Pinhong Chen

Copper‐Catalyzed Intermolecular Trifluoromethylazidation of Alkenes: Convenient Access to CF3‐Containing Alkyl Azides

A novel copper-catalyzed intermolecular trifluoromethylazidation of alkenes has been developed under mild reaction conditions. A variety of CF3 -containing organoazides were directly synthesized from a wide range of olefins, including activated and unactivated alkenes, and the resulting products can be easily transformed into the corresponding CF3 -containing amine derivatives.

Copper-Catalyzed Intermolecular Trifluoromethylarylation of Alkenes: Mutual Activation of Arylboronic Acid and CF3+ Reagent

A novel copper-catalyzed intermolecular trifluoromethylarylation of alkenes is developed using less active ether-type Tognis reagent under mild reaction conditions. Various alkenes and diverse arylboronic acids are compatible with these conditions. Preliminary mechanistic studies reveal that a mutual activation process between arylboronic acid and CF3(+) reagent is essential. In addition, the reaction might involve a rate-determining transmetalation, and the final aryl C-C bond is derived from reductive elimination of the aryl(alkyl)Cu(III) intermediate.

Selective Inhibitors of Histone Methyltransferase DOT1L: Design, Synthesis, and Crystallographic Studies

Histone H3-lysine79 (H3K79) methyltransferase DOT1L plays critical roles in normal cell differentiation as well as initiation of acute leukemia. We used structure- and mechanism-based design to discover several potent inhibitors of DOT1L with IC(50) values as low as 38 nM. These inhibitors exhibit only weak or no activities against four other representative histone lysine and arginine methyltransferases, G9a, SUV39H1, PRMT1 and CARM1. The X-ray crystal structure of a DOT1L-inhibitor complex reveals that the N6-methyl group of the inhibitor, located favorably in a predominantly hydrophobic cavity of DOT1L, provides the observed high selectivity. Structural analysis shows that it will disrupt at least one H-bond and/or have steric repulsion for other histone methyltransferases. These compounds represent novel chemical probes for biological function studies of DOT1L in health and disease.

Enantioselective cyanation of benzylic C–H bonds via copper-catalyzed radical relay

Direct methods for stereoselective functionalization of sp3-hybridized carbon–hydrogen [C(sp3)–H] bonds in complex organic molecules could facilitate much more efficient preparation of therapeutics and agrochemicals. Here, we report a copper-catalyzed radical relay pathway for enantioselective conversion of benzylic C–H bonds into benzylic nitriles. Hydrogen-atom abstraction affords an achiral benzylic radical that undergoes asymmetric C(sp3)–CN bond formation upon reaction with a chiral copper catalyst. The reactions proceed efficiently at room temperature with the benzylic substrate as limiting reagent, exhibit broad substrate scope with high enantioselectivity (typically 90 to 99% enantiomeric excess), and afford products that are key precursors to important bioactive molecules. Mechanistic studies provide evidence for diffusible organic radicals and highlight the difference between these reactions and C–H oxidations mediated by enzymes and other catalysts that operate via radical rebound pathways.

Palladium-catalyzed cascade C-H trifluoroethylation of aryl iodides and Heck reaction: efficient synthesis of ortho-trifluoroethylstyrenes.

A palladium-catalyzed selective C-H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho-trifluoroethyl-substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd(IV) intermediate, which is generated through the rate-determining oxidative addition of CF3CH2I to a palladacycle; the bulky nature of CF3CH2I influences the reactivity. Reductive elimination from the Pd(IV) complex then leads to the formation of the aryl-CH2CF3 bond.

Highly Selective Pd-Catalyzed Intermolecular Fluorosulfonylation of Styrenes

A novel Pd-catalyzed intermolecular regio- and diastereoselective fluorosulfonylation of styrenes has been developed under mild conditions. This reaction exhibits a wide range of functional-group tolerance in styrenes and arylsulfinic acids to afford various β-fluoro sulfones. Preliminary mechanistic study reveals an unusual mechanism, in which a high-valent L2Pd(III)F species side-selectively reacts with a benzylic carbon radical to deliver a C-F bond. This pathway is distinct from a previously reported radical fluorination reaction.

Copper-Catalyzed Trifluoromethylthiolation of Aryl Halides with Diverse Directing Groups

The expansion of cross-coupling components in Cu-catalyzed C-X bond forming reactions have received much attention recently. A novel Cu-catalyzed trifluoromethylthiolation of aryl bromides and iodides with the assistance of versatile directing groups such as pyridyl, methyl ester, amide, imine and oxime was reported. CuBr was used as the catalyst, and 1,10-phenanthroline as the ligand. By changing the solvent from acetonitrile to DMF, the coupling process could even take place at room temperature.

Pd-Catalyzed Intramolecular Aminohydroxylation of Alkenes with Hydrogen Peroxide as Oxidant and Water as Nucleophile

A palladium-catalyzed intramolecular aminohydroxylation of alkenes was developed, in which H2O2 was applied as the sole oxidant. A variety of related alkyl alcohols could be successfully obtained with good yields and excellent diastereoselectivities, which directly derived from oxidation cleavage of alkyl C-Pd bond by H2O2. Facile transformation of these products provided a powerful tool toward the synthesis of 2-amino-1,3-diols and 3-ol amino acids. Preliminary mechanistic studies revealed that major nucleophilic attack of water (S(N)2 type) at high-valent Pd center contributes to the final C-O(H) bond formation.

Palladium-Catalyzed Intramolecular Aminotrifluoromethoxylation of Alkenes.

The first catalytic trifluoromethoxylation of unactivated alkenes has been developed, in which Pd(CH3CN)2Cl2 was used as catalyst, AgOCF3 as trifluoromethoxide source, and Selectfluor-BF4 as oxidant. A variety of 3-OCF3 substituted piperidines were selectively obtained in good yields. Direct evidence was provided to address the facile reductive elimination of Pd(IV)-OCF3 complex to form sp(3) C-OCF3 bond.

Copper‐Catalyzed Regioselective Fluorination of Allylic Halides

Group activity: A novel copper-catalyzed fluorination of internal allylic bromides and chlorides has been developed by using Et3N⋅3u2009HF as the fluorine source. A functional group (FG) within the substrate is required to achieve the allylic fluorination, and a variety of secondary allylic fluoride compounds can be accessed in good yield with excellent regioselectivity.