Chien-Wei Chiang

Anti-Markovnikov Oxidation of β-Alkyl Styrenes with H2O as the Terminal Oxidant.

Oxygenation of alkenes is one of the most straightforward routes for the construction of carbonyl compounds. Wacker oxidation provides a broadly useful strategy to convert the mineral oil into higher value-added carbonyl chemicals. However, the conventional Wacker chemistry remains problematic, such as the poor activity for internal alkenes, the lack of anti-Markovnikov regioselectivity, and the high cost and chemical waste resulted from noble metal catalysts and stoichiometric oxidant. Here, we describe an unprecedented dehydrogenative oxygenation of β-alkyl styrenes and their derivatives with water under external-oxidant-free conditions by utilizing the synergistic effect of photocatalysis and proton-reduction catalysis that can address these challenges. This dual catalytic system possesses the single anti-Markovnikov selectivity due to the property of the visible-light-induced alkene radical cation intermediate.

Characterization of a paramagnetic mononuclear nonheme iron-superoxo complex

O2 bubbling into a THF solution of FeII(BDPP) (1) at −80 °C generates a reversible bright yellow adduct 2. Characterization by resonance Raman and Mössbauer spectroscopy provides complementary insights into the nature of 2. The former shows a resonance-enhanced vibration at 1125 cm–1, which can be assigned to the ν(O–O) of a bound superoxide, while the latter reveals the presence of a high-spin iron(III) center that is exchange-coupled to the superoxo ligand, like the FeIII–O2– pair found for the O2 adduct of 4-nitrocatechol-bound homoprotocatechuate 2,3-dioxygenase. Lastly, 2 oxidizes dihydroanthracene to anthracene, supporting the notion that FeIII–O2– species can carry out H atom abstraction from a C–H bond to initiate the 4-electron oxidation of substrates proposed for some nonheme iron enzymes.

Markovnikov-Selective Radical Addition of S-Nucleophiles to Terminal Alkynes through a Photoredox Process

Direct radical additions to terminal alkynes have been widely employed in organic synthesis, providing credible access to the anti-Markovnikov products. Because of the Kharasch effect, regioselective control for the formation of Markovnikov products still remains a great challenge. Herein, we develop a transition-metal-free, visible light-mediated radical addition of S-nucleophiles to terminal alkynes, furnishing a wide array of α-substituted vinyl sulfones with exclusive Markovnikov regioselectivity. Mechanistic investigations demonstrated that radical/radical cross-coupling might be the key step in this transformation. This radical Markovnikov addition protocol also provides an opportunity to facilitate the synthesis of other valuable α-substituted vinyl compounds.

Highly enantioselective Rh-catalyzed alkenylation of imines: synthesis of chiral allylic amines via asymmetric addition of potassium alkenyltrifluoroborates to N-tosyl imines.

For the first time, simple N-tosyl aryl aldimines, prepared from the condensation of tosyl amide and aromatic aldehydes, can be used as substrates in the rhodium catalyzed 1,2-addition reaction using alkenylboron nucleophiles. In the presence of 1.5 mol % of [RhCl(1e)]2, enantioselective addition of various potassium alkenyltrifluoroborates to aryl aldimines furnished the corresponding chiral allylic amines in 73-96% yield and 72->99.5% ee. Notably, this method efficiently provides the di-, tri-, and tetrasubstituted allylic N-tosyl amines with high asymmetric induction.

Rhodium-Catalyzed Asymmetric Addition of Arylboronic Acids to β-Nitroolefins: Formal Synthesis of (S)-SKF 38393

An efficient enantioselective addition of an array of arylboronic acids to various β-nitrostyrenes catalyzed by a novel and reactive rhodium-diene catalyst (S/C up to 1000) was developed, providing β,β-diarylnitroethanes in good to high yields (62-99%) with excellent enantioselectivities (85-97% ee). The method was extended to 2-heteroarylnitroolefins and 2-alkylnitroolefins similarly providing the desired products with high enantioselectivities and yields. The usefulness of this method was demonstrated in the formal synthesis of the enantiomer of the dopamine receptor agonist and antagonist, SKF 38393.

Catalyst‐Free Difunctionalization of Activated Alkenes in Water: Efficient Synthesis of β‐Keto Sulfides and Sulfones

Difunctionalization of activated alkenes, a powerful strategy in chemical synthesis, has been accomplished for direct synthesis of a series of β-keto sulfides and β-keto sulfones. The transformation, mediated by O2 , proceeds smoothly in water and without any catalyst. Prominent advantages of this method include mild reaction conditions, purification simplicity, and gram-scale synthesis, underlining the practical utility of this methodology.

A Discrete Five‐Coordinate NiIII Complex Resembling the Active Site of the Oxidized Form of Nickel Superoxide Dismutase

Superoxide anion (O2 ), an unavoidable byproduct in aerobic organisms, can cause irreversible cellular damage. To suppress such oxidative stress three classes of superoxide dismutase (SOD) have evolved in various organisms: 1) CuZnSOD, 2) FeSOD or MnSOD, and 3) NiSOD. The Ni-containing superoxide dismutase (NiSOD) discovered recently from Streptomyces species and marine cyanobacteria can catalyze the disproportionation of O2 into O2 and H2O2 through a cycle of Ni II and Ni oxidation states (Scheme 1). The X-ray structure of the reduced NiSOD re-

From Anilines to Quinolines: Iodide‐ and Silver‐Mediated Aerobic Double C−H Oxidative Annulation–Aromatization

Quinoline synthesis from easily accessible raw materials such as anilines is a valuable and meaningful task. Herein, we communicate an iodide- and silver-mediated C-H/C-H oxidative annulation-aromatization between anilines and allyl alcohols. This protocol provides a direct route to the synthesis of quinoline derivatives from inexpensive commodities. Various kinds of anilines, even heterocyclic anilines, were shown to be workable substrates, generating the corresponding multi-substituted quinolines in good yields.

Synthesis and Characterization of NiIIIN3S2 Complexes as Active Site Models for the Oxidized Form of Nickel Superoxide Dismutase

Nickel complexes, [Ni(H2BA(R)TPP)](ClO4)2 (R = Ph for 1 or iPr for 2), supported by a pentadentate ligand H2BA(R)TPP were synthesized and oxidized to form Ni(III) species having a N3S2 coordination environment to mimic the active site of the oxidized form of nickel superoxide dismutase (NiSODox). The Ni(III) species 2(+) exhibited a rhombic signal with g values at 2.15, 2.12 and 2.02 similar to that of NiSODox. DFT calculations revealed that 2(+) has an unpaired electron primarily located in the dz2 orbital of the Ni(III) center, which strongly overlaps with the pz orbital of the axial pyridine nitrogen of H2BA(Pr)TPP.

From Ketones, Amines, and Carbon Monoxide to 4-Quinolones: Palladium-Catalyzed Oxidative Carbonylation

A novel method of palladium-catalyzed oxidative carbonylation of ketones, amines, and carbon monoxide for the synthesis of 4-quinolones has been developed. This protocol provides a straightforward route to construct useful 4-quinolone derivatives from inexpensive chemicals.