Simpler reduction of amino alcohols to amines
I was looking at a typical synthetic scheme for reducing amino alcohols, which goes as follows in the image below:
1. Reduction with borane/THF, LiAlH4, etc.
2. Boc protection of amine
3. Conversion of alcohol to a leaving group such as iodine, bromine, or tosylate
4. Reduction with LiAlH4
5. Boc deprotection
The issue with this is it isn't particularly accessible to the amateur, as Boc anhydride is very expensive and only available from chemical suppliers
that often don't sell to individuals. It's also five steps, which is less than ideal.
Rading about reductions, I was thinking of a simpler scheme, that could achieve the same reduction in just three steps, with no need for Boc
anhydride.
1. Reduction with borane/THF, or Red-Al, LiAlH4, etc.
2. Tosylation
3. Reduction with Red-Al
This was based on a reference in Organic Synthesis which claims that Red-Al is capable of reducing toluenesulfonamides, and that simplifies
out the protection step, where the treatment of the amino alcohol with two equivalents of tosyl chloride has the function of 'protecting' the amine
and also adding a leaving group.
Unfortunately, this would require tosyl chloride, which isn't the easiest reagent to acquire, and Red-Al, while cheaper and safer than LAH, is less
commonly available to the amateur. However, if this could work in moderate yields, it might be worth the effort.
Is there anything I am missing here? I can't, off the top of my head, think of a way to halogenate the amino alcohol without some effect on the amine,
concentrated hydrohalic acids would result in the formation of an amine salt (perhaps still reducible?) and phosphorus halides/thionyl chloride will
react with the amine. Perhaps oxalic or cyanuric chloride?
 
[Edited on 24-8-2024 by Elemental Phosphorus]
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