Rapid NaBH4/NiCl2 reductive amination

Willie · Tue Feb 15, 2005 8:52 pm

Hi!
Is anybody tried this method mentioned in "Total Synthesis II' p/170-171 ? Abstract:

NaBH4 in methanol, catalyzed by nickel boride, can be used to
reduce nitroalkenes to aminoalkanes in about 70% yields in 15
min at room temp. The nickel boride is prepared in situ from
NiCI2*6H20 (nickel chloride hexahydrate) and NaBH4. The method
is general, and can be applied to many conjugated nitroalkenes.

Rapid is not good, isn't it? Very Happy

I was failed on usial plane nitropropene. I suppose that dissolving NaBH4 in methanol solution of NiCl2 at room temperature is not good idea because NaBH4 reacts with methanol ! So the first question is: why methanol? why not an IPA, for instance??
For example do the same but in IPA at 0 temperature. After the solution completed and all the nickel boride precipitated (black colour), then begin the P2NP addition. After all the nitropropene has been added then begin to rise the temperature from 0 to room and even more. The excess of NaBH4 will react with alcohol and the necessary H2 will be generated. For more hydrogeneration add more NaBH4 until you find that reduction is yet.
Is there something wrong in my suggestion? Any comments will be appreciated.

Another way seems to dissolve NaBH4 in methanol at -30. It's not so easy to do this. And what about the deep frost? and how to dissolve P2NP in so cold alcohol?? I don't know...

May be two kind of alcohol is optimal, IPA for nickel boride preparation at 0 and MeOH for hydrogeneration at room temperature?

Finaly to remove the boride by filtering is not so easy and quick. May be it's better to basify the Rm and wait until the red amino-alcohol layer will rise? Then one's can collect it, remove the alcohol and so on.

joe_aldehyde · huxleys associate

never tried it, but since methanol reacts quickly with NaBH4, i don't know what this method is worth. i will try it anyways. if it works, hooray!

transistor child · gnome

Interesting article:
http://www.erowid.org/archive/rhodium/chemistry/nitro2amine.nabh4-nicl2.html

The question is if it really saturates the double bond in good yields...

joe_aldehyde · huxleys associate

i have no idea, but since NaBH4 reduces ONLY the double bond when used alone on nitropropenes, i guess it will do just that when used with NiCl2 and the corresponding substrate.

joe_aldehyde · huxleys associate

someone tried the method of above link tonight, and it really eats up too much NaBH4 to be of great use ISO. for about 100mmol nitropropene, about 20 grams of NaBH4 were needed! addition took more than one hour and was a pain in the ass, someone reported. workup is due today. as willie said, the filtration of nickel boride is a pain in the ass, too, since Ni2B particles are too small. the will pass a porosity 4 glass frit and every filter paper. someone has no celite...

spicybrown · Tue Jun 28, 2005 7:25 am

Somebody I know tried this reduction on 2,5-dimethoxynitrostyrene. A whole bunch of horrible brown tar was obtained, out of which some decently pure 2C-H was painstakingly extracted. Yield was about 15%. A fellow Bee by the name of Starlight (I think.. hmm.. been a while) reported very similar results. Celite is absolutely necessary to filter the nickel boride. This person wouldn't recommend this route.

-SpicyBrown

Star-light · Blacklight bulb

joe_aldehyde · huxleys associate

brown tar? hooray, there we go. how was the base extracted from the tar? in someones case, it would be MDA. any tips welcome, spicy!

spicybrown · Wed Jun 29, 2005 6:09 am

Starlight: Yeah, I figured I might be wrong.. Well whoever it was, their name started with an s. hehehe.

Regarding the brown tar... It has been a couple-few years since this person carried out the reduction. I believe he may have said something like.. the goo was sort of triturated in solvent (can't remember if it was a nonpolar or an acidic aqueous), the goo scraped around with a spatula until he had had enough of messing with the nasty shit (which was quite hard to ultimately clean out of all glassware). The idea here was to dissolve anything that could be dissolved from the tar. I say it might have been acidic water because I kind of seem to recall an acidification coming prior to the formation of the tar... Don't quite remember the procedure anymore.

In the procedure, are the examples given with nitropropenes instead of nitroethenes? Anyway, if one was to try this with a 3,4-methylenedioxy substitution present, I'd say go very slowly with all additions of acids or bases.

-SpicyBrown

joe_aldehyde · huxleys associate

hm ok isomeone got goo after removing the solvent on the rotavap AND after filtration of the Ni2B crap.
the amine (or whatever it may be) oiled out after the addition of acid to the toluene extract as a brown oil. does it mean someone fucked up completely? someone didn't dry the toluene since it was subjected to bandils "azeotropical drying" procedure anyways, upon which the said brown oil occured.