I am having a problem with this product. This chemical is synthezed from buchwald coupling as shown. After reaction, the mixture is purified through a silica column (200-300 mesh silica, PE/EA) and then trituration in hot EtOAc/DCM/PE mixture to afford 17g white powder. On TLC, it is a fluorescence dot under UV light(Rf=0.3, DCM/EA=1:1), which looks very pure. However, on RP-HPLC the purity is about only 90%, while the impurities has higher retention time (less polar). We tried different chromogenic agents such as I2 and phosphomolybdic acid. Still no impurity is observed on TLC.
Thus, we did a second silica column (300-400mesh silica, DCM/EA) and then trituration in hot EtOAc/DCM mixture. However, the purity on HPLC does not change a lot, even the first 3g elute was cut on column.
The only explaination I have is this weird isomerization. But I cannot convince myself and my client about this isomerization.
Do you think this is possible?
Thanks a lot.