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

Abstract

Carbonyl-olefin metathesis represents a powerful yet underdeveloped method for the formation of carbon-carbon bonds. So far, no Brønsted acid based method for the catalytic carbonyl-olefin metathesis has been described. Herein, a cocatalytic system based on a simple Brønsted acid (HCl) and a self-assembled supramolecular host is presented. The developed system compares well with the current benchmark catalyst for carbonyl-olefin metathesis in terms of substrate scope and yield of isolated product. Control experiments provide strong evidence that the reaction proceeds inside the cavity of the supramolecular host. A mechanistic probe indicates that a stepwise reaction mechanism is likely.

The Hexameric Resorcinarene Capsule at Work: Supramolecular Catalysis in Confined Spaces

“…In as imilarw ay,T iefenbacher and Catti showed that hexameric CR 6 and cocatalyst HCl worked in as ynergistic wayt o catalyzec arbonyl-olefin metathesis reactions. [18] An example of the capsulee ffect on the chemo-andr egioselectivity of an organic reaction has been reported by Reek et al (Scheme 3). [19] The authors studied the hydration of 11 (66 mm)i nt he presence of CR 6 as an anoreactor (33 mm with respectt o1)a nd 10 (3.3 mm)a sacatalyst (Scheme 3) in water-saturated C 6 D 6 at 70 8C.…”

A Zn4L6 Capsule with Enhanced Catalytic C−C Bond Formation Activity upon C60 Binding

“…Fujita and co‐workers reported an early example of a Pd‐based octahedral cage catalyzing the Diels–Alder reaction . Recently Tiefenbacher and Catti published a study of catalytic carbonyl–olefin metathesis through the combined action of HCl and a self‐assembled supramolecular host . Organometallic catalysts can also be introduced into assemblies to facilitate catalytic reactions by bringing together the catalyst and the substrate .…”

“…Artificial supramolecular catalysts are particularly well adapted to regulation, and have proven useful in a wide variety of synthetic contexts . Many metal–organic cages have been developed as supramolecular catalysts, where a substrate enters, is transformed, and exits again. Fujita and co‐workers reported an early example of a Pd‐based octahedral cage catalyzing the Diels–Alder reaction .…”

Catalytic Carbonyl-Olefin Metathesis of Aliphatic Ketones: Iron(III) HomoDimers as Lewis Acidic Superelectrophiles

“…[4][5][6] Upon binding to a Lewis acid catalyst, such as FeCl3, the carbonyl functionality is activated to perform a [2+2]-cycloaddition forming an intermediate oxetane, which subsequently undergoes a retro-[2+2]-cycloaddition resulting in the desired metathesis product. While successful protocols for intramolecular and intermolecular Lewis acid-catalyzed carbonyl-olefin metathesis have been reported following this reaction design principle, 7,8 all current procedures rely exclusively on aryl carbonyls as substrates while the reaction of aliphatic ketones remain elusive. [4][5][6][7][8] We report herein the development of a catalytic carbonyl-olefin ring-closing metathesis of aliphatic ketones that proceeds in yields up to 94% and tolerates a variety of functional groups.…”

“…While successful protocols for intramolecular and intermolecular Lewis acid-catalyzed carbonyl-olefin metathesis have been reported following this reaction design principle, 7,8 all current procedures rely exclusively on aryl carbonyls as substrates while the reaction of aliphatic ketones remain elusive. [4][5][6][7][8] We report herein the development of a catalytic carbonyl-olefin ring-closing metathesis of aliphatic ketones that proceeds in yields up to 94% and tolerates a variety of functional groups. Mechanistic investigations reveal a distinct mode of activation for aliphatic ketones relative to their aromatic analogs in which the formation of a homobimetallic singly-bridged iron(III)-dimer as the active catalytic species enables the formation of a significantly enhanced electrophilic moiety.…”