Realization of Anti-Markovnikov Selectivity in Pd-Catalyzed Oxidative Acetalization and Wacker-Type Oxidation of Terminal Alkenes.

Abstract

Catalytic oxidative acetalization and Wacker-type oxidation of terminal alkenes normally proceed with Markovnikov selectivity to afford internally oxyfunctionalized compounds, such as internal acetals and ketones. Thus, the realization of anti-Markovnikov (AM) selectivity in these reactions is challenging. This account focuses on our recent development of Pd-catalyzed AM oxidation of terminal alkenes (mainly styrenes and aliphatic alkenes), that is, oxidative acetalization (oxidation to terminal acetals) and Wacker-type oxidation (oxidation to aldehydes). The key factors that enhance the yield and AM selectivity of the products found in our studies are: 1) the steric bulkiness of the oxygen nucleophiles that attack on the coordinated alkenes, 2) the electron-deficient cyclic alkenes as additives that withdraw electrons from Pd, 3) the slow addition of substrates in the case of the aliphatic alkenes, which suppresses the isomerization of the terminal alkenes into internal alkenes, and 4) the halogen directing groups in the case of aliphatic alkenes.