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

• ; oxidation; quinoxaline; Introduction Recently, several research groups have developed gold-catalyzed homogeneous catalytic reactions [1]. A variety of organic transformations have been shown to be mediated by gold(I) or gold(III) complexes in solution. In addition to its ability to activate unsaturated C–C

• interested in the use of gold for simple and highly efficient transformations. Additionally, quinoxaline and benzimidazole skeletons are common building blocks for the preparation of substances with pronounced biological activities [39][40][41][42][43][44]. Herein, we report the gold(I)-catalyzed oxidation

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

• analogous manner either by using gold-catalysts or electrophilic iodine sources. Typically, these processes are easily understood by postulating stabilized cationic intermediates. For example, aromatic 1,5-enynes can be cyclized to the corresponding naphthalenes in the presence of gold(I) catalysts as

• migration of R3 are strictly limited to compounds that bear a quaternary center (R3 = alkyl, R2 ≠ H). As shown for the gold(I)-catalyzed reaction of 1,5-enyne 53, the formation of the bicyclo[3.1.0]hexene 54 is driven by the release of ring strain. Enynes with R3 = H undergo exclusively a hydride shift to

Au(I)/Au(III)-catalyzed Sonogashira-type reactions of functionalized terminal alkynes with arylboronic acids under mild conditions

• Deyun Qian and
• Junliang Zhang

Beilstein J. Org. Chem. 2011, 7, 808–812, doi:10.3762/bjoc.7.92

• electronic structure as Pd(0) and can easily interact with the acetylenic group, and has the ability to undergo the Au(I)/Au(III) redox cycles [24][25]. In addition, with an increasing interest in the chemistry of gold(I) and gold(III) compounds, more and more studies have provided strong evidence for the

• efficiency was quite low (Table 1, entries 4, 5). Without Selectfluor® as additive, the cross-coupling reaction did not occur (Table 1, entry 6), indicating that it was crucial for this transformation via oxidation of gold(I) to the gold(III) species [26][27][28][29][30][31][32]. Reducing the amount of

• cationic gold(I) species A is oxidized by Selectfluor® to give a gold(III) species B [26][27][28][29][30][31][32][36]. With the aid of base, the reaction between B and alkyne affords intermediate C. The weak Au–F bond and the strong B–F bond drive the trans-metalation to produce intermediate D [29][36][37

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

• -biphenyl)di-tert-butylphosphine]gold(I) hexafluoroantimonate, the cyclization reactions were complete within minutes to hours, depending on the substrate. The reaction progress was monitored by GC, and comparisons between substrates demonstrate that reactions of allylic alcohols are faster than the

High chemoselectivity in the phenol synthesis

• Matthias Rudolph,
• Melissa Q. McCreery,
• Wolfgang Frey and
• A. Stephen K. Hashmi

Beilstein J. Org. Chem. 2011, 7, 794–801, doi:10.3762/bjoc.7.90

• gold(I) catalyst to [Mes3PAu]NTf2 [41], only 10 was again observed. Thus, neither of the two oxidation states of the gold catalyst gave any product derived from the intercepted intermediate (the solvent was changed to CDCl3 since the activity of gold(I) is significantly reduced by MeCN). Intramolecular

• dinuclear gold(I) complex 36 [44] gave the same result (Figure 3). When the catalyst was changed to platinum(II) chloride in acetone, a complex mixture of inseparable products was obtained. Since the two diastereoisomers 28a and 28b with the propargylic stereocenters were separable, we investigated the gold

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

• N-heterocyclic carbene ligands [30] also produced 3a as the major compound of the corresponding mixtures (Table 1, entries 5 and 6). It was decided to increase the π-acceptor character of the ligand [31], and, in this case, the employment of a triphenylphosphite–gold(I) complex led to a slight

• influence of the metal counter ion was then studied. Thus, several silver salts were employed for the generation of the cationic catalytic active gold(I) complex, and it was concluded that the effect on the selectivity is almost negligible (Table 1, entries 9–12). Nevertheless, it should be noted that no

• , temperature), in the gold(I)-catalyzed tandem reactions of 3-propargylindoles initiated by 1,2-indole migrations. We have been able to switch the preference of 3-propargylindoles, bearing (hetero)aromatic substituents at both propargylic and terminal positions of the alkyne moiety, from undergoing an aura-iso

Highly efficient gold(I)-catalyzed Overman rearrangement in water

• Dong Xing and
• Dan Yang

Beilstein J. Org. Chem. 2011, 7, 781–785, doi:10.3762/bjoc.7.88

• Dong Xing Dan Yang Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China 10.3762/bjoc.7.88 Abstract A highly efficient gold(I)-catalyzed Overman rearrangement of allylic trichloroacetimidates to allylic trichloroacetamides in water is reported. With this

• environmentally benign and scalable protocol, a series of C3-alkyl substituted allylic trichloroacetamides were synthesized in good to high yields. Keywords: allylic trichloroacetamides; allylic trichloroacetimidate; gold(I) chloride; Overman rearrangement; water; Introduction The aza-Claisen rearrangement of

• moderate yields were achieved [25][26][27][28]. Very recently, our group developed an efficient gold(I)-catalyzed decarboxylative aza-Claisen rearrangement of allylic N-tosylcarbamates for the synthesis of N-tosyl allylic amines [29]. This reaction was performed in water and therefore represented an

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

• the various approaches to access these ubiquitous scaffolds, the gold(I)-catalyzed ring expansion of cyclopropanols and cyclobutanols is considered one of the most powerful and versatile methods. In 2005, Toste and co-workers reported the treatment of 1-(phenylethynyl)cyclopropanol (11) with tris(4

• -trifluoromethylphenyl)phosphine gold(I) to give alkylidenecyclobutanone 12 quantitatively (Scheme 3, reaction 1) [19]. In an analogous manner, alkynylcyclobutanols were suitable substrates for gold(I)-catalyzed ring expansions only when a terminal alkyne group was present (Scheme 3, reaction 2). Thus, cyclobutanol 13

A racemic formal total synthesis of clavukerin A using gold(I)-catalyzed cycloisomerization of 3-methoxy-1,6-enynes as the key strategy

• Jae Youp Cheong and
• Young Ho Rhee

Beilstein J. Org. Chem. 2011, 7, 740–743, doi:10.3762/bjoc.7.84

• followed by several other racemic and enantioselective syntheses [2][3][4][5][6][7][8][9][10][11][12][13][14]. Herein, we report a short formal total synthesis of racemic clavukerin A employing the gold(I)-catalyzed cycloisomerization of a 3-methoxy-1,6-enyne as the key strategy, which was recently

• cyclization (path B). The cycloheptenone 4 could then be synthesized from the enyne substrate 5 by gold(I)-catalyzed cycloisomerization. The synthesis of enyne substrate 5 commenced with the alkylation of methyl acetoacetate with the known bromide 6 [24] to provide compound 7 in 55% yield (Scheme 2

• proceeds via the initial heterocyclization intermediate 10 and the subsequently rearranged intermediate 11 (Scheme 3). Notably, when the gold(I)-catalyzed reaction was carried out on a multi-mmol scale, there was no decrease in the yield at the same catalyst loading. With ketone 4 in hand, the final stage

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

• cyclopropene 1. Though a large excess of styrene (100 equiv) was used, triene 45 resulting from the self-coupling of 1 still predominated, and the cyclopropanation product 46 was isolated in low yield (19%) as a single trans diastereomer (Scheme 21) [23]. In their investigations on the bonding model for gold(I

• impact of cationic versus carbene-like species on the reactivity in olefin cyclopropanation [17]. In the presence of an olefin and a cationic gold(I) catalyst, cyclopropenone acetal 3 did not provide any cyclopropanation product, which is in agreement with the fact that the organogold species generated

• cation would be preferentially formed upon coordination of a gold complex. However, this implies that substituents have to be present at C3 in order to handle stable substrates. Thus, allyl 3,3-dimethylcyclopropenylcarbinyl ether 59 was prepared and several gold(I) and gold(III) species {AuCl3, AuBr3

Sequential Au(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

• Lei Zhou,
• Yizhou Liu,
• Yan Zhang and
• Jianbo Wang

Beilstein J. Org. Chem. 2011, 7, 631–637, doi:10.3762/bjoc.7.74

• Lei Zhou Yizhou Liu Yan Zhang Jianbo Wang Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China 10.3762/bjoc.7.74 Abstract The gold(I

• )-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in good yields. The reaction follows a catalytic sequence of gold carbene formation/water O–H insertion/alcohol-alkyne cyclization. The gold(I) complex is the only catalyst in each of these

• Dias and co-workers with a gold(I) ethylene complex [7]. Although the scope of those studies was limited to ethyl diazoacetate, the examples therein demonstrated that gold complexes can be used as efficient catalysts in carbene transfer reactions with diazo compounds. On the other hand, the development

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

• cephalosporolides. Gold(I) chloride in methanol induced the cycloisomerization of a protected alkyne triol with concomitant deprotection to give a strategically hydroxylated 5,5-spiroketal, despite the potential for regiochemical complications and elimination to furan. Other late transition metal Lewis acids were

• conditions that ultimately resulted in the acquisition of our target structures [28]. Gold(I) chloride emerged as the best choice for the desired transformation. The key precedents for the desired cycloisomerization are shown in Scheme 3, although many methods are available [30][31][32][33][34] and no

• (Table 1, entry 1) resulted in decomposition of the substrate, but at room temperature the spiroketal was obtained in modest yield (Table 1, entry 2). Reactions involving Ziese’s dimer were disappointing (Table 1, entry 3), but gold(I) chloride in methylene chloride (cf. Scheme 3, Reaction 3) gave more

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• . A gold(I)-catalyzed hydroarylation of indoles with styrenes as well as with aliphatic and cyclic alkenes was developed by Che et al. [64]. [AuCl(PPh3)]/AgOTf was the catalyst system of choice and the reaction was, depending on the substrate, performed under thermal or microwave-assisted conditions