Reaction of α-halo organoindium reagents with carbonyl compounds and electron-deficient alkenes

The Rapid Synthesis of Colibactin Warhead Model Compounds Using New Metal-Free Photocatalytic Cyclopropanation Reactions Facilitates the Investigation of Biological Mechanisms

Herein, we report the synthesis of a series of colibactin warhead model compounds using two newly developed metal-free photocatalytic cyclopropanation reactions. These mild cyclopropanations expand the known applications of eosin within synthesis. A halogen atom transfer reaction mode has been harnessed so that dihalides can be used as the cyclopropanating agents. The colibactin warhead models were then used to provide new insight into two key mechanisms in colibactin chemistry. An explanation is provided for why the colibactin warhead sometimes undergoes a ring expansion-addition reaction to give fused cyclobutyl products while at other times nucleophiles add directly to the cyclopropyl unit (as when DNA adds to colibactin). Finally, we provide some evidence that Cu(II) chelated to colibactin may catalyze an important oxidation of the colibactin-DNA adduct. The Cu(I) generated as a result could then also play a role in inducing double strand breaks in DNA.

Photoredox catalysis harvesting multiple photon or electrochemical energies

Photoredox catalysis (PRC) is a cutting-edge frontier for single electron-transfer (SET) reactions, enabling the generation of reactive intermediates for both oxidative and reductive processes via photon activation of a catalyst. Although this represents a significant step towards chemoselective and, more generally, sustainable chemistry, its efficacy is limited by the energy of visible light photons. Nowadays, excellent alternative conditions are available to overcome these limitations, harvesting two different but correlated concepts: the use of multi-photon processes such as consecutive photoinduced electron transfer (conPET) and the combination of photo- and electrochemistry in synthetic photoelectrochemistry (PEC). Herein, we review the most recent contributions to these fields in both oxidative and reductive activations of organic functional groups. New opportunities for organic chemists are captured, such as selective reactions employing super-oxidants and super-reductants to engage unactivated chemical feedstocks, and scalability up to gram scales in continuous flow. This review provides comparisons between the two techniques (multi-photon photoredox catalysis and PEC) to help the reader to fully understand their similarities, differences and potential applications and to therefore choose which method is the most appropriate for a given reaction, scale and purpose of a project.

Diethylzinc-Mediated Cross-Coupling Reactions between Dibromoketones and Monobromo Carbonyl Compounds

A novel route to synthesize 1,4-dicarbonyl compounds is described. α,α-Dibromoketones generate zinc enolates through a diethylzinc-mediated halogen-metal exchange and react with α-bromocarbonyl compounds to furnish 1,4-dicarbonyl compounds via a second generation of zinc enolates. This cross-coupling reaction is enabled by the chemoselective formation of zinc enolates from α,α-dibromoketones in the presence of α-bromocarbonyl compounds. Chiral 1,4-dicarbonyl compounds can be obtained via the enantioselective bromination of aldehydes using a chiral secondary amine catalyst and a subsequent cross-coupling reaction between the resulting chiral α-bromoaldehydes and α,α-dibromoacetophenones.

Facile and practical hydrodehalogenations of organic halides enabled by calcium hydride and palladium chloride

For the first time, calcium hydride and palladium chloride were used to reduce a wide range of organic halides including aromatic bromides, aromatic chlorides, aromatic triflates, aliphatic bromides, aliphatic chlorides and trihalomethyl compounds.

Direct catalytic enantioselective Mannich-type reaction of dichloroacetonitrile using bis(imidazoline)-Pd catalysts

The catalytic enantioselective Mannich-type reaction of dichloroacetonitrile with imines has been developed.

Regioselective dihalohydration reactions of propargylic alcohols: gold-catalyzed and noncatalyzed reactions

The regioselective conversion of propargylic alcohols into previously unreported α,α-diiodo-β-hydroxyketones was achieved by treatment with N-iodosuccinimide in the presence of a gold catalyst. The corresponding α,α-dichloro-β-hydroxyketones were obtained by treatment with trichloroisocyanuric acid in the absence of a catalyst. The latter reaction can be extended to other alkynols. These transformations can be used to prepare potentially useful halogenated building blocks. Preliminary mechanistic studies suggest that the reaction involves participation of the acetonitrile solvent in the formation of a 5-halo-1,3-oxazine intermediate.

Preparation of gamma-Heterosubstituted Allylindium and Diindium Reagents and Their Reactions with Carbonyl Compounds

Various gamma-heteroatom-substituted allylindium reagents were prepared, and their reactions with carbonyl compounds were examined. The reaction of 1,3-dibromopropene with metallic indium gave two types of organoindium species, gamma-bromoallylindium and allylic diindium reagents. While the former gave 2-phenyl-3-vinyloxirane upon the coupling with benzaldehyde, the latter gave 1-phenylbut-3-en-1-ol. 1-Iodo-3-bromopropene gave the homoallylic alcohol exclusively. gamma-Alkoxyallylindium reagents were prepared by treating the corresponding gamma-alkoxyallyllithium with indium trichloride and reacted with benzaldehyde to give vic-diol mono ethers in high yields with good syn selectivity. gamma-(Trimethylsilyl)allylindium and alpha,gamma-disubstituted allylindium reagents were also prepared via transmetalation with the corresponding allyllithium.