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Topic: Synthesis of 2,3-dihydroindole  (Read 3630 times)

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Offline Sharka

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Synthesis of 2,3-dihydroindole
« on: August 05, 2013, 07:34:40 AM »
Can anybody help me with synthesis of 2,3-dihydroindole from 2-nitrotoluene. I need make it up in about seven steps.
This is my solution, but I´m not sure about the last step.
Thanks
« Last Edit: August 05, 2013, 08:41:53 AM by Sharka »

Offline billnotgatez

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Re: Synthesis of 2,3-dihydroindole
« Reply #1 on: August 05, 2013, 07:37:32 AM »
Forum rules require you show some work
Do you have any ideas
Then someone might help
read forum rules

Offline sjb

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Re: Synthesis of 2,3-dihydroindole
« Reply #2 on: August 05, 2013, 01:49:46 PM »
How about a Leimgruber indole synthesis, but not 100% sure of chemoselective reduction after?

Offline rucik5

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Re: Synthesis of 2,3-dihydroindole
« Reply #3 on: August 13, 2013, 07:37:19 PM »
Heyup,
The final condensation step in your synthesis would give you the 'hemiaminal', then elimination of water would produce the imine which would then tautomerize to give you the indole (with the double bond). Also, I'm pretty sure your Grignard formation/reaction would not work on that particular substrate. Any ideas why?

As for the indole reduction, sodium cyanoborohydride in acetic acid can be used to reduce enamines.

See here:
http://chemistry.mdma.ch/hiveboard/picproxie_docs/000503047-ChemicalSocietyReviews_1998_27_excellent_.pdf
or here http://bitnest.ca/Rhodium/chemistry/nabh4.acidic.media-1.html
Note that sodium borohydride gives you the alkylated product.

There's three indole (not indolene) syntheses, starting from nitrotoluene, that I know of. Leimgruber–Batcho, Reissert and Bartolli. That's where I'd start probably.

The only decent list of indolene syntheses I managed to find is here: Nothing from nitrotoluene, but one interesting reference.
http://www.organic-chemistry.org/synthesis/heterocycles/indolines.shtm
(note the indole reduction with Pd(OH)2, ref #5)

I hope I'm not giving away too much. Good luck with the synthesis.
Peter

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