| Description |
The Wacker oxidation allows access to methyl ketones from terminal alkenes. This transformation is important for industrial, synthetic, and medicinal chemists, as carbonyls are present in many natural and pharmaceutical products. With the carbonyl, a wide variety of reactions become available, such as the Grignard and the Wittig. Traditional Wacker reaction conditions call for a metal catalyst, typically Pd(II), and an oxidant. These conditions prove challenging for particular substrates such as allylic alcohols and its protected counterparts. The presence of the proximal heteroatom decreases selectivity and can lead to inseparable products. Interested in developing a solution to these challenging substrates, previous members from the Sigman group developed a TBHPmediated Wacker-like oxidation. The proposed key to this method was the quinolineoxazoline (Quinox) ligand. In the reaction, the push-pull nature of the ligand assists Pd in selectively binding the alkene. To further expand the scope of the TBHP-mediated reaction conditions, the system was applied to various internal alkenes with allylic functional groups. For most substrates, the TBHP-mediated conditions selectively produced one product in good yield - a ketone distal from the existing functional group. The method, however, proved to be difficult for cyclic and cis- alkenes generating poor yields. As a whole, the substrate scope for the TBHP-method demonstrated no real need for an electronic bias on internal alkenes and a good tolerance for popularly used protecting groups. |
