Superelectrophilic Aluminum(III)-Ion Pairs Promote a Distinct Reaction Path for Carbonyl-Olefin Metathesis of Medium-Sized Rings

Abstract

We describe the development of a new catalyst system for carbonyl-olefin ring-closing metathesis reactions that relies on Lewis acidic superelectrophiles and significantly expands the current scope of this transformation to medium-sized rings. <div>Importantly, these superelectrophiles are shown to promote carbonyl-olefin metathesis via a distinct and unprecedented mechanism. </div>

Investigation of Lewis Acid-Carbonyl Solution Interactions via Infrared-Monitored Titration

“…With 4 as the titrant, we observe formation of a vibration at 1629 cm −1 as well as trace amounts of unbound 4 between 0 and 2 equiv 4 added (Figure 9B). Beyond 2 equiv 4 added, we still observe the signal at 1629 and 15 (A), 2 and 16 (B), 3 and 17 (C), 37 as well as 4 and 18 (D). 19 Figure 7.…”

“…We recently reported byproduct inhibition for Fe­(III)-catalyzed carbonyl-olefin metathesis that results from this solution behavior . Similarly, Schindler and co-workers used their observations of the solution behavior of FeCl 3 to design a new catalyst system . We are currently using the information yielded from these observations to develop alternative protocols for substrates recalcitrant to current carbonyl-olefin metathesis methods.…”

“…16 Similarly, Schindler and co-workers used their observations of the solution behavior of FeCl 3 12e to design a new catalyst system. 37 We are currently using the information yielded from these observations to develop alternative protocols for substrates recalcitrant to current carbonyl-olefin metathesis methods. Because of the generality of these observations across the examined Lewis acids, we are exploring the impact of highly ligated metal centers on other carbonyl-based, Lewis acid-catalyzed reactions.…”

“…We also observe a series of 1:1 coordination complexes with high affinity interactions. GaCl 3 (15)(16)(17)(18), FeCl 3 (31)(32)(33)(34), and AlCl 3 (35)(36)(37)(38) all form tightly bound complexes with no observable unbound carbonyl present from 0 to 1 equiv added carbonyl. However, the addition of superstoichiometric carbonyl relative to the Lewis acid yields disparate behavior.…”

Exploring the Limits of π‐Acid Catalysis Using Strongly Electrophilic Main Group Metal Complexes: The Case of Zinc and Aluminium

“…Schindler and co-workersr ecently reported ap reprint describ-ing an aluminum-based heterobimetallic ion pair as catalystt o promotecarbonyl-olefin ring-closing metathesis. [27] While the carbonyl-olefinm etathesis discussed above is not relatedt op-acid catalysis, it leads to alkenes that can be activated by p-acids. The tandem carbonyl-olefin/transfer hydrogenation of 17 was thus attemptedw ith 1,4-cyclohexadiene (1,4-CHD) as hydrogen donor (Table7).…”