Zinc‐Mediated Diastereoselective Annulation of Cyclopropanols with Alkylidenemalononitriles via Enolized Homoenolate

A zinc-mediated annulation of cyclopropanols with alkylidenemalononitriles produces structurally unique cyclopropane-fused 6-amino-3,4-dihydro-2H-pyran-5-carbonitrile derivatives in moderate to good yields with high diastereoselectivity. Featuring an in situ-generated enolized homoenolate as the key intermediate, this reaction tolerates a variety of substituted cyclopropanols and alkylidenemalononitriles.

Abstract

A zinc-mediated annulation reaction between cyclopropanols and alkylidenemalononitriles is reported. The reaction is promoted in the presence of Et₂Zn and 1,4-diazabicyclo[2.2.2]octane (DABCO) in DMSO at 80 °C, affording cyclopropane-fused 6-amino-3,4-dihydro-2H-pyran-5-carbonitrile derivatives in moderate to good yields with high diastereoselectivity. The reaction is proposed to involve an enolized homoenolate as the key reactive intermediate, which is generated through ring opening of zinc cyclopropoxide and enolization of the resulting zinc homoenolate. The enolate moiety of this reactive species undergoes Michael addition to the alkylidenemalononitrile, which is followed by ring closure of the resulting α-functionalized homoenolate and intramolecular cyclization between the cyclopropoxide and one of the cyano groups.

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