Hemiketals from cyclopropanones

Thus the hemiketal from cyclopropanone will have 109.5° — 60° = 49.5°, and that from cyclobutanone 109.5° — 90° = 19.5° of strain at Cl. This change in the angle strain means that a sizable enhancement of both the reactivity and equilibrium constant for addition is expected. In practice, the strain elfect is so large that cyclopropanone reacts rapidly with methanol to give a stable hemiketal from which the ketone cannot be recovered. Cyclobutanone is less reactive than cyclopropanone but more reactive than cyclohexanone or cyclopentanone. 

An early preparation of these aminocyclopropanols from the hemiketals of cyclopropanone was described by Wasserman and Baird . Another early description of these types of carbinol amines was provided by de Boer and coworkers who used 1-acetoxycyclopro-panol as the cyclopropanone source . ... 

The polymerization of cyclopropanone is initiated °) by traces of water and is inhibited 15> by moisture scavengers such as acetyl chloride. The terminal groups are apparently hemiketal units since a,co-diacetoxy-poly(oxycyclopropylidenes) 85 are isolated from a mixture of cyclopropanone hydrate, diazomethane and excess ketene. 80>... 

Cyclopropanones are usually not isolated as discrete entities since they rapidly undergo polymerization or ring-opening, especially in the presence of acids or bases. For this reason, much of the chemistry of cyclopropanone and its derivatives has been observed through the behavior of transient intermediates such as hemiketals formed in situ from precursors ... 

Ring-opening reactions of cyclopropanone hemiketals are well known. Under appropriate conditions, cleavage of trimethylsilyl protected hemiketals can provide a synthetically useful route to homoenolate anions as noted earlier (Scheme 20). The reaction of an isopropoxy-titanium homoenolate (128) derived from 127 with an aldehyde has recently been used as the key step in the stereocontrolled construction of the steroidal side-chain of depresosterol (Scheme 49) ... 

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