We prepared the trichloromethylimidate of tetraacetylglucopyranoside (the Schmidt donor) and an alcohol with the intent of forming a glycosidic bond. We followed a protocol that had used BF3-etherate as the Lewis acid promoter and ran the reaction in the presence of 4 angstrom sieves. Dry DCM was the solvent. Following the suggestion of a colleague, we worked on a small scale and tried to isolate the steps of the reaction: quenching, extraction, and purification. We followed the disappearance of the Schmidt donor by TLC. There was a small excess of alcohol to Schmidt donor. We initially stored the reaction at -80 °C, then we quenched with TEA, which was the only deliberate deviation from the protocol that we were following. Those authors used aqueous sodium bicarbonate as the quench (other workers used TEA). The reason that we used TEA was to isolate the quench step from the extraction step; however, if I had this to do over again, I would just go with bicarbonate and not worry about isolating the quench step from the extraction step.
We removed the solvent and dried in vacuo. We took H-1 and P-31 NMR data. The H-1 suggested that the integral in the acetyl methyl region was about 1/3 of the expected value. In the starting material, the hydrogen at C-1 is a doublet near 6.6 ppm. We saw a broad signal in the same area. The NH signal of the Schmidt donor is no longer present. There are two populations of triplets in the general vicinity of where I would expect OCH2CH3 to show up. The P-31 NMR data suggested the presence of three populations of molecules.
In my informal survey of conditions in various papers, I found large variations in temperature, time, and mole ratios of Schmidt donor to alcohol to BF33-etherate. I am not sure about what to try next. I can supply more details if that would be helpful.