[willfitz]

This is a 3rd year chemistry question, but I couldn't get any answers in the undergraduate forum, so I am asking here instead.

I am to devise a step by step synthesis of the fly phermone olean from 1,3-dithiane and 4-bromo-1-butene (diagrams attached).

I'm really not sure where to start. I have an idea of attaching the alkyl groups from the butene to the dithiane and replacing the dithiane with a carbonyl, but I can't understand how to get both oxygens onto that same methylene carbon.

Any help would be highly appreciated.

[Dan]

I have an idea of attaching the alkyl groups from the butene to the dithiane and replacing the dithiane with a carbonyl, but I can't understand how to get both oxygens onto that same methylene carbon.

Good start, you're on the right track. The functional group present in that pheromone is an acetal. How are acetals made?

[willfitz]

Good start, you're on the right track. The functional group present in that pheromone is an acetal. How are acetals made?

So, I can attach the carbon chains to the dithiane, then replace the dithiane with a ketone... theoretically, if I could make the end of the chains an alcohol, I should be able to make an acetal using acid, right? The only problem I see is that hydration of the alkene would, if I understand correctly, be more likely to put the alcohol on the 2-carbon rather than the 1-carbon...

[Dan]

theoretically, if I could make the end of the chains an alcohol, I should be able to make an acetal using acid, right?

Good! Almost there!

The only problem I see is that hydration of the alkene would, if I understand correctly, be more likely to put the alcohol on the 2-carbon rather than the 1-carbon...

There are several ways to hydrate alkenes. Acid catalysed addition of water across a double bond will give the undesired regioselectivity (Markovnikov addition) as you rightly say. Do you know any other ways of hydrating a double bond (more than one step may be required)? Think about anti-Markovnikov addition reactions...

[willfitz]

There are several ways to hydrate alkenes. Acid catalysed addition of water across a double bond will give the undesired regioselectivity (Markovnikov addition) as you rightly say. Do you know any other ways of hydrating a double bond (more than one step may be required)? Think about anti-Markovnikov addition reactions...

OK, hydroboration looks good. Thanks very much!