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29.17.3.1.1.3 Variation 3: Synthesis from Strained Ketones

DOI: 10.1055/sos-SD-129-00159

Coote, S. C.; Smith, L. H. S.; Procter, D. J.Science of Synthesis Knowledge Updates, (20103464.

Cyclopropanones are highly strained ketones which react readily with nucleophiles and also undergo hydration readily. The high reactivity of the cyclopropanone carbonyl group is generally attributed to the relaxation of the ring strain upon conversion of the sp2-hybridized carbonyl carbon atom into sp3-hybridization. Cyclopropanone (prepared as an ethereal solution from ketene and diazomethane) may be hydrated by reaction with moist air to generate the corresponding crystalline hydrate 144 in “excellent yield” (Scheme 52).[‌183‌] After a few days, pure hydrate 144 starts to convert into propanoic acid; this process is hastened by heating the hydrate or upon exposure to alkali. 2-(Trimethylsilyl)cyclopropanone (145), which is reported to be much more stable than cyclopropanone itself, presumably due to steric effects, forms a stable hydrate 146 in 99% yield upon heating in water at 40°C.[‌184‌] In addition, 2,3-di-tert-butylcyclopropanone (147) is hydrated by reaction with water to generate hydrate 148 in 87% yield.[‌185‌] The hydrate is reported to decompose in air and is sensitive to acids and bases. Hydration is reversible, as demonstrated by formation of the corresponding hemiacetal upon addition of methanol to a solution of the pure hydrate.

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