[Annonymous]

Hello!  I have two questions:

1.  Could someone please help me determine the steps of synthesizing trans-2,3-Butanediol from 2-butyne.  I was initially thinking of 1. mercuration 2. acidify the lone ketone 3. Then I'm lost. 

2.  Does the following reaction prefer SN1 or SN2 and why?

2-Butanol + HBR -----> 2-bromobutane

I found a similar post on this forum, but no clear cut reason was formed.    http://www.chemicalforums.com/index.php?topic=37973.0

Thank you!

[Honclbrif]

Know of any reactions that specifically make diols? How would you get from an alkyne to the starting material for that reaction?

[nox]

Redraw your butanediol such that it sits in a conformation that has both OH groups cis to each other. The answer come to you right away.

[Annonymous]

Nox,

I know how to synthesize a cis-2,3-butanediol.  However, for this assignment, I have to make a trans-2,3-butanediol.  Is there any reaction where I can do this in one step?  I'm pretty sure there isn't.  I didn't know if there was a way to complete the reaction in multiple steps.  Any ideas?

Thanks!

[Honclbrif]

If dihydroxylated, which substrate would yield the cis-diol?

Therefore, how would you have to alter the geometry of the substrate to get the trans-diol?

You can go directly from the alkyne to either substrate in one step.

[nox]

Nox,

I know how to synthesize a cis-2,3-butanediol.  However, for this assignment, I have to make a trans-2,3-butanediol.  Is there any reaction where I can do this in one step?  I'm pretty sure there isn't.  I didn't know if there was a way to complete the reaction in multiple steps.  Any ideas?

Thanks!

No, I'm saying start with trans diol, presumably drawn in an extended conformation. Then see which bonds you can rotate to put the 2 OH groups cis to each other. Once you have done that, the answer should become quite obvious.