Studies on the BF3·Et2O catalyzed Baeyer–Villiger reaction of spiroketalic steroidal ketones

During reactions of 23-oxosapogenins and the corresponding isomeric 22-oxo-23-spiroketals with MCPBA in the presence of BF3·Et2O, equilibration occurs between the ketones. The Baeyer–Villiger type oxidation is followed by fragmentation to the dinorcholanic lactones and 3-methylbutyrolactone. The mechanistic aspects of these reactions in the 25R and 25S series are discussed.

Figure optionsDownload as PowerPoint slideResearch highlights▶ 16β,23:23,26-Diepoxy-22-ones are unreactive to Baeyer–Villiger reaction with MCPBA. ▶ 23-Oxosapogenins and 16β,23:23,26-diepoxy-cholestan-22-ones undergo fast Baeyer–Villiger reaction with MCPBA under BF3·Et2O catalysis to produce dinorcholanic lactones as the sole product in good to excellent yields. ▶ BF3·Et2O catalyzes the equilibration between 23-oxosapogenins and 16β,23:23,26-diepoxy-cholestan-22-ones. ▶ The 23-oxosapogenin ⇆ 16β,23:23,26-diepoxy-cholestan-22-ones equilibrium is considerably shifted to the later compound.