[doverby18]

I need help with a synthesis problem in which acetylene is the starting material and 1,6 hexanediol is the ending material. I can't figure it out! Someone please *delete me*!!

[Gregorian]

Hi,
My guess would be: convert the ethyne ( acetylene) into an ethene using H2/Pt
Then use water to get a primary alcohol (ethanol)
Then use PCC to oxidize it into an aldehyde (PCC so it doesn't go all the way to carboxylic acid)
Then use Gringard to get an alcohol with the number of the carbons u need.
and then to add an OH to the terminal end, you use hydroboration oxidation
(i am not sure about this last step though)

[nj_bartel]

Hydrogenation reduces to alkane - you need either Lindlar's, dissolving metal reduction, or protodeborination to reduce to alkene.  You also can't use water to form an alcohol, at least not in the lab - you either do hydroboration/oxidation or oxymercuration/reduction.  Next, Grignard's are incompatible with alcohols - they quench the Grignard.

That aside, my advice would be to build up your carbon framework first (alkylation), then look into functionalization.  Work from there and post what you come up with.

[Gregorian]

Hydrogenation reduces to alkane - you need either Lindlar's, dissolving metal reduction, or protodeborination to reduce to alkene.  You also can't use water to form an alcohol, at least not in the lab - you either do hydroboration/oxidation or oxymercuration/reduction.  Next, Grignard's are incompatible with alcohols - they quench the Grignard.

That aside, my advice would be to build up your carbon framework first (alkylation), then look into functionalization.  Work from there and post what you come up with.

Yea you're right about the hydrogenation! I forgot my orgo already !!  I meant Lindlar

actually I learned that using water with alkenes gives alcohol

but we can summarize all these steps by using oxymurcuration or hydroboration to get the aldehyde like u said
Grignard won't be in contact with alcohol, but it will be in contact with aldehyde to elongate the carbon chain
but the problem is making the OH go to the terminal positions

I had another ideas in mind like using NaNH2 to remove a hydrogen from the ethyne (but then I don't know if it will remove two hydrogens... I dont think so though)
the we will have H-C(triple bond)C- and we use CH3-CH2-CH2-CH2-Br so that we get 1-hexyne
Then we do hydroboration to add OH to the terminal C on the triple bond , but then I don't know how to add the other OH to the other terminal carbon!

[nj_bartel]

You can make an alcohol from an alkene and water, by using H₃PO₄ at high pressure and ~250 ^oC, which is not reasonable for a lab procedure =P.  Sorry, mistook what you were saying about the Grignard - thought you were making it on an haloalkane with an alcohol.

Your second set of steps is what I was hinting at, but I think I was misguided.  Setting yourself up for a Suzuki/Stille Coupling might be the necessary route.

[kiwi]

Deprotonate one end of the acetylene with strong base, and then use the anion to open the epoxide ring of ethylene oxide, giving an alcohol with +2 carbons. Repeating with the other end (same pot) gives the required diol with an internal alkyne, which you can reduce down by hydrogenation. Way faster.

[nj_bartel]

Problem: if you treat that substance after the first alcohol with sodium amide again, you're going to be deprotonating the alcohol - is using a large quantity of sodium amide a solution to that?  Unfamiliar with that reaction.  And what's the proton source for the alcohol?  Do you form the 2 oxides, then treat with a weak acid?

[azmanam]

yes, excess base will work.  or you can protect as a silyl ether, open the 2nd epoxide and deprotect.  reprotonate with water.