Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: mpv on March 05, 2012, 04:44:59 AM

Title: Problem
Post by: mpv on March 05, 2012, 04:44:59 AM

Hope you'll enjoy this one ... Propose a mechanism for the following reaction.

Title: Re: Problem
Post by: Dan on March 05, 2012, 05:32:54 AM

Is it thermally or photochemically induced?

Title: Re: Problem
Post by: mpv on March 05, 2012, 05:42:43 AM

photochemically

Title: Re: Problem
Post by: mpv on March 06, 2012, 01:53:02 PM

No takers... probably it's to easy for you guys.

Title: Re: Problem
Post by: BobfromNC on March 06, 2012, 02:52:16 PM

Here's my mechanism, a 2+2+2+2 to make a very sterically hindered intermediate, followed by a Cope rearrangement.   The intermediate may not exist for any detectable time.  Do I get a Scoobie snack?

Title: Re: Problem
Post by: mpv on March 06, 2012, 03:09:13 PM

Well you're not very far, but the dicyclopropane intermediate is very unlikely to form. Try thinking some classic photochemical reactions (Hint: only the cis form gives the final product).

Title: Re: Problem
Post by: BobfromNC on March 06, 2012, 04:21:53 PM

Do they propose that the 2 dienes each do a [2+2] reaction to form two cyclobutane rings and then those react/rearrange?  That also works for me, but still is a series of concerted reactions. 

Title: Re: Problem
Post by: mpv on March 06, 2012, 04:41:57 PM

It's even more interesting, only one does a 2+2

Title: Re: Problem
Post by: Arctic-Nation on March 10, 2012, 12:23:11 PM

If that's a first step, is the second an intramolecular Diels-Alder?

Title: Re: Problem
Post by: mpv on March 10, 2012, 03:20:39 PM

Bingo. Can you propose a full mechanism.

Title: Re: Problem
Post by: Arctic-Nation on March 11, 2012, 02:21:35 PM

Well, I've attached the mechanism I found, but I haven't checked whether Woodward-Hoffman agree with it or not. Everything looks awfully constrained, and I've never been good at electrocyclic reactions.