[azmanam]

This time, I'm not going to answer after every guess.  The community can discuss and combine and come back with a consensus answer.  I like that better than the 'is this right?' 'no.' 'how bout this?' 'sorta, think about it this way.' ... approach to problems.  So discuss and argue and debate amongst yourselves and let me know when you think you've got the answer.

QUESTION: Provide a complete, arrow pushing mechanism for the following transformation and predict the product:

[Heory]

No stereoselectivity in the reaction?

[Heory]

I prefer the old way of discussing, for few people are willing to post their viewpoints.

[azmanam]

It looks like you're right, no one wants to play my way.  Oh well.

There will be stereoselectivity issues to discuss later, but first we'll focus on just the arrow pushing.  You have chosen the wrong nucleophile after L.A. activation, and as a result, the rest of the mechanism is off track.  Reassess with a different nucleophile and see what else looks interesting.

[Dan]

This one's tough. I got to a tricyclic intermediate but I'm not sure where to go from there, or even whether I'm in the right place anyway...

[azmanam]

Diels Alder.  Interesting, but no.  (plus, I think the bottom face opposite the isopropyl group would be more accessible if that were to occur )

[nj_bartel]

For the first mechanism proposed - are there any mechanisms involving vinylic carbocations that are generally accepted?

[azmanam]

addition of HX to alkynes

http://www.chemistry.ccsu.edu/glagovich/teaching/311/content/alkyne/reactions/alkynerxn2.html

[Heory]

 

[Heory]

I'm really very sorry. Your drawing always looks rather beautiful and I just want mine to be better. Well, I will use the ACS style.

[nj_bartel]

addition of HX to alkynes

http://www.chemistry.ccsu.edu/glagovich/teaching/311/content/alkyne/reactions/alkynerxn2.html

Ah alright.  When I took organic I, that mechanism was presented to me as still pretty widely disputed due to the instability of that cation.  An alternative possibility presented was an X'onium intermediate.

Edit:  I like your new one Heory.

[azmanam]

I had no idea this question would be this intriguing.  Three completely different guesses with three completely different modes of activity, yet none of them get to the product of the reaction.  Very fun

Perhaps it would be useful to think about and list in words what the various functionalities of the two reagents are.  Then maybe try to think about how they might react with each other under lewis acidic conditions.  Look for best nucleophiles, best electrophiles and see if we can talk through it that way?

Heory: not sure what you're talking about.  Your schemes are nice and quite easy to follow.  Keep up the good work. (btw, I don't use ACS, I use TotSyn style, downloaded from here:  http://totallysynthetic.com/blog/?page_id=287)

[Heory]

I am totally confused...
OH is not a good nuleophilic reagent in the presence of LA
i need more clues
now it is 0:30 here and i must go to sleep
see you tomorrow

[azmanam]

  see you tomorrow.  Let visions of terpenes dance in your dreams

[Dan]

Diels Alder.  Interesting, but no.  (plus, I think the bottom face opposite the isopropyl group would be more accessible if that were to occur )

My structure also breaks Bredt's rule... Schoolboy error...

This is tough, I need more time to think about it. I'm liking Heory's diene nucleophile though.