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Topic: Does anyone know this mechanism?  (Read 2558 times)

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Offline livelaughlove00

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Does anyone know this mechanism?
« on: February 03, 2017, 10:49:55 PM »
I completely understand where the first reagent comes into play. But for the duels-alder reaction to occur, the single double bond needs to positioned differently and made into two double bonds. So, I figured NBS would add bromide to the cyclopentene and then Bu4N+I- would abstract the proton to displace double bond positioning. First of all it's not strong enough of a base to do that AND it does not lead to an I-Br byproduct. Please help for good karma!

Offline orgopete

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Re: Does anyone know this mechanism?
« Reply #1 on: February 09, 2017, 02:05:01 PM »
I don't agree with the formation of bromo-iodide. It is a product of a net reduction (electron donation). Formation of a diene requires a net oxidation (electron loss). A loss of bromide (such as HBr) would accomplish this. This reaction needs a (weak?) base and probably simultaneous with the Diels-Alder reaction.
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Offline clarkstill

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Re: Does anyone know this mechanism?
« Reply #2 on: February 16, 2017, 10:40:45 AM »
Was the 'hint' just mis-spoken? I can imagine TBAI reacting with NBS to form IBr as a more electrophilic source of 'Br+'. Then just do a C3-bromination of the indole followed by an elimination (presumably the succinimide anion is the base?), remove a proton to turn the N-acyl iminium into the enamine and you're ready to go. Thoughts?

Offline orthoformate

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Re: Does anyone know this mechanism?
« Reply #3 on: March 05, 2017, 01:31:08 AM »
could radical allylic bromination followed by elimination be feasible explanation?

Offline orthoformate

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Re: Does anyone know this mechanism?
« Reply #4 on: March 05, 2017, 01:35:08 AM »
Was the 'hint' just mis-spoken? I can imagine TBAI reacting with NBS to form IBr as a more electrophilic source of 'Br+'. Then just do a C3-bromination of the indole followed by an elimination (presumably the succinimide anion is the base?), remove a proton to turn the N-acyl iminium into the enamine and you're ready to go. Thoughts?

I agree, this makes sense.

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