Week 3: Rerunning reactions from Week 2 and finalizing synthesis of the diketopiperazine

The elimination, isomerization, and Diels Alder reaction from last week did not progress as expected. After workup, 1H NMR analysis showed many different impurities with very little product formed. This could be attributed to remaining impurities in my starting material, resulting from ineffective purification of previous reactions.

Therefore, I went back to square one and reran the aldol condensation of DKP and phenylacetaldehyde. This reaction went much better than the first time I attempted it, and so I continued with the acetylation without further purification. This time, I used acetic anhydride, triethylamine, and DMAP (catalyst). After 3 hours, I spotted the reaction mixture with reference to the starting material. A new spot was present in the reaction mixture with a much higher RF value, suggesting the reaction was carried out to completion. After workup, the 1H NMR spectrum showed a peak shift further downfield that was not present in the starting material, confirming completion. Since this 1H NMR spectrum showed very little impurities, I carried out the elimination, isomerization, and Diels Alder reaction. This worked surprisingly well with a 60% yield after purification.

Next week, I will use Ring Opening Metathesis Polymerization to polymerize this product using Hoveyda Grubbs II catalyst in THF (Scheme 1).

Blog 3 Scheme 1

Additionally, this week I have successfully completed the synthesis of DKP 3 by performing a Staudinger reduction (Scheme 2). I will now have enough DKP to focus on optimizing the reactions leading to the finalized monomer.

Blog 3 Scheme 2 Pic

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