[xoggyux]

Hi,
I am stuck with this problem.
How to synthesize 1-methyl-1bromocyclohexane from cyclohexene?
I think that the methyl group could be added with a Me^-+Li complex however to have both Br and Me in the same carbon I would need a germinal halide right? I do not think I know how to make a germinal halide. Any insight?

[xoggyux]

I just thought of this:
cyclohexene ---(Br₂) --> vicinal 1,2 dibromide
1,2 bromocyclohexane ---(KOH)---> cycloalkyne (this is weird, in the whole book there is no mention of their existence but I did some searches and it seem they exist indeed)
cycloalkyne ---(excess HBr)---> geminal (1,1)-dibromocyclohexane
(1,1)dibromocyclohexane ---(1 equivalence of Me^+-Li)--> 1-methyl-1-bromocyclohexane.

Is this correct?
Also since the book does not mention cycloalkynes whatsoever I believe there must be an alternative way (thats assuming my reasoning was correct) to synthesize the molecule. Thanks.

[Squirmy]

You've recognized that you need to make a C-C bond. What kind of reactions have you learned that make a C-C bond?

[xoggyux]

You've recognized that you need to make a C-C bond. What kind of reactions have you learned that make a C-C bond?

Well I infer from your question that you believe my former proposition was incorrect.
So far these are the methods we have studied that can form C-C bonds:

• Reaction of an acetylide ion with an Alkyl Halide or Sulfonate ester.
• Diels-Alder (I ruled this one out since I already have a whole ring?)
• Grignard reagent and organometallic compounds (so far this one looks the more promising.)
• Reaction of a cyanide ion with an Alkyl Halide or Sulfonate Ester.

[aldoxime_amine]

• Grignard reagent and organometallic compounds (so far this one looks the more promising.)

How do you use that one?

[xoggyux]

• Grignard reagent and organometallic compounds (so far this one looks the more promising.)

How do you use that one?

I could use Me^+-Li to add to an sp3 carbon that is attached to two Br(s) (geminal dibromide)?

[aldoxime_amine]

How does it work on a ketone or aldehyde?

[xoggyux]

How does it work on a ketone or aldehyde?

Uhm... I am lost  the book presents briefly a couple of very simple examples (none of which is ketone or aldehyde, in fact not even cyclic molecules).
Because of your insight I tried to do it myself and if I get a cyclohexanone to react with 1 equivalence of LiMe I believe the end result would be a 1-methyl-1-cyclohexanol (deprotonated, e.g. O^- instead of OH) which then it could be protonated (twice) protonated with H⁺ and then add HBr to replace the OH group for a Br group.

But if that were to be the case then I am back to square one since the only reaction I know to get a ketone is addition of H₂O to an alkyne (and if I get an alkyne I think then the best path for the reaction is the one I proposed before, or it isent?)

[aldoxime_amine]

Because of your insight I tried to do it myself and if I get a cyclohexanone to react with 1 equivalence of LiMe I believe the end result would be a 1-methyl-1-cyclohexanol (deprotonated, e.g. O^- instead of OH) which then it could be protonated (twice) protonated with H⁺ and then add HBr to replace the OH group for a Br group.

Yes!! That is what I wanted you to think of.

Now, are you aware of methods wherein an alcohol is oxidised to an aldehyde/ketone?

[xoggyux]

Because of your insight I tried to do it myself and if I get a cyclohexanone to react with 1 equivalence of LiMe I believe the end result would be a 1-methyl-1-cyclohexanol (deprotonated, e.g. O^- instead of OH) which then it could be protonated (twice) protonated with H⁺ and then add HBr to replace the OH group for a Br group.

Yes!! That is what I wanted you to think of.

Now, are you aware of methods wherein an alcohol is oxidised to an aldehyde/ketone?

alcohol ---(CrO₃ , H₂SO₄)--> Ketone

So let me see if I got this straight:
Alkene ---(HBr)---> bromocyclohexane
bromocyclohexane---(OH^-)--->cyclohexanol
cyclohexanol---(CrO₃, H₂SO₄)---> cyclohexanone
cyclohexanone---(Me^+-Li) ---> 1-methyl-1-hexanol (deprotonated)
1-methyl-1-hexanol (deprotonated)---(H⁺)---> 1-methyl-1-hexanol
1-methyl-1-hexanol---(HBr)---> (1)-methyl-1-bromocyclohexane


It looks good to me
Is it correct?

[Squirmy]

You can go straight from cyclohexene to cyclohexanol. Do you know of any reactions that can add water (H & OH) across a double bond?

Otherwise, it looks great!

[xoggyux]

Oh right, how could I miss that one. Acid catalyzed addition of water. 

Alkene ---(H₂O, H₂SO₄)--> cyclohexanol
cyclohexanol---(CrO3, H2SO4)---> cyclohexanone
cyclohexanone---(Me+-Li) ---> 1-methyl-1-hexanol (deprotonated)
1-methyl-1-hexanol (deprotonated)---(H+)---> 1-methyl-1-hexanol
1-methyl-1-hexanol---(HBr)---> (1)-methyl-1-bromocyclohexane

[aldoxime_amine]

yea!!

[xoggyux]

thanks for your *delete me*

[xoggyux]

thanks for your *delete me*

What that means? I intended to write "thanks for your help" why did help got censored?