Highly chemo-, enantio-, and diastereoselective [4 + 2] cycloaddition of 5H-thiazol-4-ones with N-itaconimides

• Shuai Qiu,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2016, 12, 2293–2297, doi:10.3762/bjoc.12.222

• decreases the free energy of the second formal Mannich reaction, thus improving the reaction rate and chemoselectivity of the [4 + 2] cycloaddition. To extend the usefulness of this reaction, we demonstrate that the adduct can be efficiently reduced with borane. As shown in Scheme 2, 3a was readily reduced

DNA functionalization by dynamic chemistry

• Zeynep Kanlidere,
• Oleg Jochim,
• Marta Cal and
• Ulf Diederichsen

Beilstein J. Org. Chem. 2016, 12, 2136–2144, doi:10.3762/bjoc.12.203

• potassium bromide substitution under overall retention of configuration due to double inversion. Next, the subsequent reduction of carboxylic acid 6 to alcohol 7 was achieved by borane dimethyl sulfide (BMS) under dry conditions. The reaction between alcohol 7 and 3-mercaptopropanenitrile (8) resulted in

Practical synthetic strategies towards lipophilic 6-iodotetrahydroquinolines and -dihydroquinolines

• David R. Chisholm,
• Garr-Layy Zhou,
• Ehmke Pohl,
• Roy Valentine and
• Andrew Whiting

Beilstein J. Org. Chem. 2016, 12, 1851–1862, doi:10.3762/bjoc.12.174

• substituent, each with a different means of cyclisation. A versatile and stable quinolin-2-one intermediate was identified, which could be reduced to the corresponding THQ with borane reagents, or to the DHQ with diisobutylaluminium hydride via a novel elimination that is more favourable at higher

• larger scales was slightly lower, though the DHQ was still isolated in a satisfactory 66% yield on one gram scale. Unlike borane, LiAlH4 and similar reagents, DIBAL did not cause de-iodination, even with larger excesses (up to 2 equivalents). There are few references to this type of reaction in the

A T-shape diphosphinoborane palladium(0) complex

• Patrick Steinhoff and
• Michael E. Tauchert

Beilstein J. Org. Chem. 2016, 12, 1573–1576, doi:10.3762/bjoc.12.152

• (CyDPBPh)Pd(0) 9, which was characterized by X-ray analysis. Keywords: ambiphilic ligand; coordination chemistry; diphosphinoborane; organometallics; palladium; Introduction The amplification of traditional bidentate chelating L2-type ligands with a tethered borane functionality (e.g., Bourissou’s

• diphospinoborane (o-PR2-C6H4)2BR’ ligand RDPBR’) has received considerable attention [1][2][3], with first catalytic applications emerging [4]. The acyclic boron group in these ligands can adopt a variety of coordination modes (Figure 1) [5]. The borane can act as a σ-acceptor ligand in case of η1-B coordination

• chelating diphosphine, such as in Hofmanns Rucaphos complexes 6, are very scarce [11]. While the dative Pd→B bond is strong in zerovalent Pd(0) DPB complexes such as 2, only weak Pd→B interactions have been observed for the respective Pd(II) complexes [7][12]. Discrimination by the borane functionality

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• iodide 97. The following palladium-catalyzed B-alkyl Suzuki–Miyaura cross coupling between the borane derived from alkene 98 and vinyl iodide 97 furnished a Z-configured alkene. Deprotection of the trimethylsilyl ether then afforded alcohol 99. A rhodium(II)-catalyzed O–H insertion reaction of the

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

• Gabriele Grieco,
• Olivier Blacque and
• Heinz Berke

Beilstein J. Org. Chem. 2015, 11, 1656–1666, doi:10.3762/bjoc.11.182

• can be tuned and, based on these properties, they possess great electronic flexibility. These ligands or catalysts reached a prominent position in the mentioned fields of chemistry. It is noteworthy that on the material’s side NHC-type carbene–borane adducts and metal complexes of them can also be

The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 1194–1219, doi:10.3762/bjoc.11.134

• this account each step was performed and optimised individually in flow, with analysis and purification being accomplished off-line. The synthesis commences with the reduction of the advanced intermediate ketone 47 using a solution of pre-chilled borane–THF complex (48) to yield alcohol 49 (Scheme 8

Synthesis of nanodiamond derivatives carrying amino functions and quantification by a modified Kaiser test

• Gerald Jarre,
• Steffen Heyer,
• Elisabeth Memmel,
• Thomas Meinhardt and
• Anke Krueger

Beilstein J. Org. Chem. 2014, 10, 2729–2737, doi:10.3762/bjoc.10.288

• combustion analysis is not suitable for this type of nanodiamond derivatives. The dicyanopyrazine conjugate 4 can be submitted to a reduction of the nitrile groups using borane solution in THF. This mild yet efficient reaction leads to the complete transformation of the nitriles to amino groups as evidenced

• : negative, zetapotential: not measured as no stable colloidal solution in water was obtained. Particle size: 15 nm (acetone). Synthesis of 5: 65 mg of 4 was suspended in 5 mL BH3∙THF (1 M) and heated for 20 h under nitrogen atmosphere at 50 °C. Excess borane was decomposed by adding 2 N HCl. The diamond

Derivatives of the triaminoguanidinium ion, 3. Multiple N-functionalization of the triaminoguanidinium ion with isocyanates and isothiocyanates

• Jan Szabo,
• Kerstin Karger,
• Nicolas Bucher and
• Gerhard Maas

Beilstein J. Org. Chem. 2014, 10, 2255–2262, doi:10.3762/bjoc.10.234

• was combined with benzaldehyde and hydratropic aldehyde to furnish the corresponding tris(imines), which were converted into 1,2,3-tris(benzylamino)guanidinium salts by catalytic hydrogenation in the former, and by borane reduction in the latter case. The resulting alkyl-substituted

• no success either. According to a procedure by Casarini et al. [19] compound 5 could finally be obtained. This procedure uses dimethylaminoborane/p-toluenesulfonic acid, where the acid serves as an activator to release free borane. With a large excess of p-toluenesulfonic acid an anion exchange also

Atherton–Todd reaction: mechanism, scope and applications

• Stéphanie S. Le Corre,
• Mathieu Berchel,
• Hélène Couthon-Gourvès,
• Jean-Pierre Haelters and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2014, 10, 1166–1196, doi:10.3762/bjoc.10.117

• expected phosphoramidate was jointly isolated with 5 to 10% of thiophosphoramidate resulting from a cyclization reaction. The chiral phosphoramidates (Scheme 32-ii and iii) were tested as a chiral catalyst for the nucleophilic addition of diethylzinc [107] on benzaldehyde or for the asymmetric borane

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• the corresponding phosphine–borane complex [16][17]. The phosphine–borane complex is a stable intermediate toward the free phosphine. If necessary the boranato group can be removed by treatment with an excess of amine [18]. However, not all phosphines are prone to oxidation and show good air-stability

• preparative HPLC or recrystallization. Nucleophilic substitution of pure diastereomer (RP)-2a with methyllithium afforded the phosphine–borane (S)-4 with 94% enantiomeric excess. The substitution resulted in inversion of the configuration at the phosphorus center. Deboranation of the air stable borane adduct

• result of the reaction between bis(diethylamino)alkylphosphine 6 and ephedrine, followed by protection with borane. The subsequent stereoselective ring opening of compound 7 with an organolithium reagent gives way to acyclic products 8 with retention of configuration at the phosphorus center. These

Addition of H-phosphonates to quinine-derived carbonyl compounds. An unexpected C9 phosphonate–phosphate rearrangement and tandem intramolecular piperidine elimination

• Łukasz Górecki,
• Artur Mucha and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 883–889, doi:10.3762/bjoc.10.85

• (R/S). The homologous aldehyde can be prepared by oxidation of the double bond in a hydroboration–oxidation sequence, however, the presence of the nitrogen atoms, particularly that of the tertiary amino group of quinuclidine, may be troubleshooting [28][29]. Borane complexes with heteroaromatic and

• aliphatic amines are considered inconveniently stable in protic solvents (water, alcohols) and dissociate only at an elevated temperature [30]. Most probably, in our case the formation of the amine–borane complex proceeded faster than the hydroboration of the vinyl group. When compound 2 was reacted with

• complexed forms (borane-tertiary amino group). Again, step-by-step approach and separation of the intermediate appeared more profitable. First, the alcohol 7 was synthesized by hydroboration of the substrate with BH3·THF under an inert atmosphere followed by oxidation of the intermediate borane 5 complex

Aminofluorination of 2-alkynylanilines: a Au-catalyzed entry to fluorinated indoles

• Antonio Arcadi,
• Emanuela Pietropaolo,
• Antonello Alvino and
• Véronique Michelet

Beilstein J. Org. Chem. 2014, 10, 449–458, doi:10.3762/bjoc.10.42

• to C-3 fluorinated indole derivatives was less investigated. Fluorination of trialkylstannylindole derivatives with cesium fluoroxysulfate or Selectfluor was investigated for the synthesis of the corresponding 3-fluoroindoles [17]. A borane–tetrahydrofuran complex has been used to study the reduction

Cyclic phosphonium ionic liquids

• Sharon I. Lall-Ramnarine,
• Joshua A. Mukhlall,
• James F. Wishart,
• Robert R. Engel,
• Alicia R. Romeo,
• Masao Gohdo,
• Sharon Ramati,
• Marc Berman and
• Sophia N. Suarez

Beilstein J. Org. Chem. 2014, 10, 271–275, doi:10.3762/bjoc.10.22

• , BrMg(CH2)4MgBr and BrMg(CH2)5MgBr respectively. The resultant cyclic phosphines are air sensitive and therefore were allowed to react with BH3·THF to provide the air-stable 1-n-butylphospholane–borane and 1-n-butylphosphinane–borane complexes that were purified by silica-gel chromatography. The pure

• compounds were then treated under nitrogen with 1,4-diazabicyclo[2.2.2]octane (DABCO) at 80 °C to remove the borane, and the resultant mixture was purified in a nitrogen-filled glove box on a short silica-gel column. The pure cyclic phosphines (1-n-butylphospholane and 1-n-butylphosphinane) were allowed to

• -phenylphospholane–borane complex, followed by silica-gel chromatography and then removal of the borane with DABCO, to give the pure 1-phenylphospholane. The six-membered cyclic phosphine, which appears to be less air sensitive than the 1-butylphosphinane species, was purified in open air using a short column of

One-pot synthesis of cyanohydrin derivatives from alkyl bromides via incorporation of two one-carbon components by consecutive radical/ionic reactions

• Shuhei Sumino,
• Akira Fusano,
• Hiroyuki Okai,
• Takahide Fukuyama and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2014, 10, 150–154, doi:10.3762/bjoc.10.12

• work in collaboration with Dennis Curran has revealed that, with the use of NHC-borane [18], hydroxymethylation of aromatic iodides can be attained [19]. All these reactions consist of the combination of radical formylation with CO and ionic hydride reduction by hydride reagents (Scheme 1, reaction 1

Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C₂-symmetric building block: a strategy for the synthesis of decanolide natural products

• Bernd Schmidt and
• Oliver Kunz

Beilstein J. Org. Chem. 2013, 9, 2544–2555, doi:10.3762/bjoc.9.289

• ). With borane–dimethylsulfide complex as the reductant and 10 mol % of catalyst, no conversion was observed at −78 °C (Table 3, entry 1), whereas attempted reduction at ambient temperature (Table 3, entry 2) resulted in the formation of a complex mixture, presumably due to competing hydroboration of the

• alkenes. With borane–THF at −50 °C the reduction proceeded to completion, but gave a 1:1 mixture of diastereomers (Table 3, entry 3). With catechol borane at −78 °C conversion was again complete, but the diastereoselectivity was far from being synthetically useful (Table 3, entry 4). Due to these rather

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• strong P1 base polymer-supported BEMP gave the corresponding ether adduct which was then converted to the desired secondary amine 1.64 via direct amidation and borane-mediated reduction. Next an SNAr reaction on 2-fluoropyridine (1.66) followed by oxidation of the benzylic alcohol using immobilised

• developed, initial masking of the acid (1.104) is achieved by silylation with subsequent borane chelate formation. Addition of the amine nucleophile 1.105 under basic conditions then renders the desired product in high yield. The available patent literature however does not comment on regioselectivity

Flow Giese reaction using cyanoborohydride as a radical mediator

• Takahide Fukuyama,
• Takuji Kawamoto,
• Mikako Kobayashi and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2013, 9, 1791–1796, doi:10.3762/bjoc.9.208

• reductive radical addition reaction, better known as the Giese reaction, was historically carried out most by using tributyltin hydride as the radical mediator [8][9]. Recently borane derivatives such as borohydride reagents [10][11][12][13] or NHC-boranes [14][15][16][17][18] can be used in simple radical

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

• decyanation step. We planned to synthesize 5 by reaction of the cyanohydrin acetonide 67 with the epoxide electrophile 66 (Figure 8) [67]. The dimethyl derivative of L-malic acid was chemoselectively reduced with borane-dimethylsulfide and sodium borohydride to afford diol 69 (Scheme 18) [68]. The primary

Methylidynetrisphosphonates: Promising C₁ building block for the design of phosphate mimetics

• Vadim D. Romanenko and
• Valery P. Kukhar

Beilstein J. Org. Chem. 2013, 9, 991–1001, doi:10.3762/bjoc.9.114

• reasonable yield, but the 1-allyl-substituted trisphosphonate 12b did not undergo hydroboration with 9-BBN. However, treatment of 12b with borane in THF resulted in conversion to the primary alcohol 34 in good yield (Scheme 16) [26]. A further example of the reactivity of trisphosphonates is provided by a

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• delivers iminolactones A. The reduction with borane gives hydroxyamine 13. In this new proposal, the iminolactone A could be unstable and difficult to purify according to Tellitu’s findings [46]. Similar stability of iminolactone is documented in the literature [53][54][55]. Although we have established

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

• Vladimir Lamm Xiangcheng Pan Tsuyoshi Taniguchi Dennis P. Curran Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 USA 10.3762/bjoc.9.76 Abstract Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3

• -dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1–24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small

• scale, products are isolated by evaporation of the reaction mixture and direct chromatography. Keywords: NHC-borane; N-heterocyclic carbene borane; reduction; Introduction Reduction of carbonyl compounds is a common, fundamental chemical transformation. Among the numerous hydride reagents available

A new synthetic protocol for coumarin amino acid

• Xinyi Xu,
• Xiaosong Hu and
• Jiangyun Wang

Beilstein J. Org. Chem. 2013, 9, 254–259, doi:10.3762/bjoc.9.30

• coumarinylacetic acid, which was then reduced to an alcohol by borane-dimethyl sulfide. After the phenolic hydroxy group was protected with a tert-butyl(dimethyl)silyl group, the alcohol was converted into a bromide and was used to alkylate a glycine enolate synthon to afford an imine. All the protecting groups

Synthesis of a derivative of α-D-Glcp(1->2)-D-Galf suitable for further glycosylation and of α-D-Glcp(1->2)-D-Gal, a disaccharide fragment obtained from varianose

• Carla Marino,
• Carlos Lima,
• Karina Mariño and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2012, 8, 2142–2148, doi:10.3762/bjoc.8.241

• -2, C-3), 73.3 (CH2Ph), 72.4 (CH2Ph), 71.1 (C-5’), 69.8 (C-5), 67.8 (C-6’), 62.2 (C-6); Anal. calcd for C61H56O14: C, 72.32; H, 5.57; found: C, 72.39; H, 5.65. 2-O-(2,3,4,6-Tetra-O-benzyl-α-D-glucopyranosyl)-3,5,6-tri-O-benzoyl-α,β-D-galactofuranose (8): To a solution of bis(2-butyl-3-methyl)borane

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

• electron-deficient Lewis acid. In the case where molecular hydrogen interacts with a phosphine/borane FLP, this occurs by the formation of a phosphonium/borate ion pair (Scheme 1). For unsaturated substrates, the reaction is better described as an insertion or cycloaddition (see Scheme 2 for a

• ]. Single-crystal X-ray structure of a silver(I) triflate adduct of (PNP)Ir═C(H)Ot-Bu with most H atoms and phosphine substituents (except ipso carbon atoms) omitted for clarity. Heterolytic cleavage of H2 by a phosphine/borane FLP by H2 polarization in the P–B cavity [5][11]. Insertion of carbon dioxide

• into a phosphine/borane FLP [14]. Oxygen-atom extrusion from CO2 by a Ta(V) neopentylidene [27]. Oxygen-atom transfer from acetone at a Zr(IV) imide [28]. Alkyne cycloaddition at a Zr(IV) imide [38]. Nitrile-alkyne cross metathesis at a W(VI) nitride [40][41]. C–H and H–H addition across a zirconium(IV