Mechanistic Investigations of the Iron(III)-Catalyzed Carbonyl-Olefin Metathesis Reaction

Abstract

Iron(III)-catalyzed carbonyl-olefin ring-closing metathesis represents a new approach toward the assembly of molecules traditionally generated by olefin-olefin metathesis or olefination. Herein, we report detailed synthetic, spectroscopic, kinetic, and computational studies in order to determine the mechanistic features imparted by iron(III), substrate, and temperature to the catalytic cycle. These data are consistent with an iron(III)-mediated asynchronous, concerted [2+2]-cycloaddition to form an intermediate oxetane as the turnover limiting step. Fragmentation of the oxetane via Lewis acid-activation results in the formation of 5- and 6-membered unsaturated carbocycles.

Brønsted Acid‐Catalyzed Carbonyl‐Olefin Metathesis inside a Self‐Assembled Supramolecular Host

“…[6] In accordance with the literature,t he corresponding electron-poor chloroarene 13 proved resistant to the metathesis reaction, and additional HCl was required to achieve areasonable reaction time.T he d,e-unsaturated ketones 15, 17,and 19 were converted cleanly into the corresponding cyclopentenes (entries 8-10). Intrigued by the seemingly contradictory reports on the mechanism of the oxetane formation by the groups of Schindler and Li, [8,9] we decided to investigate the mechanism for the hexamer I/HCl system, by employing the mechanistic probe 29 (Scheme 1a nd Chapter 7i nt he Supporting Information). Unfortunately,p reliminary attempts to catalyze intermolecular carbonyl-olefin metathesis between benzaldehyde and acyclica lkenes remained unsuccessful.…”

“…[5] However,the reaction requires afivefold excess of the carbonyl component and is restricted in terms of substrate scope.F inally,i n2 016, ab reakthrough in carbonyl-olefin metathesis was accomplished by Schindler and co-workers by utilizing catalytic amounts of FeCl 3 . [9] Supramolecular host systems are increasingly investigated for their ability to facilitate reactions that are difficult to perform in bulk solution. [6,7] Shortly thereafter, as imilar approach was described by the Li group for the construction of carbo-and heterocyclica lkenes.…”

Interrupted Carbonyl‐Alkyne Metathesis

“…[1][2][3][4][5] Several Lewis acids have been identified for their ability to catalyze this transformation, including FeCl 3 , [6] GaCl 3 , [7] I 2 , [8] trityl [9] and tropylium [10] tetrafluoroborate salts, resulting in a variety of cyclopentenes, cyclohexenes, polyaromatic hydrocarbons, and functionalized pyrrolines. [11] In comparison, under Brønsted acid catalysis this reaction path was shown to be interrupted to result in the formation of tetrahydrofluorenes 3 ( Figure 1B). [11] In comparison, under Brønsted acid catalysis this reaction path was shown to be interrupted to result in the formation of tetrahydrofluorenes 3 ( Figure 1B).…”

Brønsted‐Säure‐katalysierte Carbonyl‐Olefin‐Metathese in einer selbstorganisierten supramolekularen Wirtstruktur

“…Des Weiteren wurde eine Lewis-Säure-katalysierte intermolekulare Carbonyl-Olefin-Metathese durch FranzØn et al unter Verwendung von 20 Mol-% Tr ityltetrafluoroborat beschrieben. [9] Supramolekulare Wirtsysteme werden vermehrt wegen ihrer Fähigkeit untersucht, in Lçsung schwierig durchführbare Reaktionen zu ermçglichen. [6] Die entwickelte Methode zeichnet sich durch eine relativ große Substratbreite,m ilde Reaktionsbedingungen und eine einfache Durchführbarkeit aus.…”

“…Die Umsetzung von b-Ketoestern mit elektronenreichen Aren-Einheiten(7,9,11)l ieferte die zugehçrigen Cyclopenten-Derivate(8,10,12)i ng uten bis exzellenten Ausbeuten. Die GC-Analyse zeigte vollständigen Umsatz nach 2T agen an.…”