Catalytic Conversion of Furans and Pyrroles to Natural Products and Analogues Utilizing Donor‐Acceptor Substituted Cyclopropanes as Key Intermediates

Abstract

This review is an account of our work on developing stereoselective cyclopropanations of furans and pyrroles as a facile entry into donor‐acceptor substituted cyclopropanes. The application of these building blocks for the synthesis of paraconic acids, sesquiterpene lactones, pyrrolidinones, and conformationally restricted β‐amino acids is discussed.

Inherent Reactivity of Spiro‐Activated Electrophilic Cyclopropanes

“…[4,5] The polarization of the C1À C2 bond in the DACPs not only favorably enhances reactivity toward nucleophiles but also steers regioselectivity of nucleophilic attack toward the already substituted C2 position. [1] Nowadays eCPs are regularly employed as precursors for carbo- [6] and heterocycles, [7,8] and asymmetric cyclopropanations have made DACPs useful tools for the synthetic chemist. [9,10] Ring opening, [5e] (3 + 2), (3 + 3), and (4 + 3) cycloadditions [11] as well as rearrangements [12] of functionalized cyclopropanes offer access to a multitude of building blocks.…”

Stereoselective Synthesis of Tropanes via a 6π‐Electrocyclic Ring‐Opening/ Huisgen [3+2]‐Cycloaddition Cascade of Monocyclopropanated Heterocycles

“…Monocyclopropanated heteroarenes 4 and 5 (R 2 =CO 2 R) are readily available in diastereo‐ and enantiopure form by the cyclopropanation of pyrroles and furans with diazoacetates, all representing inexpensive, renewable resources. Such compounds have been proven to be of great synthetic value, being associated with the facile cleavage of the activated, exocyclic , donor‐acceptor substituted cyclopropane bonds . In the context of the synthesis of tropanes, this reactivity was most elegantly exploited by Davies and co‐workers with the cyclopropanation of pyrroles by vinyldiazoacetates followed by a Cope rearrangement (Scheme b) .…”

Stereoselektive Synthese von Tropanen über eine 6π‐elektrocyclische Ringöffnung/ Huisgen‐[3+2]‐Cycloadditionskaskade von monocyclopropanierten Heterocyclen

“…Die monocyclopropanierten Heteroarene 4 und 5 (R 2 =CO 2 R) sind durch die Cyclopropanierung von Pyrrolen und Furanen mit Diazoestern, kostengünstige und erneuerbare Ressourcen, in diastereo‐ und enantiomerenreiner Form leicht zugänglich. Solche Cyclopropane haben sich als vielseitige Synthesebausteine bewährt, da deren aktivierten, exocyclischen Donor‐Akzeptor‐substituierten Cyclopropanbindungen selektiv geöffnet werden können . Im Zusammenhang mit der Synthese von Tropanen wurde diese Reaktivität von Davies und Mitarbeiter durch die Cyclopropanierung von Pyrrolen durch Vinyldiazoester mit anschließender Cope‐Umlagerung erfolgreich genutzt (Schema b) .…”