Palladium(II)-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions

• Tanveer Mahamadali Shaikh and
• Fung-E Hong

Beilstein J. Org. Chem. 2013, 9, 1578–1588, doi:10.3762/bjoc.9.180

• . Therefore, the development of an alternative general and mild procedure employing a stable and inexpensive ligand is still in great demand. Furthermore, the application of palladium complexes in the oxidative coupling of organo-boron compounds with olefins has attracted much attention in recent years [33

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• hemiester generated in situ from the substrate and phenylboronic acid. It is proposed that complexation of the tertiary nitrogen to boron and coordination of the carbonyl act in a push/pull fashion, simultaneously enhancing the nucleophilicity of the boronate oxygen as well as imposing a chiral environment

• the known allylic alcohol [58]. To synthesize ketone 57, we opted to utilize an asymmetric aldol reaction to set the stereochemistry of the β-hydroxy group. Since the report of Evans’s diastereoselective asymmetric aldol reaction using the boron enolates of N-acyloxazolidinones [59], numerous chiral

• boron enolate-based strategy using the N-acetylthiazolidinethione 58 (Scheme 14) for its high reported diastereoselectivity with aliphatic aldehydes and its avoidance of toxic tin reagents [61]. The reaction of the brightly colored 58 with but-3-enal proceeded in moderate yield, with an initial

α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

• Åsmund Kaupang and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2013, 9, 1407–1413, doi:10.3762/bjoc.9.157

• leaves the diazo function intact [4]. Among the reported transformations are substitutions of the diazomethyl hydrogen for electrophiles based on boron [5][6][7], nitrogen (NO2+) [8][9][10][11][12], silicon [13][14][15], phosphorous [16][17][18], sulfur [19][20][21] and halogens [10][22][23][24][25][26

Total synthesis of ochnaflavone

• Monica M. Ndoile and
• Fanie R. van Heerden

Beilstein J. Org. Chem. 2013, 9, 1346–1351, doi:10.3762/bjoc.9.152

• [31]. The synthesis of this compound has not been reported previously. The desired biflavone 7 was finally obtained in good yield by treating the dimeric chalcone with a catalytic amount of iodine in pyridine. Ochnaflavone (1) was obtained as a yellow solid by the reaction of 7 with boron tribromide

• solution of boron tribromide (206 mg, 0.82 mmol) in 5 mL dry CH2Cl2 was slowly added with a syringe to a stirred solution of 40 mg (0.07 mmol) 7 in 10 mL CH2Cl2 under nitrogen. After complete addition of BBr3, the reaction mixture was stirred at room temperature for 72 h, and then poured into 30 mL ice

• water. The mixture was then shaken to hydrolyse the excess BBr3 and boron complexes; a phenolic product was obtained by extraction with 3 × 20 mL EtOAc. The combined organic layers was dried over anhydrous magnesium sulfate and the solvent was removed in vacuo to obtain a dry crude reaction mixture

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• equilibrium in 1 due to a predominant OH∙∙∙F hydrogen bond or to other effects. A series of 2-X-phenylboranes (X = Cl, Br, NH2, PH2, OH and SH) were further computationally analyzed to search for electron donors to boron, capable of influencing the conformational equilibrium. Overall, the intramolecular OH

• ∙∙∙F hydrogen bond in 1 is quite stabilizing and dictates the 1hJF,H(O) coupling constant. Moreover, electron donation to the empty p orbital of boron (for noncoplanar BH2 moiety relative to the phenyl ring) is also significantly stabilizing for the NH2 and PH2 derivatives, but not enough to make the

• corresponding conformers appreciably populated, because of steric effects and the loss of πCC→pB resonance. Thus, the results found earlier for 2-fluorophenol about the lack of intramolecular hydrogen bonding are now corroborated. Keywords: conformational analysis; hydrogen bond; interactions with boron

Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

• Todd J. Eckroat,
• Abdelrahman S. Mayhoub and
• Sylvie Garneau-Tsodikova

Beilstein J. Org. Chem. 2013, 9, 1012–1044, doi:10.3762/bjoc.9.116

Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

• Holger F. Bettinger and
• Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

• thermal ring opening of 3 to 4 could be identified. These are the conventional disrotatory and conrotatory electrocyclic ring-opening pathways where the BN unit is only a bystander. Two more favourable paths are stepwise and involve 1,3-boron–carbon interactions. The lowest energy barrier for the

• -azaborine (4), a boron-nitrogen heterocycle that is isoelectronic and isosteric with benzene [15], results in its Dewar isomer 2-aza-3-borabicyclo[2.2.0]hex-5-ene (3) under the conditions of cryogenic noble gas matrix isolation [16]. Under these experimental conditions (T < 35 K), the isomerisation back to

• no longer just a bystander. The mode of rotation that results in MIN1 and MIN2 may be considered conrotatory, but the C4H group has moved significantly more than the C1H group. The electron pair of the breaking C1–C4 bond is utilized for interaction with the boron centre. As a consequence, the

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• for such reductions, boron reductants are widely used in the field of synthetic chemistry due to their availability and favorable reaction profiles [1][2][3]. For instance, sodium borohydride (NaBH4) is an inexpensive salt that is one of the most popular hydride sources for the reduction of aldehydes

• , but offered no clear advantages over acetic acid. No reduction occurs over 24 h when 1 and 2 are stirred in EtOAc without acid under these conditions. We next conducted a series of experiments to look at the boron products of such reactions by 11B NMR spectroscopy, and these results are summarized in

• of NHC-borane 1. Alcohol 3 is the reduction product, and the soluble boron products [25] were identified by 11B NMR spectroscopy of the crude product mixture. Each product spectrum gave the same four resonances, but in different ratios. With 1 equiv of 1 (entry 4), there was 55% of the starting NHC

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

• Ping-An Wang,
• Sheng-Yong Zhang and
• Henri B. Kagan

Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32

• , especially for one chiral nitrogen center and one chiral boron center. The configurations of the stereogenic centers in 5a are deduced from the configuration of the chiral auxiliary (S)-(−)-1-phenylethylamine to be S, 3S, 6R, 9S (chiral B atom) and 10R (chiral N atom), respectively. This novel tandem

Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach

• Florian Boeck,
• Max Blazejak,
• Markus R. Anneser and
• Lukas Hintermann

Beilstein J. Org. Chem. 2012, 8, 1630–1636, doi:10.3762/bjoc.8.186

• reaction requires high temperatures (140–250 °C, Scheme 1a) [16][19][20][21][22][23][24][25][26][27][28][29] or photochemical double-bond isomerization (Scheme 1b) [15][17][30][31]. An alternative boron tribromide induced lactonization proceeds at a lower temperature (Scheme 1c), but is not compatible with

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• cases in which M═E π bonding is inadequate to quench the electrophilicity of the multiply bonded group (particularly for heavier main-group elements, but also for carbon- and boron-based groups), affording a bonding situation that can be described as a Mδ−═Eδ+ FLP. Late metal silylenes, such as those

• by initial coordination of a heteroatom to the highly electrophilic boron center, followed by interaction with the metal to give a four-membered metallacycle and oxygen-atom transfer upon cycloreversion [61]. Thus, the reactions are initiated by the electrophilicity at B rather than the nucleophilic

Synthesis of new pyrrole–pyridine-based ligands using an in situ Suzuki coupling method

• Matthias Böttger,
• Björn Wiegmann,
• Steffen Schaumburg,
• Peter G. Jones,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2012, 8, 1037–1047, doi:10.3762/bjoc.8.116

• were not minimized. In principal the ester can react with the boronic acid, starting with the addition of the aqueous base (K2CO3). Yet, structure 21 is already activated for the coupling step, since a negative charge is located on the boron atom. In Scheme 6 the coupling reactions are shown; detailed

Toward unidirectional switches: 2-(2-Hydroxyphenyl)pyridine and 2-(2-methoxyphenyl)pyridine derivatives as pH-triggered pivots

• Christina Tepper and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2012, 8, 977–985, doi:10.3762/bjoc.8.110

• (6): 2-(2-methoxyphenyl)-3-methylpyridine (7) (36 mg, 0.18 mmol) was dissolved in dichloromethane (2 mL) and cooled to −70 °C. Then a 1 M boron tribromide solution in dichloromethane (0.6 mL, 0.60 mmol) was added. The mixture was warmed to room temperature overnight. Subsequently the solution was

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

• yield (75%) by using ion-exchange resin DOWEX-50 at 50 °C (Table 2, entry 4). As shown for compound 8, simultaneous cleavage was also possible, and the analytically pure compound 14 was isolated in comparable yield (Table 2, entry 3). Alternatively, demethylation of 12 by treatment with boron tribromide

• proof for the observed phenomenon was found in the 1H NMR spectrum (Supporting Information File 2) of 14 prior to purification, i.e., still containing BBr3, which acts here as a shift reagent. The influence of the coordinated boron species resulted not only in a strong low-field shift but it also

Aryl nitrile oxide cycloaddition reactions in the presence of pinacol boronic acid ester

• Sarah L. Harding,
• Sebastian M. Marcuccio and
• G. Paul Savage

Beilstein J. Org. Chem. 2012, 8, 606–612, doi:10.3762/bjoc.8.67

• favouring the oxidation of carbon–boron bonds, which makes boronic ester chemistry chemoselective, is a constraint that potentially limits the utility of nitrile oxide cycloadditions in the presence of a boronic acid ester. 4-Formylphenylboronic acid pinacol ester 4 is commercially available or easily

Asymmetric synthesis of quaternary aryl amino acid derivatives via a three-component aryne coupling reaction

• Elizabeth P. Jones,
• Peter Jones,
• Andrew J. P. White and
• Anthony G. M. Barrett

Beilstein J. Org. Chem. 2011, 7, 1570–1576, doi:10.3762/bjoc.7.185

• electrophile in the presence of boron trifluoride etherate (Table 1, entry 10) gave alcohol 6j. When (S)-propylene oxide was used instead there was no reaction, and indeed Schöllkopf noted significant levels of kinetic resolution when such reactions were performed with racemic oxiranes [23]. In our previous

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

• bond, followed by nucleophilic attack on the iminium generated in situ. The resulting vinylpalladium species reacts with the boron or alkynyl compound as previously shown. Allenylamines are also compatible with this anti-Wacker process, leading to more substituted tetrahydropyridines 16 in good to

Functionalization of heterocyclic compounds using polyfunctional magnesium and zinc reagents

• Paul Knochel,
• Matthias A. Schade,
• Sebastian Bernhardt,
• Georg Manolikakes,
• Albrecht Metzger,
• Fabian M. Piller,
• Christoph J. Rohbogner and
• Marc Mosrin

Beilstein J. Org. Chem. 2011, 7, 1261–1277, doi:10.3762/bjoc.7.147

• -coupling As aryl- and heteroarylmagnesium reagents are readily available, it would be highly desirable if cross-couplings could be directly realized using these organometallics without the need of further transmetalation to zinc, boron or other metals. However, the disadvantage of this cross-coupling

Nano copper oxide catalyzed synthesis of symmetrical diaryl sulfides under ligand free conditions

• K. Harsha Vardhan Reddy,
• V. Prakash Reddy,
• A. Ashwan Kumar,
• G. Kranthi and
• Y.V.D. Nageswar

Beilstein J. Org. Chem. 2011, 7, 886–891, doi:10.3762/bjoc.7.101

• [10][11], Alzheimer’s and Parkinson’s diseases [12]. During the last decades, transition and boron group metals, such as palladium [13][14][15][16][17][18], nickel [19][20], copper [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], iron [38], indium [39][40], lanthanum [41] and

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• , separation of the diastereomers by flash chromatography was possible, affording the pure tetrahydropyridine derivative trans-133 in 74% yield. Successive epoxidations on enantiopure trans-133 and then 134, followed each time by regioselective epoxide opening (with a selenium–boron complex and water

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

• Sebastian Schlecht,
• Walter Frank and
• Manfred Braun

Beilstein J. Org. Chem. 2011, 7, 615–621, doi:10.3762/bjoc.7.72

• 10.3762/bjoc.7.72 Abstract Racemic boronate–imine and boronate–amine complexes 8 and 10, both featuring a stereogenic boron atom were synthesized from 2-amino-1,1-diphenylethanol (5) and characterized by crystal structure analyses. Proof of enantiomerism at the boron center for the novel boronate–amine

• complex 10 was established by separation of the enantiomers. Racemization barriers were found to be in the same range for both amine and imine complexes (100–110 kJ/mol). Keywords: boron; chirality; coordination chemistry; crystal structure; stereochemistry; Introduction Enantiomerism of main group

• hetero elements has been investigated thoroughly for compounds with stereogenic sulfur [1], phosphorus [2], nitrogen [3] and silicon atoms [4]. By comparison, stereogenic tetrahedral-coordinated boron has been studied to a much lesser extent. This is partly because it was incorporated in a chiral

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

• '-binaphthyls with two additional substituents at the 3 and 4 positions, could also be expected to be high. AB patterns were observed for the methylene hydrogens on the five-membered ring of 20b and on the carbon bearing the methoxy group of 20c. Treatment of 20b with boron tribromide converted the methoxy

• )acetylene, boron tribromide, and (1S)-(−)-camphanoyl chloride were purchased from chemical suppliers and were used as received. 1-Iodo-2-[2-(trimethylsilyl)ethynyl]benzene was prepared by treatment of 1-bromo-2-[2-(trimethylsilyl)ethynyl]benzene in THF with n-butyllithium at −78 °C followed by treatment

The preparation of 3-substituted-1,5-dibromopentanes as precursors to heteracyclohexanes

• Bryan Ringstrand,
• Martin Oltmanns,
• Jeffrey A. Batt,
• Aleksandra Jankowiak,
• Richard P. Denicola and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2011, 7, 386–393, doi:10.3762/bjoc.7.49

• the development of polar, zwitterionic nematic liquid crystals having large longitudinal dipole moments for formulation of nematic materials with positive dielectric anisotropy [24][25]. The zwitterions consist of six-membered sulfonium rings attached to a boron cluster, either [closo-1-CB9H10]− or

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• the different electronic configurations of boron and carbon. The CnHn systems are assembled from CH units each of which supplies three atomic orbitals and three electrons to the cage. Each carbon can link to three others via conventional two-electron bonds, thus forming electron-precise molecules. In

• the borane that has a capping boron linked to six others. We are unaware of any attempted syntheses of this molecule but, as depicted in Scheme 14, suitable disconnections reveal that a C3-bridged ansa-[5]peristylane is an enticing precursor to 15. Highly symmetric inorganic polyhedranes The major

First synthesis of 2-(benzofuran-2-yl)-6,7-methylene dioxyquinoline-3-carboxylic acid derivatives

• Wentao Gao,
• Jia Liu,
• Yun Jiang and
• Yang Li

Beilstein J. Org. Chem. 2011, 7, 210–217, doi:10.3762/bjoc.7.28

• reactions of 2-hydroxybenzophenones with Corey–Chaykovsky reagent [36], cyclization of 2-acyloxy-1-bromomethylarenes with Cr(II)Cl2/BF3·OEt2 catalyst [37], and boron tribromide-promoted tandem deprotection–cyclization of 2-methoxyphenylacetones [38], 2-methoxyphenylmethanols [39] and 2-hydroxy-3