Selective Carbon-Carbon Bond Cleavage of Cyclopropanols.

The carbon-carbon (C-C) bond cleavage of cyclopropanols is a wide area of research with much current activity. This review highlights new developments in this area over the past two decades. A summary is made of the three main reactivity modes, namely, homoenolate chemistry, ß-keto radical chemistry, and acid-catalyzed ring-opening, as well as all other methods for the C-C bond cleavage and functionalization of cyclopropanols, including base-mediated ring-opening, metal-catalyzed C-C insertions and eliminations, oxidative fragmentation using hypervalent iodine reagents, reactions of donor-acceptor cyclopropanols, and pericylic reactions. Emphasis is placed on the synthetic utility of cyclopropanols and related derivatives, which have emerged as unique three-carbon synthons.

Synthesis of Nitrile-Bearing Quaternary Centers by an Equilibrium-Driven Transnitrilation and Anion-Relay Strategy.

The efficient preparation of nitrile-containing building blocks is of interest due to their utility as synthetic intermediates and their prevalence in pharmaceuticals. As a result, significant efforts have been made to develop methods to access these motifs which rely on safer and non-toxic sources of CN. Herein, we report that 2-methyl-2-phenylpropanenitrile is an efficient, non-toxic, electrophilic CN source for the synthesis of nitrile-bearing quaternary centers by a thermodynamic transnitrilation and anion-relay strategy. This one-pot process leads to nitrile products resulting from the gem-difunctionalization of alkyl lithium reagents.

Ni-Catalyzed Reductive 1,2-Alkylarylation of Alkenes for the Synthesis of Spirocyclic γ-Lactams.

An intermolecular nickel-catalyzed reductive 1,2-alkylarylation of acrylates with cyclopropylamine NHP esters and aryl iodides is reported. This operationally simple protocol provides direct access to 1-alkylcyclopropylamine scaffolds. The mild conditions are compatible with four-membered α-amino strained rings as well as five- and six-membered ring systems. The products undergo cyclization to access α-arylated spirocyclic γ-lactams─a motif present in several pharmaceuticals.

Safe, selective, and scalable carbenes.

The synthesis of reactive carbene intermediates is made simpler and safer.

Synthesis of 1- and 1,2-Substituted Cyclopropylamines from Ketone Homoenolates.

Ketone homoenolates are intermediates with both nucleophilic and electrophilic properties. While there are several reports on their use as nucleophiles, there are few reports on their potential as electrophiles. Herein, we report the use of ketone zinc/copper homoenolates as electrophiles in the synthesis of 1- and 1,2-substituted cyclopropylamines. We found that CuCN·2LiCl is essential to produce a more reactive homoenolate intermediate. We also report a facile telescoped sequence from ß-substituted enones toward 1,2-disubstituted cyclopropylamines.

Ni-Catalyzed Reductive Cross-Coupling of Cyclopropylamines and Other Strained Ring NHP Esters with (Hetero)Aryl Halides.

A nickel-catalyzed reductive cross-coupling of cyclopropylamine NHP esters with (hetero)aryl halides is reported. This efficient protocol provides direct access to 1-arylcyclopropylamines, a bioisosteric motif commonly used in small molecule drug discovery. The reaction proceeds rapidly (<2 h) with excellent functional group tolerance and without requiring heat- or air-sensitive reagents. The method can also be extended to the arylation of four-membered strained rings. The NHP esters are easily obtained from the corresponding commercially available carboxylic acids in one step with high yields and no column chromatography.

Synthesis of trans-2-Substituted Cyclopropylamines from α-Chloroaldehydes.

Cyclopropylamines are prevalent in pharmaceuticals and agrochemicals. Herein, we report the synthesis of trans-2-substituted cyclopropylamines in high diastereoselectivity from readily available α-chloroaldehydes. The reaction proceeds via trapping of an electrophilic zinc homoenolate with an amine followed by ring closure to generate the cyclopropylamine. We have also observed that cyclopropylamine cis/trans-isomerization occurs in the presence of zinc halide salts and that this process can be turned off by the addition of a polar aprotic cosolvent.