Understanding the control of the selectivity in oxygenation reactions

Abstract

The synthesis of high valuable oxygenated compounds from crude and cheap raw chemicals is one of the most important transformations in current chemistry. In this context it is highly desirable to enable the use of oxygen as a primary oxidant because oxygen is inexpensive, abundant and environmentally benign. However, oxygenation of olefins with late transition metals produces 3-metalla-1,2-dioxolanes, whose evolution towards oxygenated products is not selective. The two sole exceptions to this behavior are a dianionic iridium complex leading to a 2-iridaoxetane, and a rhodium triazenide complex, both able to incorporate oxygen and transfer it to an olefin with an atomic economy of 100%. In a completely different approach, Wacker type reactions are also a good alternative for the synthesis of high valuable chemicals, in which water and oxygen or hydrogen peroxide are the single subproducts. However most of the Wacker type reported oxidations involve the nucleophilic attack on a coordinated Pd(II) olefin, and only a few related examples with Rh(I) and Ir(I) complexes have been reported. In this communication we will show an iridium complex that promotes both type of olefin functionalization, i.e., the selective insertion of oxygen into olefinic bonds and the nucleophilic attack of a variety of nucleophiles such as alkoxides under controlled conditions. Some illustrative intermediates that show both reactions as the one depicted in the figure will be described.