1.1. General Reactivity of Alkyne-Gold(I) Complexes
For centuries, gold had been considered a precious, purely decorative inert metal. It was not until 1986 that Ito and Hayashi described the first application of gold(I) in homogeneous catalysis.1 More than one decade later, the first examples of gold(I) activation of alkynes were reported by Teles2 and Tanaka,3 revealing the potential of gold(I) in organic synthesis. Now, gold(I) complexes are the most effective catalysts for the electrophilic activation of alkynes under homogeneous conditions, and a broad range of versatile synthetic tools have been developed for the construction of carbon–carbon or carbon–heteroatom bonds.

Gold(I) complexes selectively activate π-bonds of alkynes in complex molecular settings,4−10 which has been attributed to relativistic effects.11−13 In general, no other electrophilic late transition metal shows the breadth of synthetic applications of homogeneous gold(I) catalysts, although in occasions less Lewis acidic Pt(II) or Ag(I) complexes can be used as an alternative,9,10,14,15 particularly in the context of the activation of alkenes.16,17 Highly electrophilic Ga(III)18−22 and In(III)23,24 salts can also be used as catalysts, although often higher catalyst loadings are required.

In general, the nucleophilic Markovnikov attack to η2-[AuL]+-activated alkynes 1 forms trans-alkenyl-gold complexes 2 as intermediates (Scheme 1).4,5a,9,10,12,25−29 This activation mode also occurs in gold-catalyzed cycloisomerizations of 1,n-enynes and in hydroarylation reactions, in which the alkene or the arene act as the nucleophile.



Scheme 1

Anti-Nucleophilic Attack to η2-[AuL]+-Activated Alkynes

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Gold(I)-Catalyzed Activation of Alkynes for the Construction of Molecular Complexity

Kunbing Ouyang,†,‡ Wei Hao,† Wen-Xiong Zhang,*,†,§ and Zhenfeng Xi† †Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China ‡Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China

Transition-Metal-Catalyzed Cleavage of C-N Single Bonds.

Interest in homogeneous gold catalysis has undergone a marked increase. As strong yet air- and moisture-tolerant π-acids, cationic gold(I) complexes have been shown to catalyze diverse transformations of alkenes, alkynes and allenes, opening new opportunities for chemical synthesis. The development of efficient asymmetric variants is required in order to take full advantage of the preparative potential of these transformations. During the last few years, the chemical community has achieved tremendous success in the area. This review highlights the updated progress (2011–2015) in enantioselective gold catalysis. The discussion is classified according to the π-bonds activated by gold(I), in an order of alkynes, allenes and alkenes. Other gold activation modes, such as σ-Lewis acid catalyzed reactions and transformations of diazo compounds are also discussed.

Recent advances in enantioselective gold catalysis

Recent advances in the synthesis of biologically active spirooxindoles

Progress in the synthesis and transformations of alkylidenecyclopropanes and alkylidenecyclobutanes.

Rh-II-catalyzed intermolecular [3+2] cycloaddition of 2H-azirines with N-sulfonyl-1,2,3-triazoles is disclosed, in which a series of fully functionalized pyrroles is produced via rhodium azavinyl carbene intermediates. A distinct feature of this reaction is that the azavinyl carbene serves as a [2C] equivalent, instead of as [1C] or aza-[3C] synthons, which have been reported previously in cyclopropanations and [3+n] cycloadditions. Moreover, this methodology has also been successfully applied in the total synthesis of URB447 as well as the formal synthesis of Atorvastatin (Lipitor).

RhII‐Catalyzed [3+2] Cycloaddition of 2 H‐Azirines with N‐Sulfonyl‐1,2,3‐Triazoles

ticularly abundant in marine sponges. In bis(indole) alkaloids, two indole moieties are connected to various heterocyclic units. Compounds with this structural motif exhibit a wide spectrum of pharmacological activities, including antibacterial, antiviral, and cytotoxic activities, which make bis(indole) alkaloids and their analogues attractive targets for biomedical and synthetic studies. Gold catalysis, which is currently a hot topic in homogeneous catalysis, can be well understood with the concept of carbophilic p-acids, which are widely employed in the activation of alkynes, allenes, and alkenes. However, in contrast to gold-catalyzed enantioselective transformations involving allenes, there are relatively few examples involving alkynes. Echavarren and co-workers reported an elegant gold-catalyzed intramolecular reaction of indoles with alkynes, which proceeded through 6-endo-dig, 6-exo-dig, 7exo-dig, and 8-endo-dig cyclizations and were highly dependent on the oxidation state of the gold catalyst. Further investigations by this group indicated that similar spirocyclic intermediates were probably involved in cyclizations of various other substrates [Scheme 2, Eq. (1)]. Recently,

Gold-Catalyzed Intramolecular Regio- and Enantioselective Cycloisomerization of 1,1-Bis(indolyl)-5-alkynes

Yb(NTf2)3-catalyzed [3 + 3] cycloaddition between isatin ketonitrones and cyclopropanes is described. A variety of spiro[tetrahydro-1,2-oxazine]oxindoles were obtained in moderate to good yields along with good regioselectivities. This is the first example of the intermolecular [3 + 3] cycloaddition between ketone-derived nitrones and cyclopropanes.

Yb(NTf2)3-catalyzed [3 + 3] cycloaddition between isatin ketonitrones and cyclopropanes to construct novel spiro[tetrahydro-1,2-oxazine]oxindoles.

https://pubs.rsc.org/en/content/articlepdf/2015/cc/c5cc01313e

Amine-catalyzed tunable reactions of allenoates with dithioesters: formal [4+2] and [2+2] cycloadditions for the synthesis of 2,3-dihydro-1,4-oxathiines and enantioenriched thietanes

The first example for the preparation of enantioenriched azo compounds from hydrazones and Morita–Baylis–Hillman adducts has been developed, affording azo compounds incorporating an oxindole scaffold in up to 91% yield along with a 93% ee value under the catalysis of (DHQ)2AQN.

https://pubs.acs.org/doi/pdf/10.1021/jo5009977

(DHQ)2AQN-catalyzed asymmetric substitution of isatin-derived hydrazones with O-Boc-protected Morita-Baylis-Hillman adducts: A strategy for synthesizing enantioenriched azo compounds incorporating an oxindole scaffold.

Hai-Bin Yang

Papers

RhII‐Catalyzed [3+2] Cycloaddition of 2 H‐Azirines with N‐Sulfonyl‐1,2,3‐Triazoles

Gold-Catalyzed Intramolecular Regio- and Enantioselective Cycloisomerization of 1,1-Bis(indolyl)-5-alkynes

Yb(NTf2)3-catalyzed [3 + 3] cycloaddition between isatin ketonitrones and cyclopropanes to construct novel spiro[tetrahydro-1,2-oxazine]oxindoles.

Amine-catalyzed tunable reactions of allenoates with dithioesters: formal [4+2] and [2+2] cycloadditions for the synthesis of 2,3-dihydro-1,4-oxathiines and enantioenriched thietanes

(DHQ)2AQN-catalyzed asymmetric substitution of isatin-derived hydrazones with O-Boc-protected Morita-Baylis-Hillman adducts: A strategy for synthesizing enantioenriched azo compounds incorporating an oxindole scaffold.