Arene–Alkene Cycloaddition

Abstract

Cycloadditions are among the most efficient chemical processes, combining atom economy, stereospecificity, and the ability to generate molecular complexity in a single step. Aromatic rings would in principle be ideal reaction partners, as they contain, at least from the topological point of view, both olefinic and diene subunits; however, the stability of the conjugated aromatic system would be broken by cycloaddition reactions, which are therefore rarely applied, because kinetics and thermodynamics hinder the process. From that aspect, photochemical activation opens interesting perspectives, as one can selectively provide excess energy to one of the reactants but not to the product, thus preventing thermal back reaction. Indeed, aromatic rings show a rich photochemistry, ranging from isomerizations, substitutions, and additions to cycloadditions. In this review, we will focus on cycloadditions, covering literature from early observations up to the present.

Photochemical Approaches to the Bilobalide Core

“…[13,14] The application of the meta photocycloaddition in the total synthesis of natural products was thoroughly investigated by Wender. [13,14] The application of the meta photocycloaddition in the total synthesis of natural products was thoroughly investigated by Wender.…”

Ge=B π‐Bonding: Synthesis and Reversible [2+2] Cycloaddition of Germaborenes

“…Even heating up to 60 °C in benzene solution does not result in any reconversion of 6 or 7 . Cycloaddition reactions between alkenes and arenes are widely used in organic synthesis because of their high efficiency and selective stereochemistry . In the case of main group element chemistry, some rare examples of [4+2] cycloaddition reactions between unsaturated main group element compounds and arenes have been published.…”

“…Cycloaddition reactions between alkenes and arenes are widely used in organic synthesis because of their high efficiency and selective stereochemistry. [15] In the case of main group element chemistry,s ome rare examples of [4+ +2] cycloaddition reactions between unsaturated main group element compounds and arenes have been published. Recently,S tephan and co-workers reported ar eversible intramolecular [4+ +2] cycloaddition of ap hosphaalkene with an arene ring.…”

Photokatalyse mit sichtbarem Licht: Welche Bedeutung hat sie für die organische Synthese?

“…Sie demonstrierten, dass Anhydride 215 (in situ aus Acylchloriden 214 und Säuren 213 in Ge-genwart von DBU gebildet) in der Metallophotoredox-Katalyse eine Metallinsertion-Decarboxylierung-Rekombination eingehen kçnnen (Schema 62 b). [200] Die Woodward-Hoffmann-Regeln beschreiben die Grundlagen fürd iese Reaktionen, indem sie über HOMO/LUMO-Orbitalsymmetrie und ihre Energielücke den Reaktionsverlauf in Bezug auf Reaktivitätu nd Selektivitätdefinieren. Die abschließende reduktive Eliminierung liefert die gewünschten Ketone 216 in mäßigen bis guten Ausbeuten.…”

“…Cycloadditionen gehçren zu den leistungsfähigsten Methoden, um komplexe Moleküle schnell und stereoselektiv aufzubauen. [200] Die Woodward-Hoffmann-Regeln beschreiben die Grundlagen fürd iese Reaktionen, indem sie über HOMO/LUMO-Orbitalsymmetrie und ihre Energielücke den Reaktionsverlauf in Bezug auf Reaktivitätu nd Selektivitätdefinieren. [201] Die Orbitalsymmetrie bestimmt dabei, ob eine konzertierte Cycloaddition thermisch oder photochemisch ablaufen kann, wobei fürletzteren Reaktionstyp 4n p-Elektronensysteme,i nsbesondere [2+ +2]-Cycloadditionen, von Bedeutung sind.…”