[TheQuestion90]

I was given a problem in class and I cannot figure it out. Neither can my study group. Spend nearly 2 hours today in circles of retro-synthesis. Please *delete me*!!! I typed up the question parameters and drew the compound

[discodermolide]

OK, the Grignard is the final reaction or the first disconnection.
There are two choices here.
What disconnection(s) of the target leads to the Grignard reaction?

[Mishifus]

Hello, I am no synthesis expert but could something like this work?

I did not detail reagents, I'm too lazy for that 

-Mishi

[discodermolide]

Not really, you are adding triple bonds yet your products have double bonds.
Also a Grignard reagent from a tosylate and Mg is not likely to happen.

[Mishifus]

I am sorry about that, I guess it's pretty late for me!

I hope this is better

[discodermolide]

OK, your product is not the same as the one shown in the original question.
Grignards will not give ketones when treated with carboxylic acids. You need something else to do that reaction.

[discodermolide]

Here are two disconnection possibilities to get you started:

[Mishifus]

third attempt!

[kriggy]

What reagent are you going to use to get halogen derivate from carboxilic acid?

[Mishifus]

I'd guess the Hunsdiecker reaction:
http://en.wikipedia.org/wiki/Hunsdiecker_reaction

Bromine/chlorine and some silver (I) salt in CCl4

[discodermolide]

What's wrong with thionyl chloride?

[Nikola95]

EtOH  EtOTs

HC≡CH --LiNH2(1 eq.), NH3(l)-->HC≡C:^-

HC≡C:^- + EtOTs ----> Et-C≡CH ---Lindlar cat., H₂---> Et-C=CH2

Et-C=CH2 ----1.BH3, THF;--2.H2O2, NaOH, H2O---> BuOH

BuOH ----> BuMgCl

BuMgCl + MeCHO -1. THF--2.H+/H2O> Bu-CH(OH)-Me, reduce this to: Bu-CO-Me

React Bu-CO-Me with (1) from attached image to get product.

[kriggy]

I was reffering to the reaction pathway starting with benzyl alcohol

[discodermolide]

I was reffering to the reaction pathway starting with benzyl alcohol

Apologies

[kriggy]

I was reffering to the reaction pathway starting with benzyl alcohol

Apologies

Not needed but thanks 

One more question: Dont you need to protect the other carbon in acetylene when doing the coupling reaction? So you dont get acetylene substitued on both carbons.