Organic Chemistry Retro synthesis Problem.?
Hi. I was wondering if I am using the right reagents for this retrosynthesis problem. Beginning compound: methylcyclohexanol. End compound: Cyclohexane with methyl group at the 1 position, and trans to a OCH2CH3 on the 2 Carbon.
Here's what I was thinking:
1. I dehydrated the -OH to an create methylcyclohexene.
2. I added KMnO4 in the presence of cold, dilute HCl to create a syn 1,2 diol. (both alcohols are trans to the methyl group).
3. I added CH3CH2OH to the solution in hopes of creating the adequate ether.
And now, I am stuck. how do I get rid of the OH on the 1-Carbon. It is attached to a tertiary carbon.
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The solution is much simpler than that,
So you have formed the alkene, which is the first step. Now all you do is a hyrdroboration reaction to give the trans methyl ,-OH product. (B2H6/ H202 and H2O...remember that this is an anti-markovnikov addition and so the hydroxyl group goes to the least substituted position). Then simply react the alcohol to form the ether. (Na then CH3CH2X)
Stacey is correct
Not to pick on you, but your step 3 is wrong. The formation of the ether with an acid catalyst isn't going to be stereospecific. It could add to both or it could add to the wrong alcohol in the diol. Either way, a step with multiple products is generally wrong in a classic retrosynethetic analysis.
That being said, the final step would probably be a Barton-McCombie deoxygenation, to convert the OH into an H
I wish I could draw the structure of the molecule for you but 6-hepten-2-ol is CH2=CHCH2CH2CH2CH(OH)CH3 You would protonate the double bond first--this would be more favorable on C7 because it would provide the more stable 2 ° carbocation. The OH group would attack this carbocation OR the protonated double bond at C6 giving a 6-membered cyclic ring--a tetrahydropyran. So the product is 1,5-dimethyl tetrahydropyran. (Please check for the correct nomenclature--but I think you get the picture--this is intramolecular cyclization catalyzed by H+) You have the possibility of cis/trans isomerism--the two methyl groups can be on the same side--cis, in which case the molecule is achiral. OR you can have the Me's on opposite sides, in which case the molecule is chiral The cis isomer should be favored because both the Me's would be equatorial in the stablest configuration. In the trans isomer, the Me's are on each side--so if one is equatorial, another must be axial---less stable. So the most stable product is cis-1,5-dimethyltetrahydropyran Please inform me if I am correct I think your reaction would be a lot cleaner if you used Hg(OAc)2, etc instead of sulfuric acid Please lookup Baldwins rules for cyclization for a more in depth discussion The ether is simply an aprotic solvent--it does not participate in the reaction