Sciencemadness Discussion Board

imine + R-O-R-MgX

acx01b - 14-2-2012 at 03:43

Hi,

I would like to know if you think that the following reaction will work :

acetone + aniline ---- (molecular sieves 4a, cyclohexane) ---> isopropyl anilimine
CH3-CO-CH3 + Ph-NH2 -----> (molecular sieves 4a, cyclohexane) ----> CH3-C(=N-Ph)-CH3

bromomethyl methyl ether + Mg ----> (THF) ----> bromo magnesium methyl methyl ether
Br-CH2-O-CH3 + Mg ----> (THF) ----> BrMg-CH2-O-CH3

isopropyl anilimine + bromomagnesium methyl methyl ether ----> (H2O) ----> N-isopropyl alpha-methyl methyl ether aniline
CH3-C(=N-Ph)-CH3 + BrMg-CH2-O-CH3 ----> (H2O) ----> CH3-C(CH2-O-CH3)(-NH-Ph)-CH3



I have an other question : why in some synthesis reacting organometallics with imine is done with organolithium and not with organo magnesium. In the reaction I describe will it be better to use Li-CH2-O-CH3 ???

Thank you very much !!
Reno

[Edited on 14-2-2012 by acx01b]

[Edited on 14-2-2012 by acx01b]

[Edited on 14-2-2012 by acx01b]

acx01b - 15-2-2012 at 06:22

I got some reference on the fact that CH3-O-CH2-MgBr is very unstable, and should be formed and kept at -20°C.

I am going to open a new thread to discuss the unstability of CH3-O-CH2-MgBr
Quote:

It was very important to control the temperature during the preparation and use of MeOCH2MgBr. This reagent was found to be unstable at temperatures above -20 C

http://pubs.acs.org/doi/pdf/10.1021/jo902560f



unstability of CH3-O-CH2-MgBr

acx01b - 15-2-2012 at 06:31

Hi,

I found only one paper where they use the organomagnesium obtained from bromomethyl methyl ether and magnesium in THF.

CH3-O-CH2-Br + Mg ----> CH3-O-CH2-MgBr
Quote:

It was very important to control the temperature during the preparation and use of MeOCH2MgBr. This reagent was found to be unstable at temperatures above -20 C

http://pubs.acs.org/doi/pdf/10.1021/jo902560f


I think that there are two possibilities of destruction of CH3-O-CH2-MgBr




  1. rearrangement

    CH3-O-CH2-MgBr ---> CH3-CH2-O-MgBr

    In that case, the temperature should be kept under -20°C during all the reaction.



  2. bimolecular reaction

    CH3-O-CH2-MgBr + CH3-O-CH2-Br ----> CH3-O-CH2-CH2-O-CH3 + MgBr2

    In that case, after all the CH3-O-CH2-Br has been converted to CH3-O-CH2-MgBr, this reaction cannot occur anymore, and so it can go back to positive ambient temperature.




What do you think ? What reaction will occur ? Is there an other reaction that I didn't think of ?


Thank you very much !

GreenD - 15-2-2012 at 07:24

I'm sure it has to do with the Mg wanting that oxygen atom, and so close to an electronegative carbon, You will probably get some kind of bimolecular reaction, yes.

Nicodem - 15-2-2012 at 11:51

I would tend to believe that such alpha-alkoxyorganomagnesium compounds relatively rapidly decompose into the corresponding carbenes and then further.

What you call a "bimolecular reaction" can not occur as it requires methoxymethyl bromide. That is not a decomposition, but a reaction.

acx01b - 15-2-2012 at 13:17

Hello all,

I finally founded a good reference about imines and organo metallics ! Not so easy to find, and it contains many answers.

http://www.chemistry.sc.chula.ac.th/course_info/OrgReact05/F...

The imine R-MgBr reaction will never work, with R-Li it is maybe possible with BH3 as Lewis basis neutralizer, but there is only a little chance ! Most imine / R-Li additions are difficult to perform.
Quote:

What you call a "bimolecular reaction" can not occur as it requires methoxymethyl bromide. That is not a decomposition, but a reaction.


It can occur when you add the Mg to the methoxymethyl bromide !