retro-aldol_mech_handout(1)

retro-aldol_mech_handout(1) - Aldol and Retro-aldol...

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The following transformation involves one retro-aldol reaction followed by one aldol reaction. Draw a curly-arrow mechanism. O KOH O As discussed in class, an α , β -unsaturated carbonyl is related by hydration to a β -hydroxycarbonyl ( NOT α - hydroxycarbonyl, for reasons that will be clear when we push the curly arrows) Solution β α O 3 2 1 O Aldol and Retro-aldol Mechanisms Colin Lam, Chem 30C, Winter 2012 H OH NOT 3 2 1 O OH H In this question, an α , β -unsaturated carbonyl is converted to another α , β -unsaturated carbonyl with a dramatic change in the carbon skeleton. Don't panic! You're given only KOH, which is a base and nucleophile, as the only reagent. How will it react with our α , β -unsaturated carbonyl? Was the following reaction the Frst thing you came up with? (Hopefully you remember something from 30B!) Aim to master the curly-arrow mechanisms for both the forward aldol (including the elimination of H 2 O) and the retro- aldol (including the conjugate addition of H 2 O) reactions. If you do, you will be able to spot the correct C–C bond to disconnect and aldol retrosyntheses will be much more tractable.
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retro-aldol_mech_handout(1) - Aldol and Retro-aldol...

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