accepted mechanism for halolactonisation. See the reference given above Feb 11, 2019 at 13:46
• @Waylander Sir I have corrected it Please reconsider it Feb 11, 2019 at 13:58
• 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. Feb 11, 2019 at 14:04
• @Waylander I just noticed it can you please explain why it is so.... Feb 11, 2019 at 14:06
• 5-exo-Tet is always favoured over 6-endo-tet by Baldwin's Rules reading.ac.uk/acadepts/sd/pharmacy/public_html/staff/andre/… Feb 11, 2019 at 14:27