Strukturen der intermediären Komplexe bei der Friedel‐Crafts‐Acylierung

Abstract

Additionsverbindungen aus Lewis-Sauren MX, und Saurehalogeniden R-COX treten intermediar bei der Friedel-Crafts-Acylierung auf. IR-und NMR-Untersuchungen dieser Zwischenprodukte haben die Existenz von Strukturisomeren wahrscheinlich gemacht. Bei der Rontgen-Strukturanalyse lassen sich zwei Formen unterscheiden: die Molekiilform, in der die Verbindungen als Donor-Acceptor-Komplexe R-CXO-t MX, vorliegen, und die Ionenform, in der sie als Oxocarbenium-Salze [R-CO]+[MX,+ I] ~ formuliert werden konnen. Die Verbindungen vom Donor-Acceptor-Typ R-CXO-tMX, zeichnen sich durch die Bildung einer koordinativen Sauerstoff-Metall-Bindung aus; der Elek tronenubergang vom Sauerstoff zum Metall des Acceptors riihrt immer von einer schwachen Donor-AcceptorWechselwirkung her. Die positive Ladung der Aryloxocarbenium-Ionen ist teilweise uber den aromatischen Kern delokalisiert. Im Gegensatz dazu befindet sich die positive Ladung bei den Alkyloxocarbenium-Ionen im wesentlichen auf dem Kohlenstoffatom der Carbonylgruppe, wie Berechnungen der Elektronendichteverteilung bestatigten.

Lewis Acid Catalyzed Reaction of Arylvinylidenecyclopropanes with Ethyl (Arylimino)acetates: A Facile Synthetic Protocol for Pyrrolidine and 1,2,3,4-Tetrahydroquinoline Derivatives

“…Intermediate C-1 , derived from B-1 via a cyclopropyl ring-opening process, undergoes cyclization to give the corresponding [3 + 2] cycloaddition product 3 when R 7 is an electron-poor aromatic group. However, when R 7 is an electron-rich aromatic group, intramolecular Friedel−Crafts reaction takes place from intermediate B-2 to give intermediate C-2 , which finally furnishes product 4 1 Proposed Mechanism for the Formation of 3 and 4 …”

Lewis-Acid-Catalyzed Rearrangement of Arylvinylidenecyclopropanes: Significant Influence of Substituents and Electronic Nature of Aryl Groups

“…A rational explanation of this drastic difference can be attributed to the nature of Friedel−Crafts reaction . For arylvinylidenecyclopropanes 1k − o having no electron-deficient aromatic substituents, the corresponding 6a H -benzo[ c ]fluorine derivatives 3 were formed with a syn-configuration via a double intramolecular Friedel−Crafts reaction as described in the previous communication 7b…”

“…Therefore, intramolecular Friedel−Crafts reaction takes place from zwitterionic intermediate C ‘- 1 with the aromatic R 3 group at the C-1 position to give the corresponding indene derivative 4 (Scheme ). When R 3 is an electron-neutral or electron-rich aromatic moiety and R 1 and/or R 2 are electron-deficient aromatic moieties/moiety, the subsequent intramolecular Friedel−Crafts reaction cannot easily take place from zwitterionic intermediate C - 1 to provide the corresponding zwitterionic intermediates D - 1 and D ‘ ‘ -1 because intramolecular Friedel−Crafts reaction takes place more easily for electron-rich aromatic moiety, although the corresponding zwitterionic intermediate C - 1 is more stabilized by the electron-rich aromatic moiety of R 3 group. This is why in the case of arylvinylidenecyclopropanes 1p − v having electron-deficient aromatic moieties (R 1 and R 2 or R 3 ), the corresponding indene derivatives 4 are exclusively formed.…”

Facile Synthesis of Tetrahydrofurans from Cycloadditions of Vinylidenecyclopropanes with Aldehydes and Further Tunable Transformations for the Construction of Furan, Indene, and Benzo[c]fluorene Derivatives

“…Second, the ring-opening reaction of oxonium intermediate D produces δ-allylic cationic intermediate E or the reversible cationic intermediate E 1 , E 2 , and E 3 . When R 1 is an electron-rich aromatic moiety or an electron-neutral aromatic moiety (phenyl) and R 2 is an electron-dificient aromatic moiety or alkyl group (methyl), the intramolecular Friedel−Crafts reaction with the aromatic R 1 group exclusively takes place to produce the intermediate F , probably due to the nature of Friedel−Crafts reaction (Table , entries 3 and 4) . The subsequent transformation of F leads to the formation of intermediate G in the presence of Lewis acid.…”