[azmanam]

Yes, R groups can be hydrogen

Grignard reagents react twice with acid chlorides and other carboxylic acid derivatives to give tertiary alcohols not ketones.

I like your 3 four carbon chain ideas.  My 3 four carbon chains includes an alkyl chloride like your third piece, but not an acid chloride (for the reasons above).  My third one has a terminal alkyne, not a terminal vinyl chloride. 

[bessieboy521]

Im am going to try and build these chains in a way that they can be put together... What was your third one if i may ask? just an aldehyde?
Also, do think there could be a use of LDA anywhere??? Deprotonating an alpha carbon and throwing on a chain there?? I haven't really thought it through at all, just throwing it in the mix.

[azmanam]

Yes, mine was an aldehyde.  Yes LDA deprotonates alpha carbons.  I didn't use it, but I can think of a way to make this molecule that would use it.

[bessieboy521]

OK so i took the four pieces you suggested, and Attached them like so, I figure since the oxygen is already deprotonated, the basic Sodium solution wouldn't really an effect. Does this look good, or have i doing something illegal so far... I am going to try and build the four pieces now, with the assumption that this synthesis is legal so far.

EDIT: Replaced the graphic with the correct reagents... I can accept messing up the Na NH3 reagent, as its a bit confusing, But wow messing up on the oxidant by putting a reduction reagent in is unacceptable.

[azmanam]

This is the synthesis I envisioned, but some of your reagents are incorrect (the transformation is correct, but the reagent you used to carry out the transformation is incorrect).

Recheck: NaBH4, and the final use of NaNH2

Good work so far

[bessieboy521]

OK so if you check my last post, I made the correcting in the post... Here is my retro of the starting 4 carbon chains. Everything leads back to Ethyne. I certainly hope this is acceptable, and please let me know if you see anything wrong!! I'd be most appreciative. I thank you a lot for you assistance this far as well!

[azmanam]

seems good to me.  Well done.  2 comments.  That's not the intermediates in the LDA alkylation (although you do get that product).  You need a different bromination in converting 1-butanol into 1-bromobutane bottom middle.  If you use HBr, your molecule will rearrange to give 2-bromobutane.

Else ok.

PS don't forget water in your mercury sulfate/H2SO4 hydration of an alkyne to an aldehyde.

[bessieboy521]

I accidentally put the theoretical charges backward. Hopefully there is not issue with PBr3.... and alas, I forgot to put in the water. How did you catch all three mistakes that fast! Thanks a LOT!! Hopefully this will be the last image post! This is the retrosynthesis/synthesis of (E)-5-propylnon-3-en-5-ol using Ethyne as the only source of Carbon in the molecule.

I thank you for the *delete me* Hopefully any onlookers can get something out of the process and understand Alkyne chemistry a bit better as well!

EDIT: NOTE: I forgot the water in the first reaction with Sulfuric Acid... AGAIN.

[azmanam]

Thanks for your kind words.  I teach college organic chemistry.  Grading quickly is what I do . [1] 

That's still not how LDA works.  You deprotonated the alpha carbon correctly, but the alkyl bromide does not ionize to the carbocation.  Even if it did, it wouldn't ionize to give a primary carbocation.  Even if it did, your carbocation has 3 carbon atoms in it and it should have 2   The enolate does an S_N2 displacement of the bromide directly.

Let's go ahead and put H3O+ before the Na/NH3 alkyne reduction in the last step.  This is how you would do it in real life in lab.  You're right the alkoxide is not incompatible with the reagents, but having H3O+ before the reduction is the most technically correct way to do it.

And, if you want to get picky, watch your bond angles around your alkyne in your 3rd-to-last compound.

Well done overall.  You worked hard and made a lot of progress in one day

[1] incidentally, I just blogged about this today
http://www.chemistry-blog.com/2011/05/12/the-other-side-of-the-lectern-a-reflection-on-my-first-year-of-teaching-undergrads/

[azmanam]

The way I initially though to make the pieces:

acetylene --[Na/NH₃]--> ethylene --[HBr]--> ethyl bromide --[sodium acetylide]--> 1-butyne



1-butyne --[i. BH₃ ii. H₂O₂/NaOH]--> butanal

1-butyne --[Na/NH₃]--> 1-butene --[i. BH₃ ii. H₂O₂/NaOH]--> 1-butanol --[PBr₃]--> 1-bromobutane

1-butyne --[NaNH₂]--> (carbanion of 1-butyne, CH₃CH₂CΞCNa)

Once here, my endgame was the same as yours.  Neither way is better or worse.  They're both full credit answers

[bessieboy521]

The reactions in parenthesis are not real charges... in my way of learning retro, I put a fake molecule with unreal charges up after breaking a bond, and then try and find reagents that would allow them to behave as if they really had the charges, but i do know that the H is removed leaving a resonance stabilized charge, however the Bromine is displaced through Sn2. I will fix the alkyne bond angle, which should obviously be 180 degrees... (I'd throw a fit to have points taken off for that however.) I will as well as the pronation step, since in a lab i would have to isolate most of the products in each step.

Later tonight, I am going to post the other two retro problems in a new thread for debugging purposes. Again, I thank you a ton for your quick responses and nudges in the correct direction.