Late Transition Metal-Mediated Formation of Carbon–Halogen Bonds. In: Vigalok A, editor. C-X Bond Formation. Berlin: Springer Berlin Heidelberg; 2010. pp. 19-38. [DOI: 10.1007/978-3-642-12073-2_2]

Enantioselective Desymmetrization of Methylenedianilines via Enzyme-Catalyzed Remote Halogenation

Extensive effort has been devoted to engineering flavin-dependent halogenases (FDHs) with improved stability, expanded substrate scope, and altered regioselectivity. Here, we show that variants of rebeccamycin halogenase (RebH) catalyze enantioselective desymmetrization of methylenedianilines via halogenation of these substrates distal to their pro-stereogenic center. Structure-guided engineering was used to increase the conversion and selectivity of these reactions, and the synthetic utility of the halogenated products was shown via conversion of to a chiral α-substituted indole. These results constitute the first reported examples of asymmetric catalysis by FDHs.

An efficient synthesis of versatile synthon 3-chlorooxindoles with NaCl/oxone

The present work describes an expedient approach for the direct conversion of indole-3-carboxaldehyde to 3-chlorooxindoles.

Metal-free synthesis of N-fused heterocyclic iodides via C-H functionalization mediated by tert-butylhydroperoxide

Direct, regioselective and metal-free synthesis of fused N-heterocyclic iodides is reported. This regioselective C-H functionalization is mediated by tert-butylhydroperoxide (TBHP), via dual activation of molecular iodine and a heterocyclic substrate, resulting in the in situ generation of electrophilic iodine species (I(+)), and free radical(s) (t)BuO˙ or (t)BuOO˙, driving the iodination reaction.

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

Ligand-Enabled Stereoselective β-C(sp(3))-H Fluorination: Synthesis of Unnatural Enantiopure anti-β-Fluoro-α-amino Acids

A quinoline-based ligand was shown to promote palladium-catalyzed β-C(sp(3))-H fluorination for the first time. A range of unnatural enantiopure fluorinated α-amino acids were obtained through sequential β-C(sp(3))-H arylation and subsequent stereoselective fluorination from readily available L-alanine.

Anion-Dependent Switch in C-X Reductive Elimination Diastereoselectivity

Reaction of a complex Pt organometallic species with electrophilic halogen sources in the presence of X- ligands changes the mechanism of reductive elimination from a concerted reductive coupling type to an SN2 type reductive elimination. In the absence of the added X- ligand the reductive elimination is stereoretentive; in its presence, the process is stereoinvertive. This selectivity hinges on the reactivity of a key five-coordinate Pt(IV) intermediate with the X- ligand.

Catalytic enantioselective cyclization and C3-fluorination of polyenes

(Xylyl-phanephos)Pt(2+) in combination with XeF(2) mediates the consecutive diastereoselective cation-olefin cyclization/fluorination of polyene substrates. Isolated yields were typically in the 60-69% range while enantioselectivities reached as high as 87%. The data are consistent with a stereoretentive fluorination of a P(2)Pt-alkyl cation intermediate.

Carbon(sp(3))-fluorine bond-forming reductive elimination from palladium(IV) complexes

Pd(IV)-fluoride complexes, some of which are remarkably insensitive to water, have been synthesized and used in the title reaction, which proceeds with high selectivity to give the product of the C(sp(3))-F coupling. Preliminary mechanistic studies implicate a pathway involving dissociation of pyridine followed by direct C-F coupling at the Pd center.

Nucleophilic aryl fluorination and aryl halide exchange mediated by a Cu(I)/Cu(III) catalytic cycle

Copper-catalyzed halide exchange reactions under very mild reaction conditions are described for the first time using a family of model aryl halide substrates. All combinations of halide exchange (I, Br, Cl, F) are observed using catalytic amounts of Cu(I). Strikingly, quantitative fluorination of aryl-X substrates is also achieved catalytically at room temperature, using common F(-) sources, via the intermediacy of aryl-Cu(III)-X species. Experimental and computational data support a redox Cu(I)/Cu(III) catalytic cycle involving aryl-X oxidative addition at the Cu(I) center, followed by halide exchange and reductive elimination steps. Additionally, defluorination of the aryl-F model system can be also achieved with Cu(I) at room temperature operating under a Cu(I)/Cu(III) redox pair.

Electrophilic fluorination of cationic Pt-aryl complexes

The electrophilic fluorination of several (triphos)Pt-aryl(+) establishes the first example of aryl-F coupling from a Pt center.