Reagents for the α-Acyloxylation of Aldehydes and Ketones

α-Acyloxylated carbonyl compounds are important in organic synthesis, since they are present in many natural products, pharmaceuticals and synthetic intermediates. The three hydroxylamine hydrochlorides described above provide a practical method for the α-acyloxylation of carbonyl compounds. 1 is an effective reagent for the α-benzoyloxylation of both aldehydes and ketones.^1,2)　An analog with a bulky N-tert-butyl group 2 allows the chemoselective α-benzoyloxylation of aldehydes, since it is completely inert to ketones.^1,2) 3 is a reagent for the introduction of the acetyloxy group in aldehydes.³⁾

Typical Procedure: ^1,2)
1,4-Cyclohexanedione mono-ethylene ketal (4.68 g) and 1 (5.63 g) are dissolved in DMSO (7.5 mL) and the resultant mixture is stirred at room temperature for 1 h. The solution is subsequently diluted with ethyl acetate (300 mL) and washed repeatedly with saturated aqueous brine to remove the reaction solvent (5 x 250 mL). The organic fraction is dried over magnesium sulfate and concentrated in vacuo to give a brown solid as a crude product. The crude solid is recrystallized from isopropyl alcohol (5 mL). The resultant solid is washed with ice-cold isopropyl alcohol (50 mL) and ice-cold petroleum ether (50 mL) before being dried under high vacuum (0.07 kPa) for 8 h to yield the 2-benzoyloxylated compound as pale yellow needles (6.38 g, Y. 77%).