Ambient gold-catalyzed O-vinylation of cyclic 1,3-diketone: A vinyl ether synthesis

• Yumeng Xi,
• Boliang Dong and
• Xiaodong Shi

Beilstein J. Org. Chem. 2013, 9, 2537–2543, doi:10.3762/bjoc.9.288

• ether; Introduction The past decade has witnessed the fast growth of homogeneous gold catalysis as one of the important branches in transition-metal chemistry [1][2][3][4][5][6][7][8][9]. The utility of cationic gold(I) complexes as π-carbophilic acids toward alkyne and allene activation renders them

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• processes. Keywords: alkyne; allene; asymmetric catalysis; cycloaddition; enantioselective; gold; gold catalysis; Introduction In the past decade, there have been extraordinary advances in the development of novel stereoselective gold(I)-catalyzed transformations [1][2][3][4][5][6][7][8][9][10]. In this

• , we will present cycloaddition processes (i) with a gold–carbene intermediate, (ii) involving an allene activation to generate a gold–allyl cationic intermediate and, (iii) in which the proposed key reactant is a vinylgold zwitterionic species. Review Cycloadditions involving gold–carbene

• enantioselectivity. Cycloadditions initiated by activation of allenes Gold(I) catalysts can efficiently activate allenes in a highly chemoselective way, triggering the formation of allenyl cationic species. Different structures have been proposed to represent these gold-activated allene complexes, including η2

An approach towards azafuranomycin analogs by gold-catalyzed cycloisomerization of allenes: synthesis of (αS,2R)-(2,5-dihydro-1H-pyrrol-2-yl)glycine

• Jörg Erdsack and
• Norbert Krause

Beilstein J. Org. Chem. 2013, 9, 1936–1942, doi:10.3762/bjoc.9.229

• allene synthesis by copper-mediated SN2’-substitution [51] (Table 1, see below). In order to establish suitable reaction conditions, we first examined the synthesis of the butyl-substituted model substrate 6a. Treatment of propargyl tosylate 5a with the organocopper reagent formed in situ from n-BuMgCl

• , CuBr·SMe2, and LiBr [52] afforded allene 6a with up to 74% yield (Table 1, entries 1–3). In order to achieve complete conversion, a large excess of the nucleophile is required. The yield could be raised further by using the cyanocuprate n-BuCu(CN)MgBr [53][54][55] or the heterocuprate n-BuCu(SPh)Li [56

• 5b as starting material, allene 6a was obtained in 85% yield using n-BuCu(CN)MgBr·2LiCl as nucleophile (Table 1, entry 6). In contrast, use of the heterocuprate n-BuCu(SPh)Li led to decomposition (Table 1, entry 7). Propargyl phosphate 5c is also a suitable precursor of allene 6a (Table 1, entries 8

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• product 4e in 52% yield according to initial E-configured 1e. The structure of compound 4e was determined by 1H NMR NOE spectra. The reaction was still operable with 1f, bearing a 1,2-disubsituted allene, giving the desired 4f in moderate yield (49%). Its E-configuration was determined by NOE measurements

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• phosphine oxides OC-64 and OC-69 for the enantioselective desymmetrization of meso-stilbene oxide to provide the corresponding vicinal chlorohydrin 96 in up to 82% ee. More recently, Ready [86] and co-workers have synthesized a series of chiral phosphine oxides (OC-70 to OC-77) based on an allene backbone

• oxides. The variation of the substituents on the allene itself was tolerated in the desymmetrization processes, but both the yields and the enantioselectivities are sensitive to changes in the aryl rings on the phosphine oxide. It was found that the diphenyl-substituted catalyst OC-73 is a highly

• meso-epoxides. Some chiral phosphoramide and chiral phosphine oxides. The proposed mechanism of the chiral HMPA-catalyzed desymmetrization of meso-epoxides. The Chiral phosphine oxides (OC-70 to OC-77) based on an allene backbone. Chiral pyridine N-oxides used in enantioselective desymmetrization of

Homolytic substitution at phosphorus for C–P bond formation in organic synthesis

• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 1269–1277, doi:10.3762/bjoc.9.143

• thiophosphination (Scheme 9). Detailed mechanistic studies revealed that comproportionation between PhSe–SePh and Ph2P–PPh2 occurs smoothly to generate PhSe–PPh2 as the actual reactive species. Selenophosphination of terminal allene affords (2-phenylselenyl-2-alkenyl)diphenylphosphine regioselectively (Scheme 11

Gold-catalyzed intermolecular hydroamination of allenes with sulfonamides

• Chen Zhang,
• Shao-Qiao Zhang,
• Hua-Jun Cai and
• Dong-Mei Cui

Beilstein J. Org. Chem. 2013, 9, 1045–1050, doi:10.3762/bjoc.9.117

• the intermolecular hydroamination of allenes with sulfonamides is shown. The reaction proceeded smoothly under mild conditions for differently substituted allenes giving N-allylic sulfonamides in good yields with high regioselectivity and E-selectivity. Keywords: allene; gold catalysis

• -donating or an electron-withdrawing group gave good isolated yields of the corresponding adducts (Table 3, entries 1 and 2). Whereas hydroamination of the monosubstituted heteroaromatic allene 1d also lead to the conversion into the expected addition product 3j, hydroamination of the monoalkyl-substituted

• aliphatic allene 1e formed a 71:29 mixture of linear product (3ka) and branch product (3kb) under the same conditions (Table 3, entry 4). Furthermore, disubstituted allenes also worked well. Differentially 1,1-disubstituted allene 1f reacted with sulfonamide to afford trans-adducts 3l with high selectivity

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

• Benito Alcaide,
• Pedro Almendros,
• M. Teresa Quirós and
• Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

• ][37][38][39][40][41]. The Boc protective group has been widely used in allene chemistry, being an inert and recommended partner in gold- and palladium-catalyzed aminocyclizations of allenes [42]. On the other hand, reports of gold-catalyzed cyclizations leading to heterocycles that contain more than

• one heteroatom are rare [43][44][45][46][47][48]. Besides, it has been reported very recently that the Au(I)-catalyzed cyclization of a N-phenethyl-N-Boc-protected allenamide failed [49]. Despite the above precedents, but in continuation of our interest in heterocyclic and allene chemistry [50][51][52

• 3,4-dihydro-2H-1,3-oxazin-2-ones 4 (arising from 6-exo-dig cyclization) were achieved, with the nucleophilic oxygen attacking the central allene carbon atom in each case. This is an interesting result, because the available examples on related metal-catalyzed allene heterocyclizations usually lead to

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• –Fuchs reaction followed by quenching of the acetylide with cyclohexanone furnishes propargyl silane 136, a compound that is cleanly transformed into allene 137 upon exposure to tetrabutylammonium fluoride [54]. This approach represents perhaps the most versatile route to functional propargyl silanes

• . Synthesis of bicyclic cyclobutane motifs. Construction of the CD rings of steroids. Rapid assembly of polyquinanes. Formation of a polycyclic structure via an allene intermediate. A polycyclic structure via the alkylative Birch reduction. Synthesis of polycyclic pyrimidines and indoline structures

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

• with 5J = 2.8 Hz for the remaining allenic proton in the 1H NMR spectrum and by two singlets at δ 202.5 and 202.8 ppm for the central allene carbon atoms in the 13C NMR spectrum. When the methylation is carried out after 3 equiv of n-butyllithium have been added, small amounts of a dimethyl product

• propargyl structure. The “half-rearranged” diol 24 is a slightly yellow oil at room temperature. Structure-defining are the missing allene proton and three signals for carbon atoms not connected to a hydrogen atom: the central allene carbon atom at 210.0 ppm and the two acetylene carbon atoms at δ 72.0 and

• 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

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

• bisallene with unsubstituted allene carbon atoms [9]. And finally, also in the 1960s, Jacobs and Prempree reported on the synthesis of the first hexa-alkylated bisallene, hydrocarbon 5 [10][11]. We shall return to the preparation of these three compounds later. The upsurge in interest in allene chemistry is

• 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

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

• ) catalyst to the indole nitrogen giving the Pd(II)-hydride complex XIV. Such an intermediate would be susceptible to insertion of the allene group into the Pd–H bond to generate the π-allyl-Pd(II) complex XV, which in turn would undergo the intramolecular formation of the new carbon–nitrogen bond, which

Synthesis and in silico screening of a library of β-carboline-containing compounds

• Kay M. Brummond,
• John R. Goodell,
• Matthew G. LaPorte,
• Lirong Wang and
• Xiang-Qun Xie

Beilstein J. Org. Chem. 2012, 8, 1048–1058, doi:10.3762/bjoc.8.117

• as particularly efficient for maximizing structural diversity [3]. Previous work in the Brummond laboratory has demonstrated that an allene-containing β-carboline provided a good starting point for synthesizing six novel types of hetero-frameworks, all skeletally unique [4]. Moreover, scope and

• the mixtures could not be readily separated by column chromatography, diastereomeric ratios were determined by 1H NMR and were advanced without further purification. Reaction of allene 6 under the silver-nitrate-mediated cyclization conditions afforded the desired fused pyrrolines 1. However, in the

• -phosponium hexafluorophosphate (PyBroP), provided the requisite allene-yne substrates 9{1,2}–9{1,8}. For the coupling reaction of the ynoic acids with an aryl group on the terminus of the alkyne 8{5–8}, the desired allene-ynes 9{1,5}–9{1,8} were afforded along with the [2 + 2] cycloadducts 2{1,5}–2{1,8

Synthesis of axially chiral oxazoline–carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe₂

• Feijun Wang,
• Shengke Li,
• Mingliang Qu,
• Mei-Xin Zhao,
• Lian-Jun Liu and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 726–731, doi:10.3762/bjoc.8.81

• chiral NHC–Au(I) complexes (4–6) with a binaphthyl or biphenyl framework [13][14]. These Au(I) complexes were applied to catalyze the asymmetric cyclization of 1,6-enynes or allene in up to 70% ee, and the asymmetric intramolecular hydroamination of allene in up to 44% ee. We previously reported a novel

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

• quenched with water. Then, warming to room temperature was followed by extraction with Et2O (3 × 25 mL), and the combined organic layers were stirred overnight with the drying agent (MgSO4). When cyclisation of the primarily formed allene adducts was complete (TLC monitoring, hexane/ethyl acetate 4:1, p

Synthesis of fluoranthenes by hydroarylation of alkynes catalyzed by gold(I) or gallium trichloride

• Sergio Pascual,
• Christophe Bour,
• Paula de Mendoza and
• Antonio M. Echavarren

Beilstein J. Org. Chem. 2011, 7, 1520–1525, doi:10.3762/bjoc.7.178

• (Table 2, entries 11 and 12). The reaction of 3a with Pd(OAc)2 as catalyst proceeded differently to give known (E)-9-(3-phenylallylidene)-9H-fluorene (9) [60], presumably via the formation of the corresponding allene as an intermediate (Scheme 2). Substrates 7b–j, prepared by alkylation of fluorenyl

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• partners through a Pd-mediated allylic amination The allene carbopalladation process with organic halides is known to generate a π-allylpalladium intermediate, which can be trapped by intermolecular carbo- or heteronucleophiles to produce the corresponding three-component adduct. This strategy was used by

• Ma and coworkers for the selective preparation of five-membered nitrogen heterocycles starting from allene-bearing nucleophilic centers [41]. In this context, the same authors developed a new synthesis of substituted imidazolidinones 75 through a palladium-catalyzed, three-component reaction of 2,3

• -allenylamines, organic halides and isocyanates [42]. In this process, there is first a carbopalladation of the functionalized allene with the aryl iodide, followed by reaction of the internal aza-nucleophile with the highly electrophilic isocyanate derivative, before premature trapping of the initially formed π

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

• . In this review we will summarize some of the most remarkable examples, and present the mechanistic rational underlying the transformations. Keywords: alkene; alkyne; allene; catalysis; cycloaddition; gold; Introduction In modern organic synthesis, the criteria of efficiency, versatility, economy

• cases, the gold activation of the alkyne promotes a 1,3-acyloxy shift that leads to ketone allenic intermediates of type VI (Scheme 3) [42][43]. Then, an intramolecular attack of the carbonyl group on the activated allene generates a benzopyrilium intermediate (VII) which undergoes a concerted and

• related cycloaddition reactions. Indeed, the group of Toste described in 2007 a (2 + 2) intramolecular cycloaddition reaction between allenes and alkenes by gold catalysis [87]. The proposed mechanism is based on an activation of the allene to give a cationic metal species which undergoes a cyclization to

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

• , which allowed the effective activation of the alkyne without affecting the reactivity of the allene ester intermediates. These results led to the investigation of the preparation of allene ester intermediates with TA–Au catalysts under anhydrous conditions. As expected, the desired 3,3-rearrangement

• . Keywords: allene; chemoselectivity; gold catalysis; ligand effect; organometallic; Introduction The past decade has seen rapid growth in the use of homogeneous gold catalysis for conducting powerful organic transformations [1][2][3][4][5][6][7][8][9]. Like many other transition metal complexes, the

• one of the most important reaction modes in the Au(I) promoted transformation [21][22][23][24][25][26][27][28][29][30][31]. Recent experimental and computational mechanistic studies revealed the 3,3-rearrangement to form the allene ester intermediate [32][33] as the key step in this transformation

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

• present sequence are also discussed. Keywords: C–C fragmentation; endocyclic allene; natural product; total synthesis; Introduction Well over 150 allene-containing natural products are known [1][2][3][4][5]. Among these, intriguing complex structures were assigned by Bohlmann and co-workers to isolates

• from the aerial parts of Vernonia species collected mainly from northern Brazil about 30 years ago (1–3, Figure 1) [6][7][8]. These bicyclic germacranolides are the only known endocyclic allene-containing natural products. Interestingly, no synthetic studies of these complex natural products have been

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

• rearrangement followed by nucleophilic attack of the Boc-protected nitrogen atom. A similar method to synthesize the 2-vinylpiperidin-3-ol 158 by a highly stereoselective gold-catalyzed allene cyclization has been reported (Scheme 27) [72]. The ring expansion of cyclopropane derivatives provides a powerful

• catalytic amount of phosphite–gold(I) pre-catalyst and a silver additive. Notably, the addition is regioselective for the allene terminus, and generates (E)-allylation products 202. The direct C–H functionalization of indoles or pyrroles is an efficient method for the introduction of vinyl and aryl groups

• 222, while the stereochemistry of the reaction depends on the ring size. In some gold(I)-catalyzed cycloaddition reactions, regiochemistry of the product is controlled by the ligand [100][101]. For example, the triphenylphosphinegold(I)-catalyzed reaction of allene–diene 224 provided a 2:1 mixture of

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

• new strategies that involve a metal-mediated cyclization of an allene or an alkyne derivative with an oxygen functionality have appeared in the literature [7]. Among the transition metals that are commonly employed in these transformations (viz. Cu, Ag, Pd and Au), gold has proven to be particularly

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

• to form α-diketones and aldehydes in good yields is presented. Further directed synthesis of quinoxalines and benzimidazoles, via the condensation of the resulting α-diketones and aldehydes with benzene-1,2-diamine, was achieved in high yields. Keywords: allene; benzimidazole; gold-catalysis

• -withdrawing fluoro or bromo substituent on the benzene ring also took place smoothly (Table 2, entries 5 and 6). Disubstituted allenes were also examined. Thus, the 1,3-disubstituted allene 1g, was oxidized to afford α-diketone 2g and aldehyde 3c in 35% and 32% yields, respectively (Table 2, entry 7

• of quinoxalines and benzimidazoles via the condensation of the resulting α-diketones and aldehydes with benzene-1,2-diamine was achieved in high yields. This reaction appears to proceed via oxidation/hydration and oxidative cleavage of the allene, and investigations into the mechanism of this

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

• chloride provides functionalized homoallylic amines. An intramolecular version of this process leads to 3-aminotetrahydrofurans and 3-aminotetrahydropyrans. Keywords: allene; 3-aminotetrahydrofurans; 3- and 4-aminotetrahydropyrans; hydrozirconation; nitrile; transmetalation; Introduction The reversible

• to that of the zinca-Claisen reaction observed by Suzuki and co-workers [38]. Analogous to the previous work in our group [15], the silyl-substituted allene 16 produced the (E)-vinylsilane 17 as the sole product in this reaction. Given the success of the one-pot intermolecular reductive coupling of

• to depend on the allene substitution. The intramolecular variant of this reaction was used to prepare 3-aminotetrahydrofurans and 3-aminotetrahydropyrans, and these addition products can subsequently be transformed into synthetically valuable β-amino acid building blocks. Coupling constant analysis

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

• architectures; for recent reviews on Au-catalysis, see [2][3][4][5][6][7][8][9][10]. Generally, only mild conditions are necessary and these processes are highly chemoselective. While the typical substrates employed in these reactions effect transformations on alkyne, allene, and alkene moieties, recent reports