Abstract
Over the last few decades, the quest for environmentally benign chemical transformations has become an important topic in both industrial and academic research. We developed several highly atom-economical direct reactions, such as direct conversion of esters to oxazolines and transesterification, catalyzed by μ4-oxo-tetranuclear zinc cluster Zn4(OCOCF3)6O (1b). Because the reaction conditions are almost neutral, various acid-sensitive functionalities (THP ether, TES ether, Boc carbamate, and so on) persisted and no epimerization of α-position of ester occurred. The most attractive highlight of the zinc cluster catalysis is that hydroxyl groups are selectively acylated in the presence of primary and secondary aliphatic amino groups. Such advantageous catalytic performance is due to assembled metal ions that serve as a functional model of metalloenzyme containing more than two metal ions, but different from mononuclear catalysts and other previously reported catalysts.
