Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: Weinreb amide to aldehyde in the presence of an ester  (Read 295 times)

0 Members and 1 Guest are viewing this topic.

Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +233/-16
  • Offline Offline
  • Posts: 3607
Weinreb amide to aldehyde in the presence of an ester
« on: February 09, 2019, 08:29:30 AM »

I was looking over a synthesis recently in which a Weinreb amide was made and then reduced with DIBAL.  It was done in the presence of a tertiary-butylester.  Would there be some chance that the ester would also reduce?  Are there any special tricks when making aldehydes with DIBAL?  There was a thread here a few years ago, which mentioned this reduction, but there was not much discussion about it.
Logged

zarhym

  • Full Member
  • ****
  • Mole Snacks: +13/-1
  • Offline Offline
  • Gender: Male
  • Posts: 115
    • Linkedin
Re: Weinreb amide to aldehyde in the presence of an ester
« Reply #1 on: February 10, 2019, 03:50:25 PM »

tert-Butyl esters are less reactive in reduction compare to weinreb amide.
In my experience, reduction of weinreb amide to aldehyde requires low temperature (-78 to 0°C) to provent over reduction.

You can read this paper for more infomation.
https://onlinelibrary.wiley.com/doi/pdf/10.1002/bkcs.10571

You can check the table 3 in this paper to compare the reduction on ester and weinreb amide.
Logged

Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +233/-16
  • Offline Offline
  • Posts: 3607
Re: Weinreb amide to aldehyde in the presence of an ester
« Reply #2 on: February 11, 2019, 06:51:37 AM »

Thank you; this paper looks quite helpful.
Logged

pgk

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +76/-21
  • Offline Offline
  • Posts: 716
Re: Weinreb amide to aldehyde in the presence of an ester
« Reply #3 on: February 11, 2019, 07:58:16 AM »

Theoretically, DIBAL reduction occurs via formation of a >=O-Al Lewis complex that forces the hydride to attack from the less bulky side, which is impossible in case of a bulky tertiary ester, especially in low temperatures.
(But I have never worked with DIBAL and thus, I cannot know what happens in real life.)
 
« Last Edit: February 11, 2019, 08:14:17 AM by pgk »
Logged
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.063 seconds with 24 queries.