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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: mrsandman on February 25, 2009, 07:57:24 PM

Title: Mechanism for removal of tboc group by tfa
Post by: mrsandman on February 25, 2009, 07:57:24 PM

I have a question about deprotecting tboc group with tfa

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg3.imageshack.us%2Fimg3%2F9397%2Ftfaremovaloftboc.jpg&hash=b9f968b7548d5066ee54a76059088a97983dddac)

I'm thinking that the Nitrogen will attack the carbonyl on TFA and form a tetrahedral intermediate.  Then the OH on TFA would be in proximity to the the carbonyl to the amide and that would attack and you would have like a cyclobutane like structure and the lone pairs would come down and in the end you woud have the tboc group attached to the tfa + the deprotected molecule.

Title: Re: Mechanism for removal of tboc group by tfa
Post by: mrsandman on February 25, 2009, 11:49:14 PM

nvm got it

Title: Re: Mechanism for removal of tboc group by tfa
Post by: expert on February 26, 2009, 12:26:41 AM

I don't know what you've found. Please share with us. I'm sure TFA protonates carbonyl group in CO(OBu-t) and the positive charge moves to t_Bu group that among alkyls stabilizes the positive charge the best. t_Bu+ cleaved from the molecule and gets quenched by any nucleophile available around, even if it'd CF3COO-. Obviously, CO2 released at the next stage.

Title: Re: Mechanism for removal of tboc group by tfa
Post by: Dynamic on February 26, 2009, 08:43:40 PM

Did you get isobutene as one of your products?

Title: Re: Mechanism for removal of tboc group by tfa
Post by: expert on February 27, 2009, 01:08:06 AM

You do, by loosing proton from Me3C+, if no good nucleophiles around.

Title: Re: Mechanism for removal of tboc group by tfa
Post by: ruler9 on November 06, 2009, 08:56:08 PM

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fc%2Fc5%2FTBOC_deprotection_scheme.png&hash=eddb2bbbca6b76e5b4e6b90b13ac1622e9fc569a)

Title: Re: Mechanism for removal of tboc group by tfa
Post by: movies on November 07, 2009, 02:19:17 PM

Is the nitrogen of an amide the most basic part?  How would that change the mechanism you drew?