Oxime Reduction with NaBH4/NiCl2

[uemura]

Checking for possible methods for reduction of Oximes, Uemura found the NaBH4/NiCl2 method mentioned from time to time in the Hive. But nowhere Uemura could find some details how to do the reduction via this method. Has any bee around a small experimental write-up which could serve as an example how to perform this reaction?
Carpe Diem

[sunlight]

I made the procedure described by Rhodium in TSII with 2,5 DMNS, two times, but yield was low, 20 %. I would use that procedure but changing the amounts for the oxime.
If I remember correctly the original procedure is for unsaturated nitros, and uses a 20 % of NiCl2 and 3.5 molar excess of NaBH4 (including NiCl2 and nitro group).

[Acme]

For reduction of a thioamide it was 8 eq NiCl2, 24 eq NaBH4 in THF at 0 C for 1 H, the yield was 75%

[uemura]

sunlight and acme,
thanks so far. Yield doesn't look good at all when you go with this route. Any other ideas other than Na in EtOH? Carpe Diem

[Rhodium]

There are Al/Hg reductions of oximes on my page too.

[hypo]

friend of mine had no luck with the Al/Hg routes of your page (in the file various reductions of oximes). the ab2 variation (with AcOH) worked.

[Rhodium]

Great, congratulations to Antibody2 then. I believe he did QUITE a bit of experimentation before finding out how to do it the best way.

[twodogs]

Synlett pg 708 1992
Zinc dust 2.6 mols, Copper Sulphate 1.4 mols is suspended in 65% aqueous ethanol and sonicated with a Branson 1200 for 8 minutes at 60C and a conc solution of 1 mol oxime in ethanol is added and the reaction is continued for 3 hours. I haven't got the resulting yield though. Easy if you have access to ultrasound.

[sunlight]

Uenura, I tried the nitrostyrene, that has the dimerization porblem, I would say that if works, yield will be higher for oximes.

[foxy2]

I'll bet Ushibara and NaBH4 together would reduce it.  Probably better than the NiCl2.

Reason being that the NaBH4 most likely reduces the NiCl2 to an active metallic nickel which then catayzes the oxime reduction(IMHO)
Do Your Part To Win The War

[hest]

I think you are making NiBH4

[Rhodium]

NaBH4 and NiCl2 forms the hydrogenation catalyst Ni2B upon mixing (it is a black powder). Excess NaBH4 then furnishes the rest of the hydrogen needed for reduction.

[foxy2]

Ok my bad.
Its just that I thought read something like I stated with LiAlH4.

Oh well.
Do Your Part To Win The War

[sunlight]

Yes, Ni2B. I have a paper that says it's more stable than Raney Nickel and it is more re-usable than the Raney one, but in the nitro reduction reference talks about fresh catalyst. Probably it was fresh just for experimenting purposes, in the other paper states it is completely reusable for hydrogenations.

[uemura]

Bees,
valuable posts! Now, may Uemura come back to the NiCl2/NaBH4 reduction. What he still would like to read is how you actually perform the rxn . Do you mix the NiCl2 with NaBH4 and put it in as a mixed powder, or do you dissolve the NiCl2 in MeOH + oxime and the add the NaBH4 using cold/warm conditions....
You see what Uemura means. Are there helpful bees around with a example write-up??? Thanxxxxs Carpe Diem

[Rhodium]

The NiCl₂*6 H₂O is dissolved in methanol together with the compound to be reduced, and NaBH₄ is added with stirring at room temp.

[Dr_Sister]

Bees - was it not discussed previously that one of the reasons this rxn was not performing well was that bees were skipping the sonification step???

Uemura - why not simply reduce ala ab2? it works well. i'm sure you have you reasons so heres your early xmas present,

Tetrahedron Lett, Vol 26, No52, pp6413-6416, 1985

A 100ml rb flask containing NiCl2-6H20(1.55mmol) and CH3OH (30 mls) 2was sonicated to effect complete solution, then solid NaBH4 (4.65mmol) was added portionwise (frothing!!!). After 30 min nitro (3.1mmol) was added in 2ml CH3OH, followed by more solid NaBH4 (10.9mmol) over 5 minute period, five minutes later tlc indicated all nitro compound had disappeared - i'll leave the work-up to your imagination   .
7.10.01

[uemura]

Thanks Dr_Sister and Rhod,
perhaps Uemura should ask for an ultrasonic cleaner for x-mas.  
Anyway, the oxime route via NiCl2/NaBH4 seems not to bee too promising! Agreed?
Carpe Diem

[Antibody2]

i'd sure like to have an ultrasound bath