An anionic C(3)-C(5) ring expansion of beta-ketocyclopropanes to cyclopentenols.

[reaction: see text] When treated with base, beta-ketocyclopropylcarboxylates ring-open to initially afford either cis or trans alpha,beta-unsaturated ketones. The cis isomer undergoes an intramolecular aldol reaction to afford allylic cyclopentenols in high yield and excellent diastereoselectivity. Choice of base is key to a successful outcome.