Search

Featuring the simultaneous generation of a library of compounds from a certain intermediate, divergent synthesis has found increasing applications in the construction of natural products and potential medicines. Inspired by this approach, presented herein is a general strategy to introduce functionality, in a divergent manner, into covalent organic frameworks (COFs). This modular protocol includes two stages of covalent assembly, through which functional COFs can be constructed by a three‐step transformation of a key platform molecule, such as 4,7‐dibromo‐2‐chloro‐1H‐benzo[d]imidazole (DBCBI). Constructed herein are four types of chiral COFs (CCOFs) from DBCBI by nucleophilic substitution, Suzuki coupling, and imine formation. The unique array of eight isoframework CCOFs allowed investigation of their catalytic performance and structure–activity relationship in an asymmetric amination reaction. [ABSTRACT FROM AUTHOR]

We report the first example of RhII-catalyzed chemoselective double C(sp3)H oxygenation, which can directly transform various toluene derivatives into highly valuable aromatic aldehydes with great chemoselectivity and practicality. The critical combination of catalyst Rh(OAc)2, oxidant Selectfluor, and solvents of TFA/TFAA promises the successful delivery of the oxidation with satisfactory yields. A possible mechanism involving a unique carbene-Rh complex is proposed, and has been supported by both experiments and theoretical calculations. [ABSTRACT FROM AUTHOR]

We report herein a highly efficient palladium‐catalyzed carbene insertion into strained Si−C bonds of benzosilacyclobutanes, which provides an efficient method to access α‐chiral silanes. With a sterically hindered ligand, carbene insertion into the C(sp3)−Si bond of benzosilacyclobutanes occurred in excellent site‐ and enantioselectivity, while C(sp2)−Si bond insertion occurred selectively with less sterically hindered ligands. Reaction mechanism, in particular the roles of the chiral ligands in controlling the site‐selectivity of the insertion reactions, are elucidated by using hybrid density functional theory. [ABSTRACT FROM AUTHOR]

Higher‐order cycloadditions, particularly [8+2] cycloadditions, are a straightforward and efficient strategy for constructing significant medium‐sized architectures. Typically, configuration‐restrained conjugated systems are utilized as 8π‐components for higher‐order concerted cycloadditions. However, for this reason, 10‐membered monocyclic skeletons have never been constructed via catalytic asymmetric [8+2] cycloaddition with high peri‐ and stereoselectivity. Here, we accomplished an enantioselective [8+2] dipolar cycloaddition via the merger of visible‐light activation and asymmetric palladium catalysis. This protocol provides a new route to 10‐membered monocyclic architectures bearing chiral quaternary stereocenters with high chemo‐, peri‐, and enantioselectivity. The success of this strategy relied on the facile in situ generation of Pd‐containing 1,8‐dipoles and their enantioselective trapping by ketene dipolarophiles, which were formed in situ via a photo‐Wolff rearrangement. [ABSTRACT FROM AUTHOR]

Higher‐order cycloadditions, particularly [8+2] cycloadditions, are a straightforward and efficient strategy for constructing significant medium‐sized architectures. Typically, configuration‐restrained conjugated systems are utilized as 8π‐components for higher‐order concerted cycloadditions. However, for this reason, 10‐membered monocyclic skeletons have never been constructed via catalytic asymmetric [8+2] cycloaddition with high peri‐ and stereoselectivity. Here, we accomplished an enantioselective [8+2] dipolar cycloaddition via the merger of visible‐light activation and asymmetric palladium catalysis. This protocol provides a new route to 10‐membered monocyclic architectures bearing chiral quaternary stereocenters with high chemo‐, peri‐, and enantioselectivity. The success of this strategy relied on the facile in situ generation of Pd‐containing 1,8‐dipoles and their enantioselective trapping by ketene dipolarophiles, which were formed in situ via a photo‐Wolff rearrangement. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were employed to elucidate the mechanism of Mn‐catalyzed chemoselective hydroarylation reactions. The Mn‐catalyzed [4+2] annulation undergoes a reaction pathway involving sequential imine‐directed C−H bond cleavage, alkyne insertion into the Mn−C bond, β‐oxygen elimination and outer catalytic cycle annulation–aromatization. Computational results demonstrated that the previously proposed chelation‐assisted alkyne insertion process was unfavorable owing to the weak coordination ability of the β‐oxygen leaving group compared with that of CO. Further noncovalent interactions analysis indicated that the origin of the high regioselectivity was contributed to the steric repulsion resulting from significant nonbonding overlap between the reacting aryl moiety and the quaternary carbon group of the reactant in the alkyne insertion step. In addition, in the Brønsted‐acid‐mediated chemoselective alkenylation reaction, the used terminal alkynes had relatively enhanced reactivity in the alkyne insertion step owing to its reduced steric repulsion. From the active alkenyl‐Mn intermediate, the activation free energy of protonation and β‐oxygen elimination are approximate, thus the alkenylated product is obtained after protonation in an acidic system. We expect that this detailed mechanistic study will significantly enhance our ability to develop Mn‐catalyzed arene C−H bond functionalization reactions. Clarity, form, and function: Density functional theory calculations were employed to elucidate the mechanism of Mn‐catalyzed chemoselective hydroarylation reactions. The Mn‐catalyzed [4+2] annulation undergoes a reaction pathway involving sequential imine‐directed C−H bond cleavage, alkyne insertion into the Mn−C bond, β‐oxygen elimination and outer catalytic cycle annulation–aromatization. [ABSTRACT FROM AUTHOR]

Although zinc catalysis is widely used in organic synthesis, very few studies on the dinuclear zinc mechanism have been reported. Here, a dinuclear zinc pathway is proposed for the Zn(OTf)2-catalyzed oxidative coupling of aldehydes with terminal alkynes. DFT calculations revealed that the deprotonation of the terminal alkyne would preferentially lead to the formation of a dinuclear zinc intermediate. The nucleophilic addition of this intermediate to an aldehyde, followed by an Oppenauer-type oxidation was investigated theoretically according to the mono- and dinuclear pathways. The formation of a dinuclear zinc intermediate from a mononuclear alkynyl zinc complex was exergonic, favoring the dinuclear zinc pathway. The subsequent protonation and regeneration of the active dinuclear catalyst were also evaluated by DFT calculations. The oxidizabilities of various aldehydes and ketones were evaluated to determine the best oxidant for this step. Trifluoroacetaldehyde was predicted to be a better oxidant for this reaction because its calculated energy barrier for the Oppenauer-type oxidation step was much lower than that of the other carbonyl complexes. [ABSTRACT FROM AUTHOR]

A highly regio- and stereoselective method to construct a broad range of 7-oxabicyclo[2.2.1]heptanes, which proceeds through a sequential reaction involving gold(I)-catalyzed cycloisomerization of alkynediols and sequential semi-pinacol-type 1,2-alkyl migration, was developed. The developed chemistry was applied to the asymmetric total synthesis of the natural product farnesiferol C. [ABSTRACT FROM AUTHOR]

A diagram is presented showing the activation of rhodium-catalyst of carbon-hydrogen (C-H) of phenacyl ammonium salts helped by an oxidizing carbon nitrogen (C-N) bond.

For the first time, the influence of the alcohol on efficiency and selectivity of an asymmetric transfer hydrogenation of imines is reported. [ABSTRACT FROM AUTHOR]

An abstract of the article "Regio- and Stereoselective Syntheses of 7-Oxabicyclo[2.2.1]heptanes via a Gold(I)- - Catalyzed Cycloisomerization of Alkynediols: Asymmetric Total Synthesis of Farnesiferol C" by Yue-Qing Gu and colleagues is presented.

The utility of this method is demonstrated in the synthesis of the mycotoxin isopatulin (IV). [ABSTRACT FROM AUTHOR]

Iron-catalyzed decarboxylative [4 + 1] cycloaddition reactions are described for the first time. [ABSTRACT FROM AUTHOR]

Iodine-catalyzed oxidative cross-coupling/cyclization for the synthesis of furans and indolizines is reported. [ABSTRACT FROM AUTHOR]

A novel C-O bond formation reaction through carbon-centered radical addition to the carbonyl oxygen of amides or esters is presented. [ABSTRACT FROM AUTHOR]

A gold-catalyst with an electron-deficient phosphite as the ancillary ligand is found to exclusively promote the carbophilic chemoselective addition of arenes, hetarenes and 1,3-diketones to α-aryldiazoesters. [ABSTRACT FROM AUTHOR]

The first examples of a visible-light-mediated decarboxylation/oxidative amidation of α-keto acid with aliphatic and aromatic primary amines are described. [ABSTRACT FROM AUTHOR]