Cationic Gold(<scp>I</scp>) Complexes: Highly Alkynophilic Catalysts for the <i>exo</i>‐ and <i>endo</i>‐Cyclization of Enynes

Nieto‐Oberhuber, Cristina; Muñoz, María Paz; Buñuel, Elena; Nevado, Cristina; Cárdenas, Diego J.; Echavarren, Antonio M.

doi:10.1002/anie.200353207

Cited by 586 publications

(285 citation statements)

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“…Alternatively, the cyclopropanation can be envisioned to occur step-wise via initial reaction of alkene with alkenyl cation 57 (Scheme 13), followed by nucleophilic interception of the resulting carbocation by alkenyl platinum. DFT calculations, which were carried out by Echavarren and co-workers, [11] suggested that in the case of Au(I) catalysis cyclopropanation proceeds directly via a single transition state located on the potential energy surface. In the absence of external nucleophile, highly electron deficient carbene 63 can undergo [1,2] alkyl shift to give zwitterion 64.…”

Section: Scheme 2 a C H T U N G T R E N N U N G (Pphmentioning

confidence: 99%

“…In 2004, as a part of their comprehensive study of gold-based catalysis of enyne cycloisomerizations, Echavarren and co-workers reported that cationic gold complexes were exceedingly effective in promoting alkoxycarbocyclizations of a wide range of 1,6-enynes. [11,28] A representative scope of this process, as well as the typical reaction conditions, is shown in Scheme 27.…”

Section: Formation Of Alkyl-and Alkenylmethylenecyclopentanes and Cycmentioning

confidence: 99%

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Gold and Platinum Catalysis of Enyne Cycloisomerization

2006

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This account provides a comprehensive overview of the development of gold and platinum catalysis of the enyne cycloisomerization. The use of these soft, alkynophilic metals enables mild, chemoselective and efficient transformations of a variety of readily available acyclic enynes to a wide range of synthetically useful carbocyclic and heterocyclic products. The review is organized according to diverse structural types of enynes that undergo skeletal cycloisomerizations. The account begins with an overview of transformations of primarily 1,6-enynesheptenes. This section is followed by the discussion of cycloisomerizations of 1,5-enynes, which enable a rapid access to a range of other cyclic products, including bicycloA C H T U N G T R E N N U N G [3.1.0]hexenes, cyclohexadienes, heterobicycloalkenes, methylenecyclopentenes, naphthalenes and methyleneindenes. In addition, the [3,3] rearrangement of 1,5-enynes provides efficient access to the corresponding allenes. The account concludes with an overview of the most recent studies on gold-and platinum-catalyzed cycloisomerizations of 1,4-and 1,3-enynes. Due to the rapidly increasing interest in this area during the past three to five years, we believe that this review provides a timely and comprehensive discussion of the development gold-and platinum-catalyzed cycloisomerization starting from the initial pioneering investigations to the latest advances in the field. A significant emphasis is placed on the mechanistic discussion of the observed manifolds of skeletal reorganizations.

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Section: Scheme 2 a C H T U N G T R E N N U N G (Pphmentioning

confidence: 99%

Section: Formation Of Alkyl-and Alkenylmethylenecyclopentanes and Cycmentioning

confidence: 99%

Gold and Platinum Catalysis of Enyne Cycloisomerization

2006

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“…Useful reactions for the formation of allylboronates are expected to be developed using this approach. 23 In summary, a borylative cyclisation leading to alkenylboronates has been developed. An appropriate choice of ligands allows formation of allylboronates.…”

Section: View Article Onlinementioning

confidence: 99%

Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications

et al. 2014

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The use of different ligands allows the preparation of either allyl-or alkenylboronates by Pd-catalyzed borylation of allylic carbonates containing alkyne groups. Unprecedented borylative cyclisation to alkenylboronates takes place with PCy 3 . The difficult dissociation of NHC ligands allows borylation of carbonates in the presence of alkynes. Oxidation, regioselective Suzuki coupling, as well as Au-catalyzed cycloisomerisation of boronates illustrate the potential synthetic applications of these reactions.Boronates are important synthetic reagents. They are stable and compatible with most functional groups and are environmentally friendly, tolerating oxygen and water. A wide variety of boronates can be used as nucleophilic partners in Suzuki cross-coupling reactions and allylboronates are reactive towards aldehydes and imines, just to cite the most common uses of these compounds. 1 For this reason, the development of methods for the preparation of boronates, avoiding the use of highly nucleophilic and basic reagents is of main interest. On the other hand, enynes constitute versatile starting materials for the formation of carbo and heterocycles, 2 skeletal rearrangements, 3 and alkoxy-cyclisation, 4 among other reactions. During the last few years, Pd-catalyzed borylative cyclisation reactions of polyunsaturated species have been developed by our group 5-9 and Bäckvall's group, 10 with the aim of preparing cyclized boronates. Our seminal work described an unprecedented preparation of homoallylic boronates starting with 1,6-enynes, in which esters substituting the allylic position were tolerated (Scheme 1, top). 5,11 In our previous studies, addition of ligands precluded the incorporation of the boron substituent. Now, we have found conditions in which the choice of the appropriate ligand allows control of the borylation of alkyne-containing allylcarbonates, affording simple Miyaura coupling to allylboronates, or unprecedented formation of alkenylboronates by borylative cyclisation, a method which is complementary to alkyne hydroboration and the usual reactions of strongly basic Li and Mg nucleophiles with B(OMe) 3 .Thus, we started our study by reacting enynes containing an allylic carbonate group (1). In our previous work mentioned above, 5 we reported that reactions of acetates or other ester derivatives, under ligandless conditions, took place without activation of the C-O bond, leading to homoallylic boronates containing the unreacted ester group (Scheme 1, top). Reactions in the presence of phosphines led to simple cycloisomerisation without incorporation of the boryl group.In contrast, reaction of carbonates 1a-l with B 2 (pin) 2 in the presence of Pd(OAc) 2 and the IMes ligand (formed in situ by deprotonation of the imidazolium chloride with t-BuOK) in xylene, afforded the corresponding allylboronates (Table 1). The reaction is fast (less than 30 min) and takes place under optimum conditions (50 1C) in the absence of added base, as usual for carbonates. A variety of starting compounds showing different ...

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“…Final desilylation by means of potassium fluoride delivered 5 possessing the desired terminal triple bond in 63% yield. We then examined the reactivity of 5 in the presence of catalytic amounts (4 mol%) of Echavarren's cationic gold(I) catalyst 28 in dichloromethane at room temperature, conditions that proved to be optimal in our previous study. We were delighted to observe the sole formation of furan derivative 6, which also readily occurred with only 2 mol% of the catalyst without hampering substrate conversion.…”

Section: Resultsmentioning

confidence: 99%