I've been trying using NaBD4/NiCl2·6H2O/Boc2O to reduce nitrile into d2-primary amine.
A pretest using NaBH4 ran smoothly but when NaBD4 was used LC-MS showed that the product is a mixture of di-deuterated and mono-deuterated product (almost 1:1 ) together with minor undeuterated product.
The solvent is MeOH, also, the NiCl2·6H2O may account for the H-source. But the mechanism should involve this H-D exchange with NaBD4 how could I improve this reaction?
PS: The substrates also bears a carboxylate, in this sense reduction by LiAlD4 is not considered.
Thanks!
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update :
Sorry for my rough description above.
The operation is modified from Journal of Medicinal Chemistry, 2009, Vol. 52, No. 16 (see attachment) In Scheme 7. I wish to use isotope products thus NaBD4 is used. However the catalyst(NiCl2·6H2O) and solvent (MeOH) is not deuterated as I presume that only NaBD4 play the role of reductant and the deuterated product should be obtained exclusively.
Now that the result is obtained in a mixture of mono-/di-D-substitued compounds as shown in the picture (see attachment)， how can I improve my result?
Salam , why you used deuterated reducing agent ?what is your point .
Is your amine an aromatic or aliphatic amine? there seem to be difference in the reagent conditions used.
The Boc2O should be protecting the primary amine leading to the monodeuterated product when the Boc is removed possibly during the workup. It depends on the reaction procedure.
Even if a 1:1 products mixture may be purified to recover the compound of interrst if you wish to improve the reaction yield you should consider the following points.
Isotopes may have a lower velocity of reaction which may require longer reaction time.
You may try to eliminate the crystallization water from the Ni salt prior the use. 180°C in an oven until constant weight should be a useful treatment to do this. If the hydrated form is required you may try to crystallize the dry salt (after the oven treatment) from D2O. The dry salt should be kept in a desiccator to avoid the capture of environmental moisture.
dear Alaa J Mahrath,
I am trying to prepare the d2-phenylmethanamine( with two-Deuterium on the methylene) as the building block to verify the hydrogen-transfer in further work. And a carboxylate is also on this moiety, thus limited reductant is available in this reaction.
Dear Eugene Yang,
Sorry for my poor expression that you might have misunderstood my problem. I've updated it in a more specific way, thanks anyway O(∩_∩)O
I think the problem could be due to the NiCl2 being used in catalytic amount so not all the deuterated borohydride is converting to the Nickel boride, especially after the first hydride is added to the carbon to form an imine type compound which should react quite readily with NaBH4. Maybe you can try with stoichiometric amount of NiCl2, the authors of the original method discuss it further in their paper.
S. Caddick, D. B. Judd, A. K. de K. Lewis, M. T. Reich, M. R. V. Williams, Tetrahedron, 2003,59, 5417-5423. 10.1016/S0040-4020(03)00858-5
Hope it helps your work!
Dear Rengwei Sun,
As the NiCl2-6H2O is used in a catalytic amount, it seems unlikely that it is the primary source of hydrogen. Based on your description, it seems more likely that the hydrogens are coming from the solvent. Although I'm not entirely sure of the mechanism on how this occurs, a quick fix would be to try the reaction on small scale using deuterated methanol. You can use CD3OD, but you can also purchase CH3OD, where only the alcoholic oxygen is deuterated. It's much cheaper than the fully deuterated version, but should still work.
If this test reaction works, you can scale up. Good luck!
Same. You should use a anhidrous nickel source and a deuterated solven in order to avoid H/D exange. Moreover, try to take the same care with the workup!
Regards!
I agree, you should use deuterated Ni catalyst and CD3OD in your reaction, they both should not be very expensive comparing to NaBD4. You can exchange H2O to D2O in NiCl2-6H2O by dissolving the latter in D2O and evaporating the mixture, or simply recrystallizing NiCl2-6H2O from D2O (perhaps few times).
Also do not forget about work-up - you may need to use D2O at this stage as well.
Good luck !
i am facing same issue i got 3.34% unconverted CH2 protons present in deutrated compound i calculated deutrium % through NMR but i want to calculate unconverted H through LCMS .if any body knows please let me know it will help me more to study Rengwei Sun Alaa J Mahrath Eugene Yang Alessandro Venditti
Dear Dr Nadarajan
Yo should give more details about both the synthetic procedure you are conducting and the analytical approach you have planned to apply.
Regards,
Alessandro
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