Science of Synthesis

Yan, L.; Lin, S.; Liu, P., Science of Synthesis, (2007) 20, 752.

Peroxybenzoic acids are widely used in Baeyer–Villiger reactions. Among them 3-chloroperoxybenzoic acid is the most frequently employed,[‌112‌] whereas 3,5-dinitroperoxybenzoic acid is the most reactive.[‌113‌] The reaction conditions are generally mild so that the β-lactam ketone ‌91‌, which contains a silyl ether group, can be oxidized to the acetate ‌92‌ in quantitative yield (‌Scheme 28‌).[‌114‌] Similarly, the readily enolizable ketone ‌93‌ is readily oxidized by 3-chloroperoxybenzoic acid to the ester ‌94‌ in 90% yield.[‌115‌] For acid-sensitive groups the addition of a base such as sodium hydrogen carbonate is beneficial, as for example in the oxidation of the least sterically hindered 5-acetyl group of the lactone ‌95‌, but here the presence of a radical inhibitor bis(5-tert-butyl-4-hydroxy-2-methylphenyl) sulfide (tbp) is necessary to secure a yield of 50% (‌Scheme 28‌).[‌116‌] Epoxides also survive the reaction conditions and the ketone ‌96‌ affords a 73% yield of the ketone ‌97‌ when it is oxidized by 3-chloroperoxybenzoic acid.[‌117‌] The chiral β-alkoxy ketone ‌98‌ can be stereoselectively converted into the chiral acetal ‌99‌ in 71% yield when 3-chloroperoxybenzoic acid in dichloromethane containing sodium hydrogen carbonate is the oxidant (‌Scheme 28‌).[‌118‌] Baeyer–Villiger reactions using 3-chloroperoxybenzoic acid usually require long reaction times but the addition of trifluoroacetic acid significantly accelerates the oxidation rate.[‌119‌] In a more difficult case, the hindered methyl ketone ‌100‌ affords the acetate ‌101‌ using 3,5-dinitroperoxybenzoic acid in the presence of bis(5-tert-butyl-4-hydroxy-2-methylphenyl) sulfide as the oxidant and radical scavenger, respectively (‌Scheme 28‌).[‌120‌] Monoperoxyphthalic acid converts methyl ketones into acetates, even though attempted oxidations with other peroxybenzoic acids fail.[‌121‌]

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References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8, 888.
• 8.Meeeee-Meee, (8888) 8/8e8, 888.
• 8.Meeeee-Meee, (8888) M 8-8, 888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.