Cyclopropoxide

Werstiuk, 1983). Moreover, such a homoenolate anion could eventually undergo ring closure leading to the formation of a cyclopropoxide anion (Chandrasekhar et al., 1981). 

However, reaction with a solution of / -toluenesulfonic acid in refluxing benzene for one hour or with methanolic potassium hydroxide at room temperature for three hours did not produce the expected bicyclic ketones from simple ring cleavage of the cyclopropanol moiety of 1, but instead the tra 5-l,6-dimethylbicyclo[4.3.0]nona-2,7-dione (2) was formed in 60% yield. A cyclopropoxide isomerization was considered to be involved to rationalize this rearrangement. ... 

Cyclopentanone annulation via a cyclopropoxide anion has great synthetic applicability. Construction of the D-ring in estrone can be achieved by base-induced intramolecular cyclization of an appropriately substituted cyclopropanol using sodium hydride as base (Table 2, entry 23-24 jjjg j-esyit is well accounted for by assuming intramolecular carbonyl addition of a j3-acyl carbanion. 

There is an obvious difficulty if the cyclopropane ring is unsymmetrically substituted and our best guideline here is the last stage of the Favorskii reaction,8 e.g. 27 to 31, where a cyclopropoxide ion is protonated 30 at the carbon atom giving the better anion, usually at the less substituted carbon. 

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