Week 6: Primary Reactions and Optimizing Yields

The focus of this week was to optimize the original reactions, using all previous runs and yields to determine the reaction conditions. The first dibal reduction was run with standard conditions in dichloromethane. This reaction gave a 50% yield of the desired aldehyde which was higher than previous trials. The TLC taken while the reaction was running was difficult to read because both the starting material and product have limited UV activity and do not stain well on the plates. However, enough product was made to move forward with the aldol condensation. Since the starting material will not react with the next reaction, the product was not purified

The next steps in this reaction procedure were only slightly modified. For the aldol condensation, the reaction was run in DMF with cesium carbonate and stirred for 3 hours under nitrogen gas. This produces both isomers of the desired product but this run produced more of the clean desired isomer than previous runs. The sequential pyrrole condensation was run without quinoline and it ran with a 55% yield of product. This produced a decent amount of the core structure to move forward with. After all the runs of this three-step sequence over the summer, I had a total of about 250 mg of the product to work with. This will be used in the following 3 weeks in new reactions.

The final reaction I ran this week was the second aldol condensation using benzaldehyde. The NMR of the purified product was extremely clean and showed that the product did not need to be purified using flash chromatography. This condensation only had a 52% yield but we believe the benzaldehyde we are using has degraded partially into benzoic acid which could be on reason for a lower yield than expected. This week in lab has set me up to be ready for pushing material towards a natural product next week. These results are helpful in displaying areas that work and those that need improvement in the original procedure but from now one, I will be working forward towards a natural product.

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