Synthesis of trifunctional cyclo-β-tripeptide templates

• Frank Stein,
• Tahir Mehmood,
• Tilman Plass,
• Javid H. Zaidi and
• Ulf Diederichsen

Beilstein J. Org. Chem. 2012, 8, 1576–1583, doi:10.3762/bjoc.8.180

• . Residual solvent proton signals were used as an internal standard. Synthesis of compounds (S)-tert-Butyl(7-azido-1-diazo-2-oxoheptan-3-yl)carbamate. (S)-6-Azido-2-(tert-butoxycarbonylamino)hexanoic acid (7.38 g, 27.1 mmol, 1.00 equiv) was dissolved in dry THF (108 mL) under an argon atmosphere. The

• purification. DC (EtOAc/n-pentane 2:3 + 1% AcOH): Rf = 0.73. (S)-7-Azido-3-(tert-butoxycarbonylamino)heptanoic acid (3). A solution of silver trifluoroacetate (219 mg, 990 µmol, 0.110 equiv) in triethylamine (3.79 mL, 27.0 mmol, 3.00 equiv) was slowly added to a solution of (S)-tert-butyl 7-azido-1-diazo-2

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• migration of the N-acyl glycine derivatives [18]. The other consists of C–N bond-forming reactions, such as (c) a rhodium-catalyzed N–H insertion reaction with α-diazo-β-keto esters [19][20][21], and (d) α-oxidation of β-keto esters to the corresponding oximes and the subsequent hydrogenation [22]. However

Impact of cyclodextrins on the behavior of amphiphilic ligands in aqueous organometallic catalysis

• Hervé Bricout,
• Estelle Léonard,
• Christophe Len,
• David Landy,
• Frédéric Hapiot and
• Eric Monflier

Beilstein J. Org. Chem. 2012, 8, 1479–1484, doi:10.3762/bjoc.8.167

• , respectively) indicative of the deleterious role played by the diazo function on the inclusion phenomenon. In fact, two distinct parameters could be implicated to explain the low Kass values observed for 1 and 2. First, the hydrophilic diazo function had less affinity for the hydrophobic CD cavity than the

• biphenyl moiety. Additionally, the phosphane nonlinear geometry resulting from the zig-zag diazo structure also disfavored the recognition process between the phosphane and the CD cavity. The existence of phosphaneCD supramolecular complexes was confirmed by using a 2D NMR T-ROESY sequence sensitive to

• concentration range was narrow for aggregates constituted by diazo phosphanes 1 or 2 and rather broad for aggregates constituted by 3 or 4. Second, above a stoichiometric RAME-β-CD/phosphane ratio, the RAME-β-CD impact on aggregates became deleterious to the point that the aggregates were destroyed. Most of the

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• -position are significantly more effective than aryl substituents in stabilizing the pyridinium ions formed through acetyl cation addition. Photo-switchable 3,4-diaminopyridines including a diazo moiety are potentially useful as special-purpose catalysts. The azobenzene substituent itself is electron

• -withdrawing in nature and the calculation of ACA values can thus be used to optimize the design of these Lewis bases (Table 15). In terms of their overall architecture the pyridine bases presented in Table 15 fall into two different categories: The first of these attaches the diazo bridge to the C8-position

• of the pyridoquinoxaline framework and leads to a significant drop in ACA values (e.g., in compounds 411/412). In the second category, the diazo bridge connects to the 3,4-diaminopyridine amino nitrogen atoms through a phenyl spacer unit and leads to significantly larger ACA values as is best seen

Photochemistry with laser radiation in condensed phase using miniaturized photoreactors

• Elke Bremus-Köbberling,
• Arnold Gillner,
• Frank Avemaria,
• Céline Réthoré and
• Stefan Bräse

Beilstein J. Org. Chem. 2012, 8, 1213–1218, doi:10.3762/bjoc.8.135

• source, in a clean way, avoiding almost completely the formation of the undesired diazo derivatives 3. The side reaction is supposedly reduced due to a lesser effect of heating owing to the small bandwidth irradiation and minimized exposure time through the miniaturized flow setup. During these tests, it

High-affinity multivalent wheat germ agglutinin ligands by one-pot click reaction

• Henning S. G. Beckmann,
• Heiko M. Möller and
• Valentin Wittmann

Beilstein J. Org. Chem. 2012, 8, 819–826, doi:10.3762/bjoc.8.91

• conveniently prepared by employing a one-pot procedure for Cu(II)-catalyzed diazo transfer and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) starting from commercially available amines. These glycoclusters were probed for their binding potencies to the plant lectin wheat germ agglutinin (WGA) from

• ligands. In this report, we describe the preparation of such a series of multivalent WGA ligands by a one-pot procedure for diazo transfer and azide–alkyne cycloaddition [48] starting from commercially available di- and triamines and the propargyl glycoside of N,N’-diacetylchitobiose. Binding potencies

• scaffolds [52][53][54]. Recently, we reported a convenient one-pot procedure for diazo transfer and azide–alkyne cycloaddition [48] giving access to multivalent triazole-linked structures starting from amines. For the synthesis of triazole-linked glycoclusters, commercially available amines A1–A6 (Figure 1

Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

• Marc Enßle,
• Stefan Buck,
• Roland Werz and
• Gerhard Maas

Beilstein J. Org. Chem. 2012, 8, 433–440, doi:10.3762/bjoc.8.49

• Marc Enssle Stefan Buck Roland Werz Gerhard Maas Institute of Organic Chemistry I, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany 10.3762/bjoc.8.49 Abstract Methionine, S-benzylcysteine and S-allylcysteine were converted into 2-diazo-3-oxo-4-phthalimidocarboxylic esters 8a–c in

• reaction. Keywords: α-aminoacids; carbonyl ylides; cycloaddition; α-diazo-β-ketoesters; sulfonium ylides; Introduction The synthetic potential of diazo compounds, in particular of α-diazoketones and α-diazoesters, is greatly widened by the ability of the derived carbene or metal-carbene intermediates to

• epoxidation, aziridination and olefination reactions [12][13] are common reaction channels. The intramolecular formation of sulfonium ylides from α-diazocarbonyl compounds tethered with alkylthio or arylthio groups has been studied by the research groups of Davies [14], Moody [15], and West [16]. From α-diazo

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• expansion of 12, via 2H-azirine 3, affords didehydroazepine 4, which can be trapped by variety of nucleophiles to provide the corresponding azepine 5. Alternatively, intersystem crossing (ISC) of 12 gives rise to 32, which can dimerize to form diazo compound 6. Performing the reaction in the presence of

• pure 9a in 45% yield. Only traces of the diazo product were observed in the NMR spectrum of the crude mixture. A variety of other 3H-azepinones was prepared in moderate to good yields under the optimized reaction conditions (Scheme 4, Table 2). Residual starting material was easily recovered by silica

Continuous gas/liquid–liquid/liquid flow synthesis of 4-fluoropyrazole derivatives by selective direct fluorination

• Jessica R. Breen,
• Graham Sandford,
• Dmitrii S. Yufit,
• Judith A. K. Howard,
• Jonathan Fray and
• Bhairavi Patel

Beilstein J. Org. Chem. 2011, 7, 1048–1054, doi:10.3762/bjoc.7.120

• . Pyrazoles are also useful intermediates for many industrial products and it is, therefore, not surprising that many synthetic methods have been developed for the preparation of such heterocyclic systems, for example, through 1,3-dipolar cyclo-additions of diazo compounds and the direct condensation of 1,3

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

• gold-catalyzed synthesis of dihydrofuran-3-ones 63, in which terminal alkynes 62 were used as equivalents of α-diazo ketones to generate α-oxo gold carbenes (Scheme 12) [37]. The α-oxo gold carbenes were produced via gold-catalyzed intermolecular oxidation of 62. This provides improved synthetic

• flexibility in comparison with the intramolecular strategy and offers a safe and economical alternative to those based on diazo substrates. A catalytic approach to functionalized divinyl ketones through a gold-catalyzed rearrangement of (3-acyloxyprop-1-ynyl)oxiranes 64 has also been developed [38]. The

Gold-catalyzed naphthalene functionalization

• Pedro J. Pérez,
• M. Mar Díaz-Requejo and
• Iván Rivilla

Beilstein J. Org. Chem. 2011, 7, 653–657, doi:10.3762/bjoc.7.77

• photochemical route for the functionalization of benzene using diazo compounds to provide a carbene moiety. The first step of this transformation consists of the addition of such a unit to the aromatic double bond to give a norcaradiene intermediate that spontaneously undergoes ring opening to afford the more

• stable cycloheptatriene product (Scheme 1) [2]. Nearly one century later, Teyssié and co-workers discovered the potential of dirhodium tetraacetate and related Rh2(L-L)4 compounds as catalysts for the decomposition of diazo compounds and subsequent transfer of the carbene moiety to several saturated and

• cyclopropanation, ring opening and the formal insertion of CHCO2Et into the aromatic C–H bonds were observed, with 2a being by far the major product (Scheme 2). In the course of our research, focussed on the development of group 11 metal-based catalysts for carbene transfer reactions from diazo compounds [10], we

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

• steps. Keywords: alkyne; carbene O–H insertion; cyclization; diazo compounds; gold catalysis; 1H-isochromene; Introduction Transition metal carbene complexes are versatile intermediates and can undergo diverse transformations, including X–H (X = C, O, S, N, etc.) insertions, cyclopropanations, ylide

• formation, and 1,2-migrations [1][2][3][4][5]. Among the various methods to generate metal carbene complexes, transition metal-catalyzed decomposition of diazo compounds is the most straightforward and is highly reliable. Various transition metals have been found to decompose diazo compounds and then

• transfer a carbene unit to saturated or unsaturated organic substrates [3]. However, compared to the other group 11 metals, i.e., copper and silver, there are only a few reports on gold-catalyzed carbene transfer reactions of diazo compounds [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In 2005

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

• toxic and potentially explosive α-diazo ketones (Scheme 1A). Synthetically useful structures such as oxetan-3-ones [22], dihydrofuran-3-ones [23], azetidin-3-ones [24] and α,β-unsaturated ketones [25] are readily accessed via these gold carbene intermediates. This led us to consider whether or not

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• indeed involved was carried out by Reedich and Sheridan [29]: By incorporating a diazo group into the last formed bond of the cyclopropyl ring in the meta photocycloadduct [30], they would be able to see whether the biradical formed by the extrusion of nitrogen gave the same products as the meta

• photocycloaddition (Scheme 6). This was indeed the case, as very similar ratios of the two distinct stereoisomers C and D were found to be formed from the diazo compounds A and B as well as from the photocycloaddition of o-xylene to cyclopentadiene. This finding seems to indicate that a biradical structure is indeed

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes

• Yu-Hsuan Wang,
• Joshua F. Bailey,
• Jeffrey L. Petersen and
• Kung K. Wang

Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58

• with iodine [7]. 1-Ethynyl-2-iodo-benzene (15) [30] was prepared in quantitative yield by desilylation of 1-iodo-2-[2-(trimethylsilyl)ethynyl]benzene with sodium hydroxide in methanol. 1-Ethynyl-2-(methoxymethyl)benzene (4b) [31] and dimethyl (1-diazo-2-oxopropyl)phosphonate [32] were prepared

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• precursors for the “second generation” catalysts bearing NHC ligands are the alkylidene ruthenium complexes coordinated with two phosphines [1]. For recent reviews see [2][3][4]. There are several routes for accessing five-coordinated ruthenium(II) alkylidene complexes such as diazo-transfer [5] and the

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• alkylidene moiety originates from 2,2-diphenylcyclopropene, was soon replaced by the second version B [9], since the benzylidene ligand is more conveniently available from phenyldiazomethane. The obvious disadvantages of handling non-stabilized diazo compounds stimulated investigations into the use of

Synthesis of glycosylated β³-homo-threonine conjugates for mucin-like glycopeptide antigen analogues

• Florian Karch and
• Anja Hoffmann-Röder

Beilstein J. Org. Chem. 2010, 6, No. 47, doi:10.3762/bjoc.6.47

• by Norgren et al. [29]. TN antigen derivative Fmoc-Thr(αAc3GalNAc)-OH (1a) was prepared according to published procedures [32][33] and converted into the corresponding diazo ketone upon treatment with isobutyl chloroformate in the presence of N-methylmorpholine (NMM) and diazomethane (Scheme 1

• united organic phases were dried over KOH at −25 °C for 3 h. General procedure (GP1) for the synthesis of diazo ketones: The free acid (1 equiv) was dissolved in 2 mL of dry THF under an argon atmosphere. At −25 °C, 1 equiv of NMM and 1 equiv of isobutyl chloro formate were added subsequently and the

• . The organic layer was dried over Na2SO4, filtered, and the solvents were removed under reduced pressure. The resulting diazo ketones were used without further purification. General procedure (GP2) for the Wolff-rearrangement: The diazo ketone (1 equiv) was dissolved in a mixture of THF/H2O (9:1) and

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• in 46% overall yield. Interestingly, oxidation with hydrogen peroxide gave predominantly the N-allylic system rather than the vinylic one. This is in accordance with the precedent established by the laboratory of K.B. Sharpless [80][81]. The overall yield from diazo-ester 67 was only 2% and was

One-pot preparation of substituted pyrroles from α-diazocarbonyl compounds

• Fernando de C. da Silva,
• Mauricio G. Fonseca,
• Renata de S. Rianelli,
• Anna C. Cunha,
• Maria C. B. V. de Souza and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2008, 4, No. 45, doi:10.3762/bjoc.4.45

• purification of crude residues by column chromatography led to the pyrroles 7a–n in moderate to good yields. Their structures were confirmed mainly based on their 13C and 1H NMR spectral data which are depicted in the experimental section. Since the reactivities of the diazo compounds are different there were

Transition- metal/Lewis acid free synthesis of acyl benzothiophenes via C-C bond forming reaction

• Sarbani Pal,
• Mohammad Ashrafuddin Khan,
• P. Bindu and
• P. K. Dubey

Beilstein J. Org. Chem. 2007, 3, No. 35, doi:10.1186/1860-5397-3-35

• an expensive transition metal catalyst along with toxic carbon monoxide gas[13] or unstable diazo compounds,[18] or pyrophoric BuLi,[19][20] or a multistep synthesis of starting material.[14] The simplest and straightforward method for the synthesis of acyl benzothiophenes appeared to be the Friedel

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• electrocyclic ring closures to furans.[9][17][18] Related ring closures of o-acyl phenylcarbenes to isobenzofurans have been reported (Scheme 9).[19][20][21] These carbenes were formed as transient intermediates by photolytic or chemical cleavage of diazo or diazirine compounds. Isobenzofurans formed in this