Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: thescepticalchymist on April 17, 2018, 12:14:00 PM
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My professor gave us this sheet (https://i.imgur.com/SAbPCX5.jpg) to work on yesterday.
I'm pretty confident about my ranking of the acidity of the compounds, and I think I'm right about the aldol condensation mechanism -- please correct me if there are mistakes!
On the other hand, I'm not sure where to start with #2. It looks like an aldol cyclization, since the product has the alkene and the C=O in conjugation, but I am not 100% sure about what the starting material or the mechanism would be. I at least know that the starting material is going to be a chain containing two enolizable carbonyl groups, but I need to know the correct answer because my prof. is definitely going to quiz us on this next class.
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1). If you have acidic conditions, you don’t need the base B:, erase it immediately, because it is a serious mistake. Just continue by drawing an acidic dehydration and that’s all.
2). Try a retro-synthesis and go back:
2-Cyclohexenone ← 3-hydroxy-cyclohexanone ← ? (= a six member aliphatic aldehyde containing a ketone group at the end.)
3). Ignore the methoxide catalysis for the moment. But for your own and further information, this reaction involves a cyclization step that has a higher activation energy and therefore, strong catalysis is needed. On the other hand, strong basic conditions avoid the simultaneous double aldolization of a ketone by an aldehyde, contrary to strong acidic conditions that favor it.
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I'll assume that you know what an elimination reaction is. What functional groups can be eliminated to turn to alkenes? Where would that functional group be placed in on that ring?