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The incorporation of oxygen atoms from air under aerobic conditions plays an important role in organic synthesis. Herein, Brønsted acids are found to be a two-in-one strategic catalyst to transform enamines from β-oxoamides and amines to pyrrolin-4-ones without an external photocatalyst under visible-light conditions. The Brønsted acid can inhibit the C-C bond fragmentation of the [2 + 2] adduct from enamine and 1 O 2 , but most importantly, it can form photosensitizers with enamine and pyrrolin-4-one product by acidochromism to promote the 1 O 2 generation.

Divergent synthetic methods for transforming isatins to 2-cyanoaryl carbamate and 2-cyanoaryl urea derivatives were developed using ammonium carbamate as the nitrogen source and iodobenzene diacetate as the oxidant. This reaction features mild conditions, broad substrate scope, and moreover, the use of toxic cyano-containing compounds is avoided.

Utilizing the easily available isatin-based propargyl amines prepared from isatins, terminal alkynes, and anilines, (2-(quinolin-2-yl)phenyl)carbamates were prepared by a one-pot reaction in sequence, combining the gold-catalyzed Friedel-Crafts cyclization, oxidative umpolung aza-Grob fragmentation, and nucleophilic addition. In this process, gold-catalyzed cyclization of isatin-based propargyl amines gave 1' H -spiro[indoline-3,2'-quinolin]-2-ones, which were oxidized in situ by hypervalent iodine via the aza-Grob fragmentation to afford isocyano intermediates 2-(2-isocyanatophenyl)quinolines. Followed by the nucleophilic addition with alcohol solvents, (2-(quinolin-2-yl)phenyl)carbamates were synthesized. This procedure features easy operation, a wide substrate scope, and mild conditions.

A formal [4 + 2] cycloaddition of N -tosylhydrazones with ortho -quinone methides was developed, affording the facile synthesis of diverse 1,3-oxazine derivatives under mild conditions. In this transformation, N -tosylhydrazones are used as a 1,2-dipole synthon under base-free conditions. Moreover, the substrate scope is broad, and the products are formed with high diastereoselectivities in most of the cases.

A challenging metal-free azide insertion of α-aryl α-diazoesters in the presence of B(C 6 F 5 ) 3 (5 mol %) was developed for the first time. The reaction features an easy operation, wide substrate scope, and mild conditions and affords the corresponding products in moderate to high yields. More importantly, alkene and alkyne functional groups were well tolerated because no cyclopropanation or cyclopropenation was observed. Furthermore, the corresponding azide products could be converted to primary amines or 1,2,3-triazole derivatives after simple transformations.

A efficient method to stereospecifically synthesize trans-substituted cyclopentene derivatives via the ring-opening rearrangement of readily available MCP alkenyl derivatives in moderate to good yields has been described. The control experiment based on the deuterium labeling experiment and the addition of TEMPO revealed that this transformation might proceed through a fast concerted pericyclic process rather than a simple radical pathway or an ionic pathway.

A convenient and efficient synthetic method for the construction of 2,3-disubstituted pyrrolamides in moderate to good yields is established. The in situ generated water significantly accelerates the reaction rate. A possible mechanism involving the cascade ring-opening and thermal-induced rearrangement to produce the five-membered ring is proposed.

A convenient and efficient method to synthesize 3-(2-chloroethyl)-5-aryl-4H-pyran-4-ones 2 and 2-chloro-3-(2-chloroethyl)-1-naphthaldehydes 3 in moderate to good yields was developed via the Vilsmeier-Haack reaction of readily available 1-cyclopropyl-2-arylethanones 1 at different temperature. This reaction proceeds via sequential enolization, ring opening, haloformylation, and intramolecular nucleophilic cyclization or Friedel-Crafts alkylation reactions to produce 2 or 3.

TMSOTf-mediated reactions of 2-aryl-1-(1-phenylcyclopropyl)ethanones 1 with allenic esters afford a novel method for the synthesis of 6-methyl-3a,7-diaryl-3,3a-dihydro-2H-benzofuran-4-one derivatives 2 in moderate yields. In addition, we also found that TMSOTf-mediated reactions of 1-cyclopropyl-2-arylethanones with ethyl acetoacetate can provide the corresponding 2,3-dihydrobenzofuran-4-ol and dihydrofuro[2,3-h]chromen-2-one in moderate yields via a sequential reaction involving a nucleophilic ring-opening reaction of the cyclopropane by H2O, one intermolecular aldol type reaction and two intramolecular aldol type reactions, a cyclic transesterification, dehydration, and aromatization. Moreover, by using methyl acrylate to replace allenic ester, the corresponding 7-aryl-3,5,6,7-tetrahydro-2H-benzofuran-4-one and 5-aryl-3,5,6,7-tetrahydro-2 H-benzofuran-4-one can be formed in moderate to high yields in the presence of Bi(OTf)2Cl. Plausible reaction mechanisms have also been provided on the basis of control experiments.