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#1 2010-08-24 16:38:44

orgopete
Administrator

Cyclopentadiene synthesis scheme

Here is a problem that shows we can't all be prefect:

An  organic compound (A) of m.f. C5H6 reacted with ethyl magnesium iodide to give (B).(B) reacted with CO2 to give a salt which on hydrolysis gives (C).(C) when treated with DIBALH gives  (D).(B) reacted with HCHO and on further acidification  gives (E).(E) when oxidised with PCC gives (D).A basic solution  of (A) shows aromatic characters. Find (A) to (E)

This is the chemistry that is being suggested. Note that I put the product hoped for between C and D. DiBAL can be used to reduce an ester to an aldehyde, but not an acid. All that would happen is hydrogen would be evolved and a borate ester formed.

        http://www.curvedarrow.com/chem/ZZ7FE3A4DC.jpg

There is a second problem with this problem that I didn't address, namely conjugation. Since the starting material is cyclopentadiene and while the anion can be reacted, it is quite difficult to maintain the diene substitution pattern. Again, because cyclopentadiene is quite acidic, adding a carbonyl to it will increase the acidity. It would be very easy and preferred for the double bonds to be in conjugation with the carbonyl group. However, since there is the prior error and it doesn't really seem to address the conjugation-deconjugation, I left it as is. I would very much doubt those would be the products (except possibly for an extremely skilled chemist).

[cyclopenta-2,4-dienecarboxylic acid, cyclopenta-2,4-dienecarbaldehyde, cyclopenta-2,4-dien-1-ylmethanol]

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