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-   -   selective trimethylsilylation of hydroxy group in presence of amine (http://www.molecularstation.com/forum/chemistry-forum/44943-selective-trimethylsilylation-hydroxy-group-presence-amine.html)

Glenn 02-25-2004 04:25 AM

selective trimethylsilylation of hydroxy group in presence of amine
 
I am looking for a method to selectively protect the hydroxyl group on
an amino alchol that is easy to remove in subsequent step. I am
thinking trimethylsilyl protection would be a good idea. I tried
bis(trimethylsilyl)acetamide by dissolving the amino alcohol in THF
followed by dropwise addition of 1 equivalent
bis(trimethylsilyl)acetamide at room temperature, stirring 1 hour,
evaporate THF, add hexane, filter acetamide byproduct according to
literature procedure (JOC). This did not lead to clean product so I
redissolved in Ether, washed with water, sat'd NaCl, dried Ether
extract over sodium sulfate, evaporated ether to give product. The
literature reference did not characterize their product by nmr. nmr
analysis of my product indicated presence of 2 TMS groups. I thought
aqueous workup would remove any potential TMS from amine. My next try
will be trimethylsilyl imidazole which according to literature
selectively silylates alcohols in presence of amine.

Any further advice would be appreciated from others with similar
experience.

Thanks,
Glenn
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Mark Tarka 02-26-2004 02:27 AM

selective trimethylsilylation of hydroxy group in presence of amine
 
[Only registered and activated users can see links. Click Here To Register...] (Glenn) wrote in message news:<a2b5b5d1.0402242025.ae968ba@posting.google.c om>...
[snip...]

Not attempting to be brutal, but, which
amino alcohol?


Mark (...and which isomer?)

Muhammar 02-26-2004 02:42 AM

selective trimethylsilylation of hydroxy group in presence of amine
 
Yeah, life is full of adversities. Dissolve your material in methanol,
add few drops of aqueous ammonia or NEt3 and your silyl amine should
deprotect at room temp. The alternative is to add 0.95 eq. of acid
like HCl in ether, just enough to protonate the amine.

Since TLC destroys your compound, you can use NMR to see the reaaction
progressing. (In deuterated methanol).

By the way, what is wrong with TMS-Cl/NEt3 mix in DCM or MeCN for
silylation? Your work-up will be so much easier than with BSA.

[Only registered and activated users can see links. Click Here To Register...] (Glenn) wrote in message news:<a2b5b5d1.0402242025.ae968ba@posting.google.c om>...


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