Carbene cascade reactions involving carbene/ alkyne metathesis have attracted much attention over the past decades because this chemistry offers great potential to build complicated cyclic molecules. However, the formed vinyl metal carbenoids in these reactions are limited to exocyclic carbenes, and the generation of endocyclic vinyl carbene complexes remains unexplored. Here, we report an unprecedented gold-catalyzed oxidative cyclization of terminal diynes. Importantly, the generation of endocyclic vinyl carbene complexes was involved in this oxidative cyclization, which is distinctively different from previous protocols. This method allows the facile synthesis of various valuable naphthoquinones and carbazolequinones from readily available diynes under exceptionally mild reaction conditions and features a broad substrate scope and wide functional group tolerance. Moreover, theoretical calculations provide further evidence on the divergent selectivity of this cyclization reaction.

Here, we report a copper-catalyzed asymmetric cascade cyclization/[1,2]-Stevens-type rearrangement via a non-diazo approach, leading to the practical and atomeconomic assembly of various valuable chiral chromeno [3,4c]pyrroles bearing a quaternary carbon stereocenter in generally moderate to good yields with wide substrate scope and excellent enantioselectivities (up to 99 % ee). Importantly, this protocol not only represents the first example of catalytic asymmetric [1,2]-Stevens-type rearrangement based on alkynes but also constitutes the first asymmetric formal carbene insertion into the SiÀ O bond.

A facile fabrication of Fe and N codoped mesoporous carbon (MC), as an efficient heterogeneous catalyst for the highly selective reduction of nitroarenes, is described. The Fe and N co-doped MC nanosheets are easily synthesized via a hydrothermal reaction between citrate acid and magnesium citrate, followed by calcination in the presence of melamine and potassium ferrocyanide. The FeÀ N complex provides a unique active site for the selective reduction of 1-chloro-4-nitrobenzene, leading to the production of (E)-1,2-bis(4-chlorophenyl)diazene with a selectivity of > 96%, in < 40 mins. Control experiments based on nondoped, N-doped, and Fe-doped MC nanosheets demonstrate that selectivity greatly depends on the catalyst active component type, and that non-doped MC significantly contributes to the high efficiencies observed in the selective synthesis of azoxy compound intermediates. A broad range of substrates, including extra-functional groups on the nitroarenes rings, were successfully converted to the corresponding azo compounds at mild conditions with high selectivity.Aromatic azo compounds are widely used as raw materials in the chemical, food and pharmaceutical industries. [1][2][3][4][5] For example, azo compounds are considered as promising candidates across a wide range of applications as nonlinear optics, [6,7] photoregulation components, [8,9] catalytic promoters, [10] photochemical reaction species [11] and photo-mechanical switches. [12] Primary azo compounds are generally produced by azo coupling and the Mills reaction; [10,13] however, these COMMUNICATIONS Table 4. Mesoporous carbon (MC)-catalyzed reductive coupling of nitroarenes to yield the corresponding symmetric azoxy compounds.All reactions were performed in the presence of nitroarenes (1.0 mmol), NH 2 NH 2 · H 2 O (1.65 equiv.), KOH (1.5 equiv.) and MC (43 mg) in toluene.

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An efficient copper-catalyzed cyclization of N-propargyl ynamides with borane adducts through B–H bond insertion has been developed. A series of valuable organoboron compounds are constructed in generally good yields with a wide substrate scope and good functional group tolerance under mild reaction conditions. Importantly, this protocol via vinyl cation intermediates constitutes a novel way of B–H bond insertion.

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An efficient gold-catalyzed cascade cyclization of alkenyl diynes involving alkyne oxidation, carbene-alkyne metathesis and cyclopropanation has been developed, furnishing a series of tetracyclic γ-lactams bearing one quaternary carbon center and...

Transition-metal-catalyzed intramolecular carboalkoxylation of alkynes has attracted much attention in the past decades due to its high bond-forming efficiency and atom economy in the rapid assembly of functionalized cyclic compounds. However, compared with the well-established alkyne 1,2-carboalkoxylation, the related 1,1-carboalkoxylation has been far less exploited. Here, we report an unprecedented gold-catalyzed 1,1-carboalkoxylation of ynamides for the generation of exocyclic gold carbenes via exo-cyclization under room temperature. Subsequent 1,2-N-migration and 1,2-H-migration into the gold carbenes lead to the divergent and atom-economical synthesis of valuable tetrahydrofuran-fused 1,4-dihydroquinolines and furoindolines. Moreover, the asymmetric synthesis of these tricyclic N-heterocycles can be achieved by a chirality-transfer strategy, and the possibility of enantioselective cyclization via chiral gold-catalyzed kinetic resolution also emerges. In addition, the mechanistic rationale for this 1,1-carboalkoxylation, in particular accounting for the distinct migration into gold carbenes, is also strongly supported by theoretical calculations.