Fe2O3eSO3H made the isolation and reuse of this catalyst very
easy. After completion of the reaction, the mixture was triturated
with ethyl acetate. Within a few seconds after stirring was
stopped, the reaction mixture turned clear and catalyst was deposited
on the magnetic bar, which was easily removed using an
external magnet. After being washed with acetone and dried in air,
the nano-g-Fe2O3eSO3H can be directly reused without any deactivation
even after five rounds of synthesis of product 4a
(Table 5).