[AlphaScent]

I was proposed a question from a friend of mine about how a reaction would proceed.  I have an idea but have never seen some of the conditions.

The question is:

1-Heptyne is reacted with:

1) Lithium dimehtylcuprate (Gilman reagent); N-bromosuccinimide (NBS)
2) Mg (gound state metal), Acetonitrile, H3O+
3) Dilithium dimethylcyano cuprate (Modified Gilman)

For the first set of conditions my initial thought was the Gilman reagent would have to react the acidic proton of the terminal alkyne.  But I feel that I am missing something and it is possible to alkylate this compound.  I have read that Gilman reagents can reduce internal alkynes to cis alkenes.  Can it do the same for terminal.  Is the product a terminal alkene and then allylic bromination with NBS?  That makes some sense.

For the second reaction it has to be a grignard and then addition of the grignard to acetonitrile followed by acidic work-up to produce the ketone.

The last reaction is where I am stumped.  Gilman reagents add via 1,4-conjugate addition.  This is done though with alpha beta unsaturated ketones (allylic ketones).  Here it will be a homo allylic moiety. 

All answers are appreciated!

Cheers!

[orgopete]

Okay, I didn't know either. I had to look this up. Gilman reagents will add to terminal acetylenes. NBS will convert the cuprate to a bromide, Mg to Grignard, acetonitrile to conjugated ketone, and second Gilman to conjugate addition. Good question.

[AlphaScent]

Thanks Orgopete.

So my initial gut feeling was correct.  It will abstract the proton producing a cuprate complex and the NBS/cuprate will allow the bromine to add to the terminal acetylene.  This is cool chemistry, im sure it is oxidative addition and not Sn2 with this particular cuprate.  So cool. 

If you could tell me or direct me to where you found the details on acetylenic cuprates and the NBS that would be swell.  Thanks again

Cheers!

[Dan]

Thanks Orgopete.

So my initial gut feeling was correct.  It will abstract the proton producing a cuprate complex

No, that's not what Orgopete said. You will get carbocupration of the triple bond.

See: http://en.wikipedia.org/wiki/Reactions_of_organocopper_reagents#Stoichiometric_Reactions_of_Organocopper_Compounds

[AlphaScent]

Dan,

Ok, I was wrong it is not extraction at all.  Insertion of the lithium dimethylcuprate to the terminal triple bond forming carbocupration.  I attached a scheme of what I have to understand the reaction scheme to look like.  I was told not to attach pdf so I did png.

[orgopete]

Almost. The Gilman donated a methyl group at one end and a copper at the other. The copper becomes the bromine and the rest as shown.