Carbometallation chemistry

• Ilan Marek

Beilstein J. Org. Chem. 2013, 9, 234–235, doi:10.3762/bjoc.9.27

• carbometallation reactions. In the past few decades, the intra- as well as intermolecular additions of various organometallic species to a large variety of alkynes, alkenes and allenes have been successfully reported. Although the carbometallation reaction on alkynes is generally a well-controlled and predictable

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• ) accounts for our experimental observations. Regardless of the exact structures of the silylation products 21, we did not observe any selectivity in this transformation. Quenching of 4 with N,N-dimethylformamide (DMF) and acetone Metalated allenes are known to be converted into allenic aldehydes on DMF

• metalated allenes has often been described in the chemical literature [17]. And the process is apparently successful for 2/4 also: the 1H NMR spectrum of the raw product, obtained in ca. 70% yield, shows the expected signals at δ 5.59 ppm (5J = 2.9 Hz) for the remaining allene proton and at 9.5 ppm (broad

• hydrocarbon 30. Oxidation of conjugated bisallenes The oxidation of allenes has already been studied previously. In seminal papers Crandall and his students described the epoxidation of differently substituted monoallenes and showed that methylene oxiranes are the initial oxidation products. These, however

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• organic synthesis for the first time. All classes of compounds containing at least two allene moieties are considered, starting from simple conjugated bisallenes and ending with allenes in which the two cumulenic units are connected by complex polycyclic ring systems, heteroatoms and/or heteroatom

• a recent phenomenon. During the 1970s (the very few) German chemists working on and with allenes used to answer inquiries about their research interests with the (German) sentence, “Ich arbeite (ueber) Allene”, with allene being Berlin dialect for “alone”, i.e., “I am working alone/on allenes”. The

• international scene was not very much different: allenes and cumulenes were regarded by the chemical community as exotic compounds, of interest at best for the study of stereochemical problems (going back to the days of van’t Hoff), but not as substrates and/or intermediates useful in preparative organic

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• hydroamination of the allenes 39, easily accessible by prototropic isomerization of the corresponding propargylamides (Scheme 20) [78]. The selective 5-exo-allylic hydroamination occurs in mild conditions in the presence solely of Pd(PPh3)4 under microwave irradiation by an initial coordination of the Pd(0

Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

• Zhi-Cong Geng,
• Jian Chen,
• Ning Li,
• Xiao-Fei Huang,
• Yong Zhang,
• Ya-Wen Zhang and
• Xing-Wang Wang

Beilstein J. Org. Chem. 2012, 8, 1710–1720, doi:10.3762/bjoc.8.195

• dipoles. Recently, the Ma group and Toste et al. have reported efficient methods for the synthesis of pyrazolidine derivatives by metal-catalyzed aminations of allenes [28][29][30][31][32]. Meanwhile, Lewis acid catalyzed carboamination reactions have also been reported as efficient methods for the

Chiral multifunctional thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of Morita–Baylis–Hillman carbonates with maleimides

• Hong-Ping Deng,
• De Wang,
• Yin Wei and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 1098–1104, doi:10.3762/bjoc.8.121

• : phosphines attack the middle carbon atom of allenes to produce the 1,3-dipolar synthon (Scheme 1, reaction 1), and phosphines add to the β-position of MBH carbonate to remove carbon dioxide and tert-butanol, affording the 1,3-dipolar synthon (Scheme 1, reaction 2). Concerning the asymmetric [3 + 2

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• of (3R)-3a (ellipsoids are drawn at a 50% probability level). Model proposed for the addition of lithiated allenes to nitrone 1a. Reactivity of N-glycosyl nitrones 1 towards dipolarophiles and nucleophiles leading to products of type A, B, C and D. Additions of lithiated alkoxyallenes to L-erythrose

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• , cobalt, nickel or palladium catalysts [4]. In recent years, however, platinum and particularly gold complexes have also emerged as excellent catalysts for the promotion of novel types of cycloaddition reactions, usually involving non-activated unsaturated systems (e.g., alkynes, allenes, alkenes or 1,3

• consequence this metal exhibits singular characteristics, such as a high carbophilicity, affinity for π-unsaturated systems (e.g., alkynes, alkenes or allenes), and a low propensity to participate in typical redox processes characteristic of other transition metal catalytic cycles (e.g., oxidative additions

• and reductive eliminations). Therefore, platinum(II) and particularly gold(I) or (III) complexes tend to activate alkynes, alkenes or allenes in a highly chemoselective manner; activation that opens interesting reaction pathways that usually involve carbocationic intermediates. Also very important is

Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

• Dawei Wang,
• Yanwei Zhang,
• Rong Cai and
• Xiaodong Shi

Beilstein J. Org. Chem. 2011, 7, 1014–1020, doi:10.3762/bjoc.7.115

• products were obtained in excellent yields (generally >90% yields with 1% loading). Besides the typical ester migrating groups, carbonates and carbamates were also found to be suitable for this transformation, which provided a highly efficient, practical method for the preparation of substituted allenes

• were produced after a long reaction time, 24–48 h; the crude NMR of the reaction mixtures did not show any allene products). This may be caused by the high reactivity of the corresponding aliphatic allenes under the reaction conditions (activated by TA–Au) and the overall better stability of the

• propargyl ester compared to the aliphatic substituted allenes (equilibrium favored the starting material). The reaction of cyclopropyl substituted propargyl ester 1j with the TA–Au catalyst gave a complex reaction mixture, which suggests possible ring opening and sequential cyclization as reported

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• : allenes; enantiopure pyridines; ketoenamides; multicomponent reactions; nonaflates; Introduction The pyridine core is ubiquitous in pharmacologically active agents, agrochemicals and natural products [1][2][3][4][5]. The HMG-CoA reductase inhibitors Glenvastatin and Cerivastatin are exemplarily mentioned

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• for the construction of N-heterocyclic compounds, metal-catalyzed intramolecular hydroamination of unactivated C–C multiple bonds is particularly straightforward and efficient [17][18]. Specifically, gold-catalyzed intramolecular hydroaminations of alkynes, alkenes and allenes show remarkable

Toward an integrated route to the vernonia allenes and related sesquiterpenoids

• Da Xu,
• Michael A. Drahl and
• Lawrence J. Williams

Beilstein J. Org. Chem. 2011, 7, 937–943, doi:10.3762/bjoc.7.104

• Da Xu Michael A. Drahl Lawrence J. Williams Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854, USA 10.3762/bjoc.7.104 Abstract The synthesis of a model endocyclic allene related to the vernonia allenes is described

• reported, perhaps in part due to the limited number of routes for cyclic allene construction that are sufficiently mild to effect allene formation in complex settings [9][10][11][12][13][14][15][16]. Our interest in the vernonia allenes was motivated in part by a desire to identify, and to simplify access

• pluripotent route that would enable direct access to a broad range of these targets would be useful and would offer advantages over single-target routes, especially in terms of overall step economy. Given the difficulties associated with the stereoselective preparation of endocyclic allenes, and the fact that

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• -alkylated amines in excellent yields (Scheme 21). Zeng and co-workers reported that cationic gold(I) complexes promote the addition of all types of non-tertiary amines 120 to a variety of allenes 121 to afford allylic amines 122 in good to excellent yields [58]. Importantly, the Markovnikov adduct was

• 90% yield. An efficient synthesis of multi-substituted N-aminopyrroles 135 via gold(I)-catalyzed cyclization of β-allenylhydrazones 134 was developed by Benedetti and co-workers (Scheme 24) [63]. This intramolecular cyclization method can be applied to both alkyl- or aryl-substituted allenes and

• 139 were obtained via gold(I)-catalyzed intramolecular dihydroamination of allenes with N,N′-disubstituted ureas 138. Iglesias et al. reported a complimentary diamination of alkenes 140 with homogeneous gold catalysts [66]. The key step is an intramolecular alkyl–nitrogen bond formation from a gold

Gold(I)-catalyzed formation of furans by a Claisen-type rearrangement of ynenyl allyl ethers

• Florin M. Istrate and
• Fabien Gagosz

Beilstein J. Org. Chem. 2011, 7, 878–885, doi:10.3762/bjoc.7.100

• suitable given the strong π Lewis acidic property of cationic gold species and their ability to activate alkynes and allenes towards the addition of oxygen functionalities [8][9][10][11][12][13][14][15][16]. The various alkynyl and allenyl compounds presented in Scheme 1 have thus proved to be suitable

Gold-catalyzed oxidation of arylallenes: Synthesis of quinoxalines and benzimidazoles

• Dong-Mei Cui,
• Dan-Wen Zhuang,
• Ying Chen and
• Chen Zhang

Beilstein J. Org. Chem. 2011, 7, 860–865, doi:10.3762/bjoc.7.98

• particular, water as a nucleophilic reagent has been used in the addition of alkynes and allenes [16][17][18]. In contrast, gold-catalyzed oxidation chemistry has been less well developed [25][26][27][28][29][30][31][32][33][34][35][36], although oxidative cleavage of carbon–carbon double bonds and carbon

• –carbon triple bonds by homogeneous gold catalysts was reported recently [28][29][33]. To the best of our knowledge, gold and other transition metal-catalyzed oxidations of allenes have not been reported [37][38]. In the context of ongoing studies on metal-catalyzed atom-economical reactions, we have been

• /hydration and oxidative cleavage of allenes to form α-diketones and aldehydes, and the synthesis of quinoxalines and benzimidazoles via the condensation of the resulting α-diketones and aldehydes with benzene-1,2-diamine [45][46][47][48][49][50][51][52][53][54][55][56]. Results and Discussion Our initial

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• matched by electrophilic activation modes, or ii) leads to different product frameworks on treatment with electrophiles. The focus is put on alkyne activation only, while related processes based on the activation of alkenes and allenes are not covered in this review. Review Heterocyclization The vast

Homoallylic amines by reductive inter- and intramolecular coupling of allenes and nitriles

• Peter Wipf and
• Marija D. Manojlovic

Beilstein J. Org. Chem. 2011, 7, 824–830, doi:10.3762/bjoc.7.94

• Peter Wipf Marija D. Manojlovic Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, PA 15260, USA 10.3762/bjoc.7.94 Abstract The one-pot hydrozirconation of allenes and nitriles followed by an in situ transmetalation of the allylzirconocene with dimethylzinc or zinc

• Schwartz’s reagent with allenes occurs at low temperature and provides a ready access to σ-bound allylzirconocenes [7]. These species can be added diastereoselectively to aldehydes and ketones to yield homoallylic alcohols, but they are generally not sufficiently reactive towards many other electrophiles [8

• reagent to allylzirconocenes, transient allylzinc intermediates can be successfully added to phosphoryl- and sulfonylimines to provide homoallylic amines in good yields and diastereoselectivities [15]. Of particular interest was the reaction of tin- or silicon-substituted allenes that furnish bis-metallic

A comparative study of the Au-catalyzed cyclization of hydroxy-substituted allylic alcohols and ethers

• Berenger Biannic,
• Thomas Ghebreghiorgis and
• Aaron Aponick

Beilstein J. Org. Chem. 2011, 7, 802–807, doi:10.3762/bjoc.7.91

• usually very poor leaving groups, but function extremely well in the present system, it seemed likely that a fairly robust group could perform satisfactorily here. Additionally, calculations suggest that in intermolecular hydroalkoxylation reactions of allenes the kinetic allylic ether products are

Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles

• Estela Álvarez,
• Delia Miguel,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez,
• Félix Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89

• nucleophilic nature of indoles [15], which are known to react with gold-activated alkynes or allenes [16][17], and by taking advantage of our reported methodology for the synthesis of 3-propargylindoles [18][19], we have shown that the indole nucleus is able to participate in gold-catalyzed 1,2-migration

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• feature: The ability of gold(I) and gold(III) species to activate unsaturated moieties due to the strong relativistic effects governing its coordination behavior [1][2][3][4][5][6]. However, beyond its Lewis acidity properties towards alkynes, allenes or alkenes, gold has also proved to be extremely

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• bonds [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Whereas alkynes, alkenes and allenes have been widely used as substrates or partners in gold-catalyzed reactions, it was only rather recently, in 2008, that cyclopropenes entered the field of gold catalysis despite their well-known high and

• %) was not as high as with Gagosz’s catalyst (83%). Lee and Hadfield took advantage of these findings to develop the regioselective addition of alcohols (used in excess) to allenes such as 14 catalyzed by [(IPr)AuOTf] (10 mol %) to produce the tert-allylic ethers 15 as the kinetic products (Scheme 8) [29

• (Equation 3, Scheme 32) [26]. Thus, alkynes appear to be chemoselectively activated in the presence of gold complexes in preference to cyclopropenes, whereas the latter moiety is more reactive than alkenes and possibly allenes, although in the latter case only a single example of competition was reported

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed. Keywords: alkynes; allenes; gold; heterocyclizations; β-lactams; Introduction The chemistry of alkynes and allenes has been extensively

• reactions of allenes are well-known in hydroxyallenes, the heterocyclization of alkoxyallenes is not an easy task and still remains a significant challenge. Gold-catalyzed heterocyclizations in alkynyl-β-lactams Aminocyclizations The precious metal-catalyzed formation of benzo-fused pyrrolizinones 19 from N

• latter, despite that fact that a priori this should be energetically more demanding. Conclusion In summary, regiocontrolled gold-catalyzed heterocyclization reactions of 2-azetidinone-tethered allenes and alkynes which lead to a variety of oxa- and azacycles have been developed. Density functional theory

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• of alkynes, allenes, and even alkenes, will continue to attract the attention of synthetic chemists. Lewis acid or Brønsted acid-catalyzed alkyne–carbonyl metathesis and a proposed [2 + 2] intermediate. Gold-catalyzed cyclization of internal alkynyl ketones. Proposed [2 + 2] mechanism for the

Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2011, 7, 601–605, doi:10.3762/bjoc.7.70

• cyclobutene; allene; allenyloxindole; chiral lanthanide shift reagent; chiral transfer; Introduction The [2 + 2] cycloaddition reaction of allenes and alkynes provides rapid entry into synthetically challenging alkylidene cyclobutene ring systems. We, along with others, have demonstrated the intramolecular

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• from terminal allenes in fair to good yields. The chemistry relies on a gold-catalyzed intermolecular oxidation of the 1,2-diene unit using 3,5-dichloropyridine N-oxide as the oxidant. The reaction tolerates a range of functional groups and shows excellent regioselectivity. Keywords: allene; catalysis

• ; gold; oxidation; regioselectivity; Introduction While alkynes are the most studied substrates in homogeneous gold catalysis [1][2][3][4][5][6][7][8][9], allenes [10] occupy a not-so-distant second place, and many versatile transformations have been developed either using allenes as substrates [11][12

• ][13][14][15][16][17] or via allenes generated in situ [18][19][20][21]. We have recently shown that highly reactive gold carbenes can be generated from alkynes via gold-promoted intermolecular oxidation by pyridine/quinoline N-oxides [22][23][24][25], making benign alkynes effective surrogates of