foxy2
(Distinctive Doe)
02-05-02 12:00
No 265571
      Reductive Amination for primary amines
(Rated as: excellent)
    

Hmmm
This might bee useful.
Looks better than the Leuckart
Foxy

One-pot, new stereoselective synthesis of endo-tropanamine
M. Allegretti, V. Berdini, M.C. Cesta, R. Curti, L. Nicolini and A. Topai
Tetrahedron Lett. 42(25), 4257-4259 (2001)

Abstract
A palladium-catalyzed redn. of ketones to primary amines by reaction with ammonium formate in aq. methanol is described.  The proposed method provides a one-pot synthesis of 3-endo-tropanamine in high yields and stereoselectivity. 

General procedure for the synthesis of 3-endo-tropanamine 3

A solution of 8-methyl-8-azabicyclo[3.2.1]octan-3-one (1) (6 g, 43 mmol) in MeOH (112 mL) was treated, with vigorous stirring, with ammonium formate (25 g, 0.40 mol) and water (12.5 mL). After complete dissolution, 10% Pd/C (5.1 g, 4.8 mmol) was added and the reaction mixture was stirred overnight at room temperature. On completion of the reaction (TLC, eluent: EtOH/NH4OH, 8:2), the catalyst was filtered off on Celite and the solution was concentrated under reduced pressure; the oily residue obtained was dissolved in EtOH (100 mL) and to the solution 37% HCl (7.5 mL) was added dropwise. The solution was seeded and left stirring at room temperature for 1 h and at 4°C for 5 h. The resulting white precipitate was filtered and dried at 40°C under vacuum to give endo-8-methyl-8-azabicyclo[3.2.1]octane bis hydrochloride (7.6 g, 35.6 mmol) in 83% yield; mp >360°C.

Other ketones aminated
MEK                Yield 95%
MIBK               Yield 92%
Cyclohexanone      Yield 65%
1-Methyl-4-Piperidone Yield 75%
some THP ketone    Yield  80%
 
 
 
 
    Osmium
(Stoni's sexual toy)
02-05-02 13:42
No 265599
      Re: Reductive Amination for primary amines     

Damn! That's a nice one!

I'm not fat just horizontally disproportionate.
 
 
 
 
    sunlight
(Pioneer Researcher)
02-07-02 15:40
No 266667
      Re: Reductive Amination for primary amines     

I made a small test and it seems not satisfactory. Having that the amount of Pd/C used in the reference makes it almost unworkable for practical purposes, I used much less catalyst.
2 grams of ketone, 100 mg 10 % Pd/C and 7.7 grams of am. formate in 30 ml of methanol and 3 of water. It was stirred one hour and half, not all am. formate was dissolved, then I added the Pd/C and rxn started immediatly with some effervescence, gasses were directed to a glass with water and I saw about 1 bubble each 6 seconds, one hour later, I warmed up a bit the rxn because there were less bubbles, and so on during 6 hours or so. Then the system was carried to reflux about one hour till there were not more bubbles.
A TLC showed all initial ketone was consumed, and it was a long spot that seemed to contain two different spots, and noone of them was where it should be.
Methanol was evaporated and rxn acidified with dilute HCl, and then appeared too much insoluble organics. I washed it with DCM, basified, extrated with toluene and now it is drying with KOH. I would say there's very little MDA if there's something.
It seems that the am formate reduces readily the ketone, probably to the alcohol and then to the alkane, as it is said in CTH references, but I'm surprised, I thought it would be necessary reflux conditions in acetic acid.
I'll post the results of the workup, but my first impression is that we have a problem that is similar to the NaBH4 procedure, it is not too much imine to reduce, and then the reducing agent reduces the ketone to alcohol in the case of NaBH4 or alcohol and alkane with CTH. Probably the imine should be formed previously, and then reduced with the CTH system. I think that water was added just to solubilize the ammonium salt, that is both the aminating and reducing agent, but it could be a problem with our loved ketone.
 
 
 
 
    foxy2
(Distinctive Doe)
02-07-02 23:58
No 266813
      Re: Reductive Amination for primary amines     

Hmmm
Thats confusing.  A difference in catalyst could bee the problem.  In the article they attempted without water and the yeilds were low.

Since addition of water disfavors imine formation they hypothesize that the reaction proceeds thru direct reduction of the hemiamino intermediate, instead of thru the imine.  Hemiamino has both an alcohol and amine on the same carbon.

Wonder if you may have reduced the benzene ring?

Fully Informed Jury! (http://www.fija.org/)
 
 
 
 
    sunlight
(Pioneer Researcher)
02-08-02 09:17
No 266960
      Re: Reductive Amination for primary amines     

I got 458 mg of salt, what is about a 19 %. Even considering a healthy margin of error working with this small amounts, and that the product is really MDA (I'll make a mp test) it is far from being a good yield with my procedure. Although at least half part of rxn was below 40 C, I wonder if temp can decrease the yields.
 
 
 
 
    sunlight
(Pioneer Researcher)
02-09-02 17:30
No 267568
      Re: Reductive Amination for primary amines     

I made another test, but this time using the exact ratios of the reference except the Pd/C, I reused the above 100 mg and 2 grams of my loved ketone. The rxn was stirred at roomp temp (20 C or so), and when I come home again, 28 hours later, I made a TLC and it was exscyly like the other. This time instead of use a sample of ketone to contrast it, I put a sample of the amine, and I was worng in may first interpretation of the TLC, the long spot seems to be formed with two spots, with a from that could be compared with a guitar (more or less), and the spot in the bottom match with the amine. The smell of rxn remeber me the NaBH4 rdxns, so it could be the alcohol. And it's amazing that the ketone is reduced completely in so mild conditions.
The solution was filtered, concentrated and acidifiecd with dilute HCl, and it appeared again too much undissolved oraganics, more or less the same than in the previous test.
I don't believe that more catalyst could be better, but I don't know.
May be adding aqueos NH3 instead of water can help the rxn.
Anyway this rdxn is very interesting, and may be can work with other interesing ketones.
Thanks foxy for your work. We'll keep this rxn in mind, as I told I thought about it before so it has been comfortable to see it was not a nonsense. May be we can find something better someday.
 
 
 
 
    sunlight
(Pioneer Researcher)
02-12-02 00:01
No 268454
      Re: Reductive Amination for primary amines     

Foxy2, thanks again for your input. If I am interpreting correctly the TLC, and I think so, I've found something that can be good. It's very soon to talk about it, I must elaborate it before. You said it, room temp, water, atmospheric pressure...
And, I don't know why, but I've always thought that CTH reductions only could take place in anhydrous conditions, or just with the water formed in rxn. These CTH rdxns have now a new interest for me, they are easy, clean and not hazardous taking a bit of care.
I've read in the Hive (that's is my source of knowledge together with Merck Index), that CTH in THF reduces nitropropenes to oxime (Cyrax), but also Rhoidum told taht oximes are reduced with CTH rxns, can anyone clarify this point ?
 
 
 
 
    Rhodium
(Chief Bee)
02-12-02 00:17
No 268466
      Re: Reductive Amination for primary amines     

It might have to do with the amount of formate present, reaction time, acidity etc. Different reaction conditions, different products.
 
 
 
 
    foxy2
(Distinctive Doe)
02-12-02 00:30
No 268471
      Re: Reductive Amination for primary amines     

"And, I don't know why, but I've always thought that CTH reductions only could take place in anhydrous conditions, or just the water formed in rxn."

You may bee thinking of Imine formation which is inibited/reversed by the presence of water.  The authors also were puzzled that water increased yeilds.  This lead them to propose an alternate reduction mechanism that bypasses the imine by direct reduction of the hemiaminal intermediate I mentioned above.

I'll try to get you the details.
Foxy

Stay Informed (http://www.mapinc.org/)
 
 
 
 
    sunlight
(Pioneer Researcher)
02-12-02 07:38
No 268595
      Re: Reductive Amination for primary amines     

No, foxy, it was just in the reference posted in the hive says  "anhydrous ammonium formate"... And yes, I'm testing the rxn in microscale with TLC, and the aqueous system seems to be better than the anhydrous one, it's surprising.
Ok Rhodium, so we have new perspectives, CTH for reductive amination, nitroalkane rdxn, carbonyl groups and even oximes.
 
 
 
 
    Rhodium
(Chief Bee)
02-12-02 07:42
No 268600
      Re: Reductive Amination for primary amines     

The reason they use "anhydrous ammonium formate" is probably due to the fact that if it is partially hydrated, an exact molar amount cannot be weighed out.
 
 
 
 
    sunlight
(Pioneer Researcher)
02-12-02 07:46
No 268604
      Re: Reductive Amination for primary amines     

Yes, yes, and they flushed argon as well. I understand it is to give a standarized procedure, but it confused me.
 
 
 
 
    Rhodium
(Chief Bee)
12-12-03 14:49
No 476488
      Pd/C & NH4OAc Reductive Amination of P2P's
(Rated as: excellent)
    

CAL-B-catalyzed resolution of some pharmacologically interesting beta–substituted isopropylamines
Javier González-Sabín, Vicente Gotor,  and Francisca Rebolledo
Tetrahedron: Asymmetry 13(12), 1315-1320 (2002)
DOI:10.1016/S0957-4166(02)00336-1


Synthesis of racemic amines. General procedure.

A slight modification of a reported method [17] was adopted for the synthesis of these compounds. To a solution of the appropriate phenylacetone (20 mmol) in deoxygenated methanol (52 mL), water (6 mL) and ammonium formate (0.21 mol) were added. After complete dissolution, 10% Pd/C (0.80 g, 0.75 mmol) was added and the mixture stirred at room temperature until disappearance of the ketone (TLC control, ethyl acetate: methanol, 4:1). Then, the catalyst was filtered on Celite®, washed with methanol and the solvents were evaporated. The residue was treated with conc. aq. HCl (4 mL) and water (30 mL) and extracted with diethyl ether (2×20 mL). Aqueous phase was treated with solid NaOH until pH basic, and extracted with diethyl ether (3×25 mL). Evaporation of the organic phase yielded the corresponding amine. A second fraction of amine was obtained by continuous extraction of the basic aqueous phase (dichloromethane, 14 h). Crude amine was purified by distillation under reduced pressure. Distillation temperatures (0.5 Torr) and yields of the amine are as follows:

Amphetamine, 1 (45°C, 80%)
o-MeO-Amphetamine, 2 (68°C, 75%)
m-MeO-Amphetamine, 3 (72°C, 72%)
p-MeO-Amphetamine, 4 (60°C, 79%)


References
17.
Tetrahedron Lett. 42, 4257–4259 (2001) (../rhodium/pdf /redamin-pdc-af.pdf)
Post 265571 (foxy2: "Reductive Amination for primary amines", Methods Discourse)

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