Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: How about a problem of the week why not?  (Read 1669 times)

0 Members and 1 Guest are viewing this topic.

Honclbrif

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +58/-9
  • Offline Offline
  • Gender: Male
  • Posts: 659
How about a problem of the week why not?
« on: February 28, 2012, 04:48:57 PM »

The following three step one pot transformation has been reported in fair to good yields. Propose a mechanism to account for the observed product. For the purposes of the mechanism, assume that no reagent greatly exceeds 1 equivalent.

Logged
Individual results may vary

Rory

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 13
Re: How about a problem of the week why not?
« Reply #1 on: February 28, 2012, 11:34:38 PM »

Let me have a try.
Nucleophilic addtion of tBuLi to the isocyano group followed by insertion of the CO gave the acetyllithium which tautomized to a carbene. Then 6 pi electrocyclization to form a more stable lithium enolate and subsequent [1,5]-sigmatropic alkyl migration to achieve rearomatization, delievered the 3-H indole derivative which was methylated to furnish the target molecule.
Logged

Honclbrif

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +58/-9
  • Offline Offline
  • Gender: Male
  • Posts: 659
Re: How about a problem of the week why not?
« Reply #2 on: February 29, 2012, 12:57:52 AM »

The reaction of carbanions with CO is known to form acyl lithiums, but in this case it does not tautomerize to a carbene.
Logged
Individual results may vary

Rory

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 13
Re: How about a problem of the week why not?
« Reply #3 on: February 29, 2012, 01:45:22 AM »

The reaction of carbanions with CO is known to form acyl lithiums, but in this case it does not tautomerize to a carbene.
When I said the acyl lithium tautomerized to the carbene, I meant the acyl anion resonated to the carbene. Taking the Lithium into account, I must call them tautomers. An alternative pathway is intramolecular Michael addition that would lead to the same enolate, though I prefer the electrocyclization pathway.
Logged

Honclbrif

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +58/-9
  • Offline Offline
  • Gender: Male
  • Posts: 659
Re: How about a problem of the week why not?
« Reply #4 on: February 29, 2012, 03:19:48 AM »

I do like the electrocyclization, but the reference I'm consulting claims a pathway with a further intermediate.
Logged
Individual results may vary

Rory

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 13
Re: How about a problem of the week why not?
« Reply #5 on: February 29, 2012, 03:55:18 AM »

I do like the electrocyclization, but the reference I'm consulting claims a pathway with a further intermediate.

Well, actually there were at least 3 possible pathways for this transformation and I posted the one I like most at first. Maybe the answer you want is the one including a ketene intermediate.
Logged

Honclbrif

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +58/-9
  • Offline Offline
  • Gender: Male
  • Posts: 659
Re: How about a problem of the week why not?
« Reply #6 on: February 29, 2012, 04:01:38 AM »

That would be the published mechanism.

Orita, Akihiro; Fukudome, Masato; Ohe, Kouichi; Murai, Shinji
Journal of Organic Chemistry,   1994 ,  vol. 59,  # 2   p. 477 - 481

This one came up on our mechanism board a while ago and four different people each got four different pathways, each of them arguing passionately for their own. I figgured this might be a fun one to send to the internet then.

Personally I like the electrocyclization pathway best too, but i figured it would be best to ask for an answer here where I can give a solid reference.

Well done Rory!
Logged
Individual results may vary
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.058 seconds with 24 queries.