Zinc-Catalyzed β-Functionalization of Cyclopropanols via Enolized Homoenolate

We report herein a zinc-catalyzed beta-allylation of cyclopropanols with Morita-Baylis-Hillman (MBH) carbonates with retention of the cyclopropane ring. The reaction is promoted by a zinc aminoalkoxide catalyst, affording cyclopropyl-fused alpha-alkylidene-delta-valerolactone derivatives in moderate to good yields. Mechanistic experiments suggest that the present reaction does not proceed via direct beta-C-H cleavage of the cyclopropanol, but involves zinc homoenolate and its enolization to generate a key bisnucleophilic species. alpha-Allylation of this enolized homoenolate with MBH carbonate would be followed by regeneration of the cyclopropane ring and irreversible lactonization. The enolized homoenolate mechanism has also been proven to allow for beta-functionalization with alkylidenemalononitrile as the reaction partner. A sequence of the present reaction and known cyclopropanol transformation provides an opportunity to transform a simple cyclopropanol into alpha,beta- or beta,beta-difunctionalized ketones.

Automated summary

A zinc-catalyzed beta-allylation of cyclopropanols with Morita-Baylis-Hillman (MBH) carbonates was reported, maintaining the cyclopropane ring and yielding cyclopropyl-fused alpha-alkylidene-delta-valerolactone derivatives. The mechanism involves zinc homoenolate formation and enolization, followed by alpha-allylation with MBH carbonate leading to cyclopropane ring regeneration and irreversible lactonization, allowing for beta-functionalization with alkylidenemalononitrile as well. This reaction provides a pathway to transform simple cyclopropanols into alpha,beta- or beta,beta-difunctionalized ketones.