Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: SinkingTako on April 24, 2014, 09:51:49 AM

Title: Practice problem 4
Post by: SinkingTako on April 24, 2014, 09:51:49 AM

See attached, and propose a mechanism. Hint: it involves a Claisen rearrangement.

Title: Re: Practice problem 4
Post by: Rutherford on April 24, 2014, 11:36:06 AM

This:

Title: Re: Practice problem 4
Post by: SinkingTako on April 24, 2014, 11:49:26 AM

Hmm, close, but looks slightly weird. How did you form your R-OTs in the first step from the alcohol? (I mean is it favoured over other reactions with an acid?) I think the rearrangement shouldn't have involved the Ts.

Title: Re: Practice problem 4
Post by: SinkingTako on April 24, 2014, 11:56:45 AM

And on a side note TsOH, MsOH, TfOH should all be non-nucleophilic.

Title: Re: Practice problem 4
Post by: Rutherford on April 24, 2014, 12:34:23 PM

Oh I've mistaken TsOH for TsCl.

Title: Re: Practice problem 4
Post by: Rutherford on April 26, 2014, 12:32:07 PM

If no one answers soon, you could give an additional hint.

Title: Re: Practice problem 4
Post by: SinkingTako on April 26, 2014, 12:53:56 PM

Okay, see below for the first step. After this should be the formation of a regular claisen enol-ether.

Title: Re: Practice problem 4
Post by: Rutherford on April 30, 2014, 12:06:22 PM

Okay, OH group gets protonated and eliminated. Then this rearrangement happens:
Right?

Title: Re: Practice problem 4
Post by: SinkingTako on April 30, 2014, 12:52:18 PM

Yeap yeap yeap! This is correct! *clap clap* Your turn to post a question!

But I think it is slightly more correct to draw the arrow going in the other direction (ie anti-clockwise instead of clockwise), because usually it's the alpha carbon that is nucleophilic. Though since it's pericyclic doesn't actually matter that much.

Sigh I really hope that this problem thing can last. People lurking in this forum respond please?

Title: Re: Practice problem 4
Post by: Rutherford on April 30, 2014, 01:23:55 PM

After your hint it was pretty obvious (you even said that it is Claisen afterwards). I waited for someone else to answer, but nothing.