TBN as Organic Redox Cocatalyst for Oxidative Tiffeneau-Demjanov-Type Rearrangement Using O₂ as Sole Oxidant

The Tiffeneau-Demjanov-type rearrangement is a ring-expansion reaction involving the cationic rearrangement of cyclic alcohols. The carbocation intermediates can be generated in situ via various means, including Wacker oxidation. In near recent reports on the reinvestiagtions by Wahl et al. (Sietmann, J.; Tenberge, M.; Wahl, J. M. Wacker Oxidation of Methylenecyclobutanes: Scope and Selectivity in an Unusual Setting. Angew. Chem., Int. Ed. 2023, 62, e202215381) and Zhu et al. (Feng, Q.; Wang, Q.; Zhu, J.-P. Oxidative Rearrangement of 1,1-Disubstituted Alkenes to Ketones. Science 2023, 379, 1363-1368), stoichiometric oxidants were involved. In this work, we report the Tiffeneau-Demjanov-type rearrangement can be smoothly promoted by the Pd-TBN cocatalyzed aerobic Wacker oxidation using molecular oxygen as the sole oxidant. tert-Butanol is essential for achieving high yields. Since the first report by Grigg et al. in 1977 (Boontanonda, P.; Grigg, R. J. Palladium (II)-Catalysed Ring Expansion of Methylenecyclobutanes and Related Systems. J. Chem. Soc. Chem. Commun. 1977, 17, 583-584), the five-decade journey of Pd-catalyzed Tiffeneau-Demjanov-type rearrangement returns to the aerobic again.