A novel gold(I)-catalyzed intramolecular tandem cyclization reaction of ortho-(arylethynyl)arenemethylenecyclopropanes provided an efficient approach to prepare functionalized 11H-benzo[a]fluorene derivatives in moderate to good yields. Further transformations as well as applications of the products have been presented and a plausible reaction mechanism has also been proposed on the basis of deuterium labeling and control experiments.

The [4+3] annulation reaction of crotonate-derived sulfur ylides with thioaurones has, for the first time, been reported using NaH as the base. A diverse array of 2,5-dihydrobenzo[4,5]thieno[3,2-b]oxepines is obtained in good to excellent yields. The proposed mechanism is investigated and supported by DFT calculations.

Alkynones can be activated by phosphine as a nucleophilic catalyst, and then trapped by a series of trifluoroacetyl phenylamides to afford cycloaddition products. Through subtly adjusting the substituent of trifluoroacetyl phenylamides, the addition of water and changing the reaction temperature, two kinds of highly regioselective cycloaddition products were obtained in moderate to excellent yields. Plausible mechanisms were proposed and supported by the deuterium-labeling experiments and DFT calculations. DFT calculations demonstrate that the currently accepted intramolecular proton transfer processes involved in these reactions are impossible, and these proton transfer processes can proceed with the assistance of substrates containing an acidic moiety or by the addition of water. Our mechanistic studies provide reasonable explanations for the regioselectivity affected by the protic additive H2O, and the reaction temperature.

The mechanisms for dirhodium-catalyzed ring expansion reactions of azide tethered methylenecyclopropanes and their analogues were systematically investigated by DFT calculations. The calculation results indicate that the dirhodium catalyst is essential for generating a reactive Rh2–nitrene intermediate having radical character; however, it is not essential for controlling final product selectivities. For substrates involving a three-membered ring, the experimentally obtained C–N bond formation product is a thermodynamically favored product. In contrast, for substrates having a larger ring, the kinetically favored product is the main product. The DFT calculations presented here account for previous experimental findings, and throw light on other dirhodium-catalyzed reactions involving nitrene or carbene intermediates.

Lu's [3 + 2] cycloaddition reaction has experienced explosive development due to its versatile and powerful ability to access highly functionalized carbo- and heterocycles. After the first example reported by Prof. Xiyan Lu's group, many research groups expanded its substrate scope, and developed its asymmetric variants, and demonstrated its synthetic applications as well. This review briefly introduces the history of Lu's [3 + 2] cycloaddition reaction and highlights the important developments and synthetic applications with respect to Lu's [3 + 2] cycloaddition reaction.

AbstractN2-Selective autocatalytic ditriazolylation reactions of cyclopropenones and tropone with N1-sulfonyl-1,2,3-triazoles are reported for the first time. In contrast to previous methods for preparing N2-substituted bis(1,2,3-triazolyl) compounds, the present reaction achieved ditriazolylation in one step under simple and user-friendly conditions with a wide substrate scope. A plausible mechanism has been proposed relying on preliminary mechanistic investigations.

AbstractA new zwitterion generated from different electron-deficient alkenes and phosphines has been designed and its reactivity was explored. We demonstrated that this new zwitterion directed a novel [2+1+2] cycloaddition reaction between vinylpyridines and isatin-derived electron-deficient alkenes, affording spirocyclopenteneoxindole derivatives containing three stereocenters in moderate to good yields with good diastereoselectivities. A plausible mechanism has been proposed relying on preliminary mechanistic investigations and supported by theoretical calculations.

A gold(I)-catalyzed cycloisomerization of easily available 1,5-enynes containing a cyclopropane ring has been developed, efficiently providing cyclobutane-fused 1,4-cyclohexadiene, tricyclic cyclobutene, biscyclopropane and 1,3-cyclohexadiene derivatives in moderate to excellent yields. When the phenyl group was not ortho substituted, 1,4-cyclohexadienes could be produced. With an ortho substituent, three different products could be selectively synthesized by control of the temperature and the used gold(I) catalyst. The 1,5-enyne substrate first undergoes a classical enyne cycloisomerization to form a tricyclic cyclobutene key intermediate, which undergoes subsequent transformation to produce the desired products. A plausible reaction mechanism was proposed according to deuterium labeling experiments and intermediate trapping experiments, as well as DFT calculations. In our current reaction, the ortho substituent on the phenyl group controls the reaction outcome and the ortho substituent effect was found to originate from steric and electronic factors.

The reactions of cyclopropenones with nucleophiles (H2O or methanol) could be catalyzed by nitrogen-containing Lewis bases or phosphorus-containing Lewis bases, affording the corresponding mono- or multi-substituted allenic esters in moderate to excellent yields.

The reactions of cyclopropenones with nucleophiles (H2O or methanol) could be catalyzed by nitrogen-containing Lewis bases or phosphorus-containing Lewis bases, affording the corresponding mono- or multi-substituted allenic esters in moderate to excellent yields.

A gold(I)-catalyzed cycloisomerization of easily available 1,5-enynes containing a cyclopropane ring has been developed, efficiently providing cyclobutane-fused 1,4-cyclohexadiene, tricyclic cyclobutene, biscyclopropane and 1,3-cyclohexadiene derivatives in moderate to excellent yields. When the phenyl group was not ortho substituted, 1,4-cyclohexadienes could be produced. With an ortho substituent, three different products could be selectively synthesized by control of the temperature and the used gold(I) catalyst. The 1,5-enyne substrate first undergoes a classical enyne cycloisomerization to form a tricyclic cyclobutene key intermediate, which undergoes subsequent transformation to produce the desired products. A plausible reaction mechanism was proposed according to deuterium labeling experiments and intermediate trapping experiments, as well as DFT calculations. In our current reaction, the ortho substituent on the phenyl group controls the reaction outcome and the ortho substituent effect was found to originate from steric and electronic factors.

The mechanisms for dirhodium-catalyzed ring expansion reactions of azide tethered methylenecyclopropanes and their analogues were systematically investigated by DFT calculations. The calculation results indicate that the dirhodium catalyst is essential for generating a reactive Rh2–nitrene intermediate having radical character; however, it is not essential for controlling final product selectivities. For substrates involving a three-membered ring, the experimentally obtained C–N bond formation product is a thermodynamically favored product. In contrast, for substrates having a larger ring, the kinetically favored product is the main product. The DFT calculations presented here account for previous experimental findings, and throw light on other dirhodium-catalyzed reactions involving nitrene or carbene intermediates.