Donor–acceptor cyclopropanes were reacted with amphiphilic benzodithioloimine to give seven-membered heterocycles with two sulfur atoms. Formally, this transformation can be regarded as a [4+3] cycloaddition reaction of the three-membered ring and ortho-bisthioquinone. The benzodithioloimine serves as a surrogate for this highly reactive diene. The structure of the products was confirmed by X-ray crystallography. Broad signals in ¹³C NMR studies suggest that several conformers, slowly interconverting on the NMR timescale, are present at room temperature.

Enynes substituted with a tertiary hydroxyl group attached to one of the alkyne units react with iodobenzenes in a Pd-catalyzed domino reaction. The cascade consists of an intermolecular anti-carbopalladation and a terminating Heck reaction. This process leads to arene-substituted dienes. One tetrasubstituted double bond is embedded in a six-membered ring system, and the other trisubstituted alkene is located in an exocyclic position. On treatment with acid, the emerging tertiary carbocation is attacked by the arene to give a five-membered ring, and thus results in the formation of alkylated indenes.

A novel type of π-helicenes is reported, in which the π-system is truncated to an all-s-cis all-Z oligoene chain. A domino sequence was developed, consisting of up to four consecutive carbopalladation reactions and a terminal Stille cross-coupling, to generate these entities in one step from the respective linear oligoynes. Despite the minimal π-system, very high optical rotation values were encountered for the single enantiomers. X-ray crystallography confirmed their screw-shaped structure.

Formal anti-carbopalladation reactions of CC triple bonds are uncommon, but highly useful transformations. Alkynes can be designed to give anti-carbopalladation products. Prerequisite is the exclusion of other reaction pathways to provoke the cis–trans isomerization of the syn-carbopalladation intermediate. Detailed mechanistic studies of this crucial step by experimental and computational means were performed. Application of an intramolecular version for the synthesis of oligocyclic compounds and substituted dibenzofurans is also described.

A domino approach consisting of up to five consecutive steps to access either highly substituted dispiranes or π-helicenes from oligoyne chains is reported. The domino sequence consists of several carbopalladation reactions, a Stille cross-coupling to obtain the helicenes, and, depending on the steric demands of the helicene, a final 6π-electrocyclization to afford the dispiranes. Formally, the latter transformation contravenes the Woodward–Hoffmann rules, as revealed by X-ray crystallography of the dispirane. Additionally, the racemization barrier of the (Z,Z,Z)-triene-based helicene has been determined by a kinetic analysis and compared with results from density functional theory calculations. Characteristic points on the reaction coordinate were further analyzed according to their relaxed force constants (compliance constants).

An intramolecular domino process consisting of a formal anti-carbopalladation followed by Heck reaction is realized. Complex oligo(hetero)cyclic scaffolds are efficiently obtained in one synthetic step from easily obtainable enyne precursors. In contrast to common syn-carbopalladation reactions of alkyne units, the carbopalladation employed here is designed to afford an anti-arrangement of the two new substituents across the emerging double bond. A prerequisite is that the residues next to the alkyne should lack any β-hydrogen atoms. The method paves the way to tri- and tetrasubstituted double-bond systems that have not been accessible by conventional Pd catalysis.

Formale anti-Carbopalladierungsreaktionen von C-C-Dreifachbindungen sind ungewöhnliche, aber äußerst nützliche Transformationen. Alkine, die gezielt anti-Carbopalladierungsprodukte ergeben, werden vorgestellt. Voraussetzung ist der Ausschluss anderer Reaktionswege, um eine cis-trans-Isomerisierung der entstehenden Doppelbindung zu ermöglichen. Der entscheidende mechanistische Schritt wurde sowohl experimentell als auch theoretisch untersucht. Eine intramolekulare Version der Reaktion ermöglicht die einfache Herstellung sowohl von oligocyclischen Produkten als auch von Dibenzofuranen.

Ein neuartiger Typ von π-Helicenen, deren π-System auf eine all-s-cis-Z,Z,…-Oligoenkette reduziert ist, wird vorgestellt. Eine Dominosequenz aus bis zu vier aufeinanderfolgenden Carbopalladierungen und einer abschließenden Stille-Kreuzkupplung wurde entwickelt, um den einstufigen Aufbau dieser Einheiten ausgehend von den jeweiligen linearen Oligoinen zu ermöglichen. Trotz des minimalen π-Systems wurden für die einzelnen Enantiomere sehr hohe Werte ihrer optischen Rotation festgestellt. Die schraubenförmigen Strukturen wurden durch Röntgenstrukturanalyse zweifelsfrei nachgewiesen.

Ringspannung gewinnbringend zu nutzen, ist seit jeher für den Aufbau komplexer Systeme von großem Vorteil. Schnell richtet sich somit der Blick auf Cyclopropane als Bausteine für die organische Synthese. Auch wenn die Thermodynamik dabei auf der Seite des Synthesechemikers steht, ermöglicht erst ein spezielles Substitutionsmuster am Cyclopropan besonders milde, effiziente und selektive Umsetzungen. Die erforderliche Absenkung der Aktivierungsbarriere wird durch die Kombination von zueinander vicinal stehendem Elektronendonor und -akzeptor erreicht. Dieser Aufsatz beleuchtet die richtigen Hilfsmittel, um mit Donor-Akzeptor-substituierten Cyclopropanen Ringöffnungen, Cycloadditionen und Umlagerungen durchzuführen.

The effective use of ring strain has been applied to considerable advantage for the construction of complex systems. The focus here is directed towards cyclopropanes as building blocks for organic synthesis. Although thermodynamics should take the side of synthetic chemists, only a specific substitution pattern at the cyclopropane ring allows for particularly mild, efficient, and selective transformations. The required decrease in the activation barrier is achieved by the combined effects of vicinal electron-donating and electron-accepting moieties. This Review highlights the appropriate tools for successfully employing donor–acceptor cyclopropanes in ring-opening reactions, cycloadditions, and rearrangements.