Highly Active Nickel Catalysts for the Isomerization of Unactivated Vinyl Cyclopropanes to Cyclopentenes

Transition Metal-Catalyzed Reactions Using N-Heterocyclic Carbene Ligands (Besides Pd- and Ru-Catalyzed Reactions)

“…In combination with a phosphine ligand, activated VCPs could be converted to the corres-ponding cyclopentenes at elevated temperatures. Recently, it was shown that replacement of the phosphine ligand with an NHC ligand led to a dramatic increase in catalytic activity [3]. Sterically hindered N-aryl-substituted NHCs, such as IPr or SIPr, gave greater yields of isomerized products at faster reaction rates than less bulky NHCs (such as ICy and IiPrim).…”

“…phosphines such as P(Cy) 3 . The ration of allylic and homoallylic products was excellent (> 95 : 5) but significant erosion of enantiomeric purity (95 to 62%) occurred.…”

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

“…[52] Eine Nickel(0)-katalysierte Vinylcyclopropan-Cyclopenten-Umlagerung verläuft in Gegenwart N-heterocyclischer Carbene (NHCs) bei Raumtemperatur (Tabelle 7, Eintrag 4). [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).…”

A reductive coupling strategy towards ripostatin A

“…First, substrates containing a vinyl cyclopropane unit had not been previously tested under nickel-catalyzed reductive coupling conditions. Nickel(0) is known to catalyze the rearrangement of vinylcyclopropanes to cyclopentenes; however, activating substituents are commonly required [19–21]. Furthermore, application of a proposed 1,5-hydrogen rearrangement to ripostatin A would require that the reaction proceed to give the triene with E,E,E configuration selectively out of four possible configurational outcomes (Scheme 2).…”