Rhodium(II)-Catalyzed Isomerization of Cyclopropenylmethyl Esters into (Acyloxymethylene)cyclopropanes

Recent progress on donor and donor-donor carbenes

Donor and donor-donor carbenes are two important kinds of carbenes, which have experienced tremendous growth in the past two decades. This review provides a comprehensive overview of the recent development of donor and donor-donor carbene chemistry. The development of this chemistry offers efficient protocols to construct a wide variety of C-C and C-X bonds in organic synthesis. This review is organized based on the different types of carbene precursors, including diazo compounds, hydrazones, enynones, cycloheptatrienes and cyclopropenes. The typical transformations, the reaction mechanisms, as well as their subsequent applications in the synthesis of complex natural products and bioactive molecules are discussed. Due to the rapidly increasing interest in this area, we believe that this review will provide a timely and comprehensive discussion of recent progress in donor and donor-donor carbene chemistry.

Recent developments in cyclopropene chemistry

As readily accessible strained carbocycles, cyclopropenes show a diverse range of reactivities, and a lot of novel and useful transformations have been developed.

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

Cyclopropenes constitute useful precursors of other classes of compounds incorporating a three-membered ring. Although the transformation of substituted cyclopropenes into alkylidenecyclopropanes can be accomplished through different strategies, this review is focusing specifically on the use of [2,3]- and [3,3]-sigmatropic rearrangements involving cyclopropenylcarbinol derivatives as substrates. These sigmatropic rearrangements, which have been developed in recent years, allow a remarkably efficient and stereoselective access to a wide variety of heterosubstituted and/or functionalized alkylidenecyclopropanes which would not be readily accessible by other strategies. The different [2,3]- and [3,3]-sigmatropic rearrangements of cyclopropenylcarbinol derivatives disclosed to date, as well as the analysis of their substrate scope and some applications of the products arising from those reactions, are presented in this review.

Ruthenium Catalyzed Rearrangement of Ene-cyclopropenes. Divergent Reaction Pathways

The reaction of ene-cyclopropenes with Cp*RuCl(cod) leads to alkenyl bicyclo[3.1.0]hexanes, bicyclo[4.1.0]heptanes, and bicyclo[5.1.0]octanes. This reaction involves a reverse regioselectivity in the cyclopropene opening than with gold chlorides. With gem-disubstituted cyclopropenes, a novel cycloisomerization based on ring-opening nucleophilic attack and rearrangement is observed. Alternatively, some gem-disubstituted cyclopropenes give dimerizations of the intermediate carbene.

Synthesis of Chiral cis-Cyclopropane Bearing Indole and Chromone as Potential TNFα Inhibitors

Conformationally restricted analogues of SPD-304, the first small-molecule TNFα inhibitor, in which two heteroaryl groups, indole and chromone, are connected by chiral methyl- or ethyl- cis-cyclopropane, were designed. Synthesis of these molecules was achieved via Suzuki-Miyaura or Stille coupling reactions with chiral bromomethylenecyclopropane or iodovinyl- cis-cyclopropane as the substrate, both of which were prepared from chiral methylenecyclopropane as a common intermediate, constructing the heteroaryl-methyl or -ethyl- cis-cyclopropane structures as key steps. This study presents an efficient synthesis of a series of chiral cis-cyclopropane conjugates with two heteroaryl groups.