Abstract
An iridium catalyzed method for the synthesis of functionalized cyclohexanes from methyl ketones and 1,5-diols is described. This process operates by two sequential hydrogen borrowing reactions, providing direct access to multisubstituted cyclic products with high levels of stereocontrol. This methodology represents a novel (5 + 1) strategy for the stereoselective construction of the cyclohexane core.
Highlights
We wondered whether a related approach could be used to construct substituted cyclohexane rings by double alkylation of Ph* ketones with 1,5-diols (Scheme 1C).[9] This approach would form two new C−C bonds in a direct manner, enabling the synthesis of a diverse range of cyclohexane products due to the widespread availability of functionalized 1,5-diols
Previous Work and Strategy for Stereoselective Synthesis of Cyclohexanes via Hydrogen Borrowing Catalysis of these strategies rely on the availability of appropriately substituted precursors, and as a result new methods targeting multisubstituted cyclohexanes are of great interest
We have recently reported that pentamethylphenyl (Ph*) ketones can be alkylated with alcohols via hydrogen borrowing catalysis (Scheme 1B).[7]
Summary
We wondered whether a related approach could be used to construct substituted cyclohexane rings by double alkylation of Ph* ketones with 1,5-diols (Scheme 1C).[9] This approach would form two new C−C bonds in a direct manner, enabling the synthesis of a diverse range of cyclohexane products due to the widespread availability of functionalized 1,5-diols. In the presence of catalytic [IrCp*Cl2]2 and KOH in toluene at 105 °C, we were pleased to isolate the desired cyclohexane product 3a in 44% yield (Table 1, entry 1).
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