An Efficient, Facile, and General Stereoselective Synthesis of Heterosubstituted Alkylidenecyclopropanes

Copper(I)-Catalyzed Asymmetric Hydrophosphination of 3,3-Disubstituted Cyclopropenes

Herein, a copper(I)-catalyzed asymmetric hydrophosphination of 3,3-disubstituted cyclopropenes is reported. It provides a series of phosphine derivatives in high to excellent diastereo- and enantioselectivities. The methodology enjoys broad substrate scope on both 3,3-disubstituted cyclopropenes and diarylphosphines. The high stereoselectivity is attributed to both the high stability of the Cu(I)-(R,R)-QUINOXP* complex in the presence of stoichiometric HPPh2 and the produced phosphines, and the high-performance asymmetric induction of the Cu(I)-(R,R)-QUINOXP* complex. Finally, the method is used for the synthesis of new chiral phosphine-olefin compounds built on a cyclopropane skeleton, one of which serves as a wonderful ligand in Rh-catalyzed asymmetric conjugate addition of phenylboronic acid to various α,β-unsaturated compounds.

An expedient synthesis of highly functionalized 1,3-dienes by employing cyclopropenes as C4 units

An efficient method has been described to synthesize dicarbonyl functionalized 1,3-dienes by cleaving the C[double bond, length as m-dash]C bond of enaminones with cyclopropenes in the presence of a rhodium catalyst. The acetate-substituted cyclopropenes are judiciously chosen as standard C4 units of 1,3-diene precursors. The reactions are believed to undergo a unique cutting and insertion process, involving a C[double bond, length as m-dash]C bond cleavage of the enaminone and insertion of a new C(sp2) source with the formation of two C-C single bonds. A broad range of substrates can be used to synthesize the corresponding 1,3-dienes under very mild reaction conditions, including low catalyst-loading, ambient temperature, and a neutral reaction solvent.

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.

Thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes

An efficient and highly regio- and diastereoselective synthetic method to cyclobutane-containing spiro[2.3]hexane fused with six-membered hetero-cycles has been disclosed via a thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes. The DFT calculations indicate that this intramolecular cycloaddition proceeds in a concerted manner and account for the product selectivity. These reactions exhibited excellent yields and functional group tolerance under metal free conditions.

[3,3]-Sigmatropic Rearrangement of Cyclopropenylcarbinyl Cyanates: Access to Alkylidene(aminocyclopropane) Derivatives

Cyclopropenylcarbinyl cyanates, generated in situ by dehydration of the corresponding carbamates, underwent an efficient and stereoselective [3,3]-sigmatropic rearrangement leading to the corresponding alkylidene(isocyanatocyclopropanes), which could be converted into various alkylidene(aminocyclopropane) derivatives in a one-pot manner. This transformation complements the repertoire of sigmatropic rearrangements involving cyclopropenylcarbinol derivatives and in particular, the previously reported Overman rearrangement of cyclopropenylcarbinyl trichloroacetimidates.

Zirconocene-Mediated Selective C-C Bond Cleavage of Strained Carbocycles: Scope and Mechanism

Several approaches using organozirconocene species for the remote cleavage of strained three-membered ring carbocycles are described. ω-Ene polysubstituted cyclopropanes, alkylidenecyclopropanes, ω-ene spiro[2.2]pentanes, and ω-ene cyclopropyl methyl ethers were successfully transformed into stereodefined organometallic intermediates, allowing an easy access to highly stereoenriched acyclic scaffolds in good yields and, in most cases, excellent selectivities. DFT calculations and isotopic labeling experiments were performed to delineate the origin of the obtained chemo- and stereoselectivities, demonstrating the importance of microreversibility.

Rhodium(II)-catalyzed intramolecular cycloisomerizations of methylenecyclopropanes with N-sulfonyl 1,2,3-triazoles

A novel rhodium(II)-catalyzed tandem cycloisomerization of methylenecyclopropanes (MCPs) with N-sulfonyl 1,2,3-triazoles is disclosed. The reaction produces a series of highly functionalized polycyclic N heterocycles via a rhodium imino carbene intermediate. A distinct feature of this divergent synthesis is that different types of substrates control the reaction pathways. Moreover, several interesting transformations of these products to construct diazabicyclo[3.2.1]octane derivatives are also reported.

Functionalized Cyclopropenes and Methylenecyclopropenes from Dianions of 3-Hydroxymethylcyclopropenes

1,2-Disubstituted-3-hydroxymethylcyclopropene derivatives have been synthesized by reacting the dianions of 1-alkyl-3-hydroxymethylcyclopropenes with a range of electrophiles. Additionally, a complementary procedure is described for one-pot sequential alkylation/rearrangement to provide a convenient synthesis of a chiral methylenecyclopropane directly from a 1-alkyl-3-hydroxymethylcyclopropene.

Facially selective Cu-catalyzed carbozincation of cyclopropenes using arylzinc reagents formed by sequential I/Mg/Zn exchange

Described is a Cu-catalyzed directed carbozincation of cyclopropenes with organozinc reagents prepared by I/Mg/Zn exchange. This protocol broadens the scope with respect to functional group tolerance and enables use of aryl iodide precursors, rather than purified diorganozinc precursors. Critical to diastereoselectivity of the carbozincation step is the removal of magnesium halide salts after transmetalation with ZnCl(2).

Recent developments of cyclopropene chemistry

This critical review discusses recent developments in the field of cyclopropene chemistry. Although several excellent reviews that mainly focused on the thermolysis and pyrolysis as well as metal-mediated reactions of cyclopropenes have been published, significant new developments have also been achieved in recent years. This brand new review provides an overview of the progress from 2007 to 2011 on the syntheses and transformations of cyclopropenes as well as their related mechanistic studies (238 references).

Selectivity in metal-catalyzed carbon-carbon bond cleavage of alkylidenecyclopropanes

When more complex system leads to simpler reactivity profile; the ring-opening of strained three-membered rings such as methylene- and alkylidenecyclopropanes generally lead to several products. If one starts with more functionalized carbon skeletons, selective reactions are now observed and rationalization as well as synthetic applications are described in this concept article. This methodology could be used to the preparation of challenging structural motifs possessing quaternary carbon stereocenters in acyclic systems.

Stereospecific synthesis of alkylidenecyclopropanes via sequential cyclopropene carbomagnesation/1,3-carbon shift

Alkylidenecyclopropanes can be synthesized from enantiomerically enriched cyclopropene derivatives with >99% stereotransfer and good to excellent yield. The protocol comprises the stereoselective reaction of Grignard reagents with 1-alkoxymethyl-3-hydroxymethylcyclopropenes and a stereospecific [1,3] carbon shift reaction.