Mechanism of the Ni(0)-Catalyzed Vinylcyclopropane−Cyclopentene Rearrangement

Abstract

A combination of physical organic experiments and quantum chemical calculations were used to construct a detailed mechanistic model for the Ni(0)-N-heterocyclic carbene-catalyzed vinylcyclopropane-cyclopentene rearrangement that involves a muti-step oxidative addition/ haptotropic shift/reductive elimination pathway. No evidence for the intermediacy of radicals or zwitterions was found. The roles of substituents on the vinylcyclopropane substrate and variations in the ligands on Ni were evaluated. It is postulated that bulky carbene ligands facilitate formation of the active catalyst species.

Transition Metal Intervention for a Classic Reaction: Assessing the Feasibility of Nickel(0)-Promoted [1,3] Sigmatropic Shifts of Bicyclo[3.2.0]hept-2-enes

“…14 In the analogous rearrangement of vinylcyclopropane, oxidative addition leads to a metallacyclobutane intermediate that rearranges to an η 3 -allyl, η 1 -alkyl intermediate with a very low barrier. 5 However, oxidative addition for A 1 (via TS-A 1 ) leads directly to the η 3 -allyl, η 1 -alkyl intermediate B 1 with an energy barrier of approximately 30 kcal/mol ( Figure 2). The 16-electron intermediate B 1 then rearranges to T-shaped metallacycle C 1 via TS-B 1 .…”

“…11 This methodology was used previously to model a variety of transition metalpromoted reactions, 12 including Ni(0)-promoted [1,3] sigmatropic shifts. 5 Transition-state structures and minima were characterized with frequency calculations, and intrinsic reaction coordinates (IRC) 13 were computed to connect the transitionstate structures with associated minima. In some cases, split basis sets (LANL2DZ for Ni, 6-31G(d) for other atoms) were also used; see text for details.…”

“…Although much attention has been paid to the potential of transition metals (with associated ligands) to catalyze and control the regio-and sterochemical outcome of the cycloaddition and electrocyclization flavors of pericyclic reactions, 7 there are comparatively few examples of transition metal-promoted sigmatropic shifts. 5,6,8 …”

Synergistic Catalysis: Asymmetric Synthesis of Cyclopentanes Bearing Four Stereogenic Centers

“…Several research groups reported similar reactions, almost at the same time, showing the popularity and high competition of this field. 6 The proposed mechanism can be shown in Scheme 2: in the presence of palladium complex the vinylcyclopropane 1 is cleaved by oxidative addition of the palladium 7 and the corresponding zwitterionic -allylpalladium intermediate 4 is generated. On the other hand, the enal reacts with the chiral secondary amine I to form the iminium ion intermediate 5.…”

Von der Entdeckung bis zur Anwendung: 50 Jahre Vinylcyclopropan‐Cyclopenten‐Umlagerung und ihre Bedeutung in der Naturstoffsynthese

“…[53] Die Reaktion wurde später mit rechnerischen Methoden eingehend untersucht. [54] Die vor kurzem von Njardarson et al beschriebene Kupferkatalyse ermöglicht mildere Bedingungen bei den Umlagerungen von Vinyloxiranen in Dihydrofurane (Tabelle 7, Eintrag 5), [55] Vinylthiiranen in Dihydrothiophene (Eintrag 6) [56] und Vinylaziridinen in Pyrroline (Eintrag 7). [57] In den vergangenen zehn Jahren sind mehrere Übersichten zur Chemie der Vinylcyclopropane erschienen.…”