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, β-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.

Cobalt­(II) halides in combination with phenoxyimine (FI) ligands generated efficient precatalysts in situ for the C­(sp2)–C­(sp3) Suzuki–Miyaura cross-coupling between alkyl bromides and neopentylglycol (hetero)­arylboronic esters. The protocol enabled efficient C–C bond formation with a host of nucleophiles and electrophiles (36 examples, 34–95%) with precatalyst loadings of 5 mol %. Studies with alkyl halide electrophiles that function as radical clocks support the intermediacy of alkyl radicals during the course of the catalytic reaction. The improved performance of the FI–cobalt catalyst was correlated with decreased lifetimes of cage-escaped radicals as compared to those of diamine-type ligands. Studies of the phenoxyimine–cobalt coordination chemistry validate the L,X interaction leading to the discovery of an optimal, well-defined, air-stable mono-FI–cobalt­(II) precatalyst structure.

The ability to understand and predict reactivity is essential for the development of new reactions. In the context of Ni-catalyzed C­(sp3)–O functionalization, we have developed a unique strategy employing activated cyclopropanols to aid the design and optimization of a redox-active leaving group for C­(sp3)–O arylation. In this chemistry, the cyclopropane ring acts as a reporter of leaving-group reactivity, since the ring-opened product is obtained under polar (2e) conditions, and the ring-closed product is obtained under radical (1e) conditions. Mechanistic studies demonstrate that the optimal leaving group is redox-active and are consistent with a Ni­(I)/Ni­(III) catalytic cycle. The optimized reaction conditions are also used to synthesize a number of arylcyclopropanes, which are valuable pharmaceutical motifs.

Herein, we report a Ni-catalyzed reductive coupling for the synthesis of benzonitriles from aryl (pseudo)halides and an electrophilic cyanating reagent, 2methyl-2-phenyl malononitrile (MPMN). MPMN is a bench-stable, carbon-bound electrophilic CN reagent that does not release cyanide under the reaction conditions. A variety of medicinally relevant benzonitriles can be made in good yields. Addition of NaBr to the reaction mixture allows for the use of more challenging aryl electrophiles such as aryl chlorides, tosylates, and triflates. Mechanistic investigations suggest that NaBr plays a role in facilitating oxidative addition with these substrates.

Metal homoenolates, produced via C-C bond cleavage of cyclopropanols, have been extensively investigated as nucleophiles for the synthesis of β-substituted carbonyl derivatives. Herein, we demonstrate that zinc homoenolates can react as carbonyl-electrophiles in the presence of nucleophilic amines to yield highly valuable trans-cyclopropylamines in good yields and high diastereoselectivities. GSK2879552, a lysine demethylase 1 inhibitor currently in clinical trials for the treatment of small cell lung carcinoma, was synthesized using this strategy.