Nickel‐Catalyzed Cyclopropanation with NMe₄OTf and nBuLi

Abstract

Nickel was identified as a catalyst for the cyclopropanation of unactivated olefins by using in situ generated lithiomethyl trimethylammonium triflate as a methylene donor. A mechanistic hypothesis is proposed in which the generation of a reactive nickel carbene explains several interesting observations. Additionally, our findings shed light on a report by Franzen and Wittig published in 1960 that had been retracted later owing to irreproducibility, and provide a rational basis for the systematic development of the reaction for preparative purposes as an alternative to diazomethane or Simmons-Smith conditions.

Reductive Cyclopropanations Catalyzed by Dinuclear Nickel Complexes

“…[1] Despite the collective synthetic utility of these reactions,apersistent limitation is the scope of carbene precursors.D iazoalkane reagents are inherently unstable in the absence of electron-withdrawing substituents.C onsequently,d iazoacetates,a nd their derivatives,a re the most common class of substrates in reported methods.G iven the abundance of natural products,p harmaceutical compounds,a nd fine chemicals containing cyclopropanes with one or more unsubstituted carbon atoms, ageneral catalytic approach for the transfer of the parent CH 2 group would be of significant value. [3] In principle,t he use of diazomethane in carbene transfer reactions [4] could be circumvented by accessing reactive methylene equivalents reductively from dihalomethanes. Indeed, the Simmons-Smith cyclopropanation, which was first reported in 1958, operates in this way and continues to represent the most viable method for CH 2 transfer (Figure 1b).…”

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

“…The possible reaction mechanisms leading to cyclopropanes and the kinetically unusual formation of ethylene were examined on a model system by means of DFT calculations (Figure ). Initially, a purely dissociative mechanism analogous to the proposed formation of carbenes from carbenoids of Pd and Ni was considered. Complete dissociation of the triflate anion from the activated carbenoid 12 leads to the formation of a gold methylidene 13 from which cyclopropanation of norbornene can occur without an apparent barrier (Supporting Information, Figure S31).…”

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

“…[27] Thep ossible reaction mechanisms leading to cyclopropanes and the kinetically unusual formation of ethylene were examined on am odel system by means of DFT calculations (Figure 3). Initially,apurely dissociative mechanism analogous to the proposed formation of carbenes from carbenoids of Pd [28] and Ni [29] was considered. Complete dissociation of the triflate anion from the activated carbenoid 12 leads to the formation of ag old methylidene 13 from which cyclopropanation of norbornene can occur without an apparent barrier (Supporting Information, Figure S31).…”