Di(hydroperoxy)cycloalkanes Stabilized via Hydrogen Bonding by Phosphine Oxides: Safe and Efficient Baeyer-Villiger Oxidants
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2018 American Chemical Society. The syntheses of two new representatives of di(hydroperoxy)cycloalkane adducts of phosphine oxides, Cy3PO(HOO)2C(CH2)4 and Cy3PO(HOO)2C(CH2)6, and the new hydroperoxy(hydroxy)alkane adduct Cy3PO(HOO)(HO)C(CH2)5 are described. Different synthetic routes were explored. The formation of the adducts proceeds from hydrogen peroxide adducts of phosphine oxides in the presence of cyclic ketones. Additionally, the direct addition of Cy3PO to free di(hydroperoxy)cycloalkanes results in the desired adducts. A mechanism for the formation is proposed, which is supported by generating and identifying the monoperoxy adduct Cy3PO(HOO)(HO)C(CH2)5. All adducts are fully characterized with single-crystal X-ray crystallography, NMR, and IR spectroscopy. All adducts are safe and solid and have shelf lifetimes of months. They are highly soluble in organic solvents, which allows for homogeneous reactions in nonaqueous media. This was demonstrated by selectively oxidizing Ph2P-PPh2 to the moisture-sensitive Ph2P(O)-P(O)Ph2. All adducts Cy3PO(HOO)2C(CH2)4-6 perform efficient Baeyer-Villiger oxidations under mild and anhydrous conditions requiring only catalytic amounts of acid.