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26.6.5.1.1.5 Variation 5: By Oxidation with a Molybdenum Complex

DOI: 10.1055/sos-SD-026-00761

Suffert, J.Science of Synthesis, (200526938.

Lithium enolates, formed from ketones having α-methylene or α-methine groups, are oxidized at low temperature with (hexamethylphosphoric triamide)oxodiperoxy(pyridine-N)molybdenum(VI) [213, L1=1-pyridine; L2=OP(NMe2)3; (MoOPH)] to give the corresponding α-hydroxy derivatives 214, after the hydrolysis of intermediate lithium salts (Scheme 99). Suitable ketones include unsymmetrical cyclic ketones and cyclohexenones; however, reactions with the enolates from methyl ketones are not always successful. Hydrolysis of the intermediates is best achieved by the addition of saturated aqueous sodium sulfite and then water. Sodium sulfite apparently reduces unreacted molybdenum(VI) species to water-soluble salts, thereby facilitating the isolation of the α-hydroxy ketones. A simple aqueous workup can also be used, but this typically gives emulsions, a lower material balance, and highly colored molybdenum-containing byproducts, which are soluble in organic solvents. In a typical example the cyclobutanone 215 is oxidized to give the hydroxy ketone 216 in 81% yield (Scheme 99).[‌188‌] This type of hydroxylation process does not afford the products of oxidative CC bond cleavage, although if the initially formed intermediates are heated α-dicarbonyl compounds are formed in low yields.

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