This is an update on my second attempt at the reduction of a Weinreb amide. This reaction was let run for about 24 hours at 0-5 °C, then for about the same amount of time at room temperature. My reason for doing so was that I wanted to see the starting material disappear entirely, but that never happened. Either there was some unreacted starting material, or there was a side-product that had a similar Rf value. The last several TLC plates, which were run over these two days, looked similar. There was a less intense spot with a higher Rf than the starting material, a more-intense spot with about the same Rf as starting material, and a faint spot with a lower Rf than starting material. I worked the reaction up with KHSO4 and purified over silica (50:1 w/w) using 60:40 hexanes/ethyl acetate. I was able to isolate two products, but I did not see a product corresponding to the slowest-moving spot by TLC. One fraction was a mixed product by TLC, and I did not combine this with either pool.
I have analyzed the 1H NMR of the two chromatographic pools in a preliminary way Pool 1 has a main product that has a characteristic aldehyde proton. However, there appears to be a second product in which there are two singlets that might correspond to the fragment -N(CH3OCH3. The chemical shift of one of these is close to the predicted shift for the Weinreb amine that would be produced upon over-reduction. Based on the integration, here is 70-85% presumed aldehyde, and 15-30% presumed Weinreb amine. Pool 2 has two singlets at the same chemical shift of the two methyl groups as the starting material.