[earbmu]

Hi everyone!

I was trying to do this reaction, but couldn't pass the Michael addition intermediate. The problem asks to use Robinson annulation reaction to synthesize this compound.



My buddy said you do an intramolecular aldol, followed by dehydration, but I can't see how that works. Can someone help me with the drawing of the intermediate steps.

[refid]

I think its a cyclic beta-diketo-ester + alpha-beta unsaturated pentenone,





*edit: image ketone in wrong place

[english]

I believe there's a much simpler way to go about this, but the best way in my opinion is to work backwards.

You have the Robinson annulation mechanism worked out in your textbook no?

For a start, the double bond tells you where the OH group was before elimination (E1cb elimination).

(Remember that only alpha-hydrogens are sufficiently acidic to take part in elimination reactions, or deprotonations for that matter.  This means that your OH group before elimination will be in the beta position relative to your C=O group.)


redif is correct, other than his small mistake of putting an Et group of the ester instead of a Me group as suggested in the original compound.


Just to show you an alternate method, I will display how I went about doing this (not the easiest way, but it explains a lot of things).  Notice how I've separated the annulated product into two separate reactants of interest; your enone, or unsaturated ketone, and your ketone with a rather acidic hydrogen being flanked by a ketone and ester.

[Custos]

I think its a cyclic beta-diketo-ester + alpha-beta unsaturated pentenone,

The ketone on the initial cyclohexanone ring is in the wrong place - it needs to be next to the carboethoxy group.

[refid]

I think its a cyclic beta-diketo-ester + alpha-beta unsaturated pentenone,

The ketone on the initial cyclohexanone ring is in the wrong place - it needs to be next to the carboethoxy group.

fixed the problem, thanks for noticing

[earbmu]

Got it. Thank you all for your help