[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• -2-yl, quinolin-2-yl, 5,6-dihydro-4H-1,3-oxazin-2-yl). Such sydnones reacted with potassium 2-substituted acetylene trifluoroborates under boron trifluoride diethyl etherate catalysis to give corresponding pyrazolo[3',4':4,5][1,2]azaborolo[2,3-a]pyridin-5-ium-4-uides (or quinolin-5-ium-4-uide) in

• -1,3,5-trisubstitutedpyrazole (Scheme 11). Overall therefore, a nitrogen atom in the sydnone 4-heterocyclyl substituent (especially 2-pyridyl) acts as powerful activating group enabling cycloaddition reaction under ambient conditions and also influencing the regioselectivity. Boron carrying two alkynyl

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• utility is limited since it requires highly reactive boron compounds as nucleophiles. Symmetrical biphenyls 3’ can be generated from the corresponding symmetrically substituted diaryliodonium salts 1 and bis(pinacolato)diboron as demonstrated by Muñiz and co-workers [25]. In the first step, a mild carbon

• –boron bond formation gives one equivalent of arylboronic ester 4 and an iodoarene 2 through a metal-free boron arylation. Subsequent cross coupling under Suzuki conditions affords symmetrical biphenyls 3’ in good yields. Due to the temporary introduction and cleavage of the boron moiety the formal atom

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• Diels–Alder reaction. Ghosh’s group reported an exclusive peri-, regio-, and stereoselective cycloaddition reaction of 5H-benzo[7]annulen-5-one (Scheme 35) [137]. The intermolecular [4 + 2] cycloaddition of 2,3-benzotropone (12) with cyclopentadiene (202) in the presence of boron trifluoride occurred

• depicted in Scheme 38 (Scheme 45) [161]. Sato’s group reported the synthesis of 7-hydroxy-2,3-benzotropone (241) via the ring expansion pathway of β-naphthoquinone (280) with diazomethane under various conditions and hydrolysis steps (Scheme 46) [169]. The boron trifluoride etherate-promoted ring expansion

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

Hypervalent iodine-guided electrophilic substitution: para-selective substitution across aryl iodonium compounds with benzyl groups

• Cyrus Mowdawalla,
• Faiz Ahmed,
• Tian Li,
• Kiet Pham,
• Loma Dave,
• Grace Kim and
• I. F. Dempsey Hyatt

Beilstein J. Org. Chem. 2018, 14, 1039–1045, doi:10.3762/bjoc.14.91

• mechanism could be occurring with metalloid groups such as silicon and boron. Hypervalent iodine reagents such as Zefirov’s reagent, cyclic iodonium reagents, iodosobenzene/BF3, and PhI(OAc)2/BF3 or triflate-based activators were tested. A desirable facet of the reported reaction is that iodine(I) is

• unreacted BnTMS or BnBF3K. The results in Table 1 show that silyl groups seem to be superior to boron groups for the reaction to afford a good yield. The solvent choices were made based on low nucleophilicity and polarity being high enough to dissolve the hypervalent iodine starting material. Surprisingly

• solubility of trifluoroborates in the solvents used. The displacement of silyl and boron groups with hypervalent iodine seems to suggest that a transmetallation event from Si/B to I is occurring rather than an addition reaction to the unsaturation of the benzyl group followed by elimination of the metalloid

Preparation, structure, and reactivity of bicyclic benziodazole: a new hypervalent iodine heterocycle

• Akira Yoshimura,
• Michael T. Shea,
• Cody L. Makitalo,
• Melissa E. Jarvi,
• Gregory T. Rohde,
• Akio Saito,
• Mekhman S. Yusubov and
• Viktor V. Zhdankin

Beilstein J. Org. Chem. 2018, 14, 1016–1020, doi:10.3762/bjoc.14.87

• and peptides [23][24][25]. Numerous examples of five-membered hypervalent iodine(III) heterocycles containing other than oxygen heteroatoms, such as sulfur [26], boron [27][28], phosphorous [29], or nitrogen [30][31][32], have been synthesized and characterized by X-ray crystallography. In particular

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones

• Keshaba N. Parida,
• Gulab K. Pathe,
• Shimon Maksymenko and
• Alex M. Szpilman

Beilstein J. Org. Chem. 2018, 14, 992–997, doi:10.3762/bjoc.14.84

• challenging cross-coupling of two dissimilar ketone enolates. In this context Hirao achieved the intermolecular cross-coupling by taking advantage of the different oxidation potentials of boron enolates and trimethylsilyl enol ethers to achieve selectivity with vanadium (V, 0.625 equiv) as the oxidant (Scheme

•  1d) [28][29][30]. The final example is the intermolecular cross-coupling of two dissimilar trimethylsilyl enol ethers described herein (Scheme 1e). Results and Discussion Previously we have established that as little as 1.25 equiv of Koser’s reagent and 1.25 equiv of boron trifluoride in

An air-stable bisboron complex: a practical bidentate Lewis acid catalyst

• Longcheng Hong,
• Sebastian Ahles,
• Andreas H. Heindl,
• Gastelle Tiétcha,
• Andrey Petrov,
• Zhenpin Lu,
• Christian Logemann and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 618–625, doi:10.3762/bjoc.14.48

• applicability [17]. To overcome this limitation we herein present a new catalyst (Scheme 1, B) with reasonable stability to air and moisture, which can be handled under ambient conditions and prepared with standard laboratory equipment. Results and Discussion Generally, the reactivity of boron Lewis acids is

• attributed to the free vacant p-orbital of the boron atom leading to further transformations, such as decomposition via radicals (O2), reactions with nucleophiles (H2O) as well as the formations of adducts. From this perspective, a suitable Lewis base may form a Lewis complex and subsequently occupy the p

• -orbital of the boron atom. This may prevent the boron compound from decomposition as well as hydrolysis and provide a practical Lewis acid catalyst for organic reactions. To test the hypothesis, several Lewis bases were subjected to the coordination reaction with the bidentate bisboron catalyst, 5,10

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• -based boron enolates to aromatic and aliphatic aldehydes to form anti-2-pentafluoro-λ6-sulfanyl-3-hydroxyalkyl-carboxylic acid esters [29]. Quite similar results were published independently by Carreira et al. a couple of weeks before us [30]. Recently, we discovered that silylated enolates can be

• -arrangement (Figure 1). Such an arrangement was found in the crystalline state of an anti-aldol product we obtained as a result of a boron-mediated aldol reaction of the benzyl ester analog of compound 1 with benzaldehyde [29]. This product and a couple of its aryl-substituted analogs exhibited coupling

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• purity [30]. Due to the difficulty to address simultaneously these different points, numerous light emitting materials have been revisited several times, providing different electrical and optical device characteristics. 2. Boron-containing TADF emitters Boron-containing molecules have been extensively

• investigated in organic electronics [31] as these materials are characterized by a remarkable electron mobility resulting from the presence of a vacant p-orbital on the boron atom [32][33]. Triarylboron compounds are also strong electron acceptors, justifying that numerous groups developed TADF emitters using

• be realized by totally blocking the structure, what was done with B9 and B10 in which two of the three aromatic rings of triphenylamine were connected to the boron center [39]. By elongating the π-conjugation of the electron-donating group in B10 compared to B9, a more delocalized HOMO level could be

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• isopropylidene group furnished diol 13. Regioselective boron trifluoride diethyl etherate-promoted glycosylation of the 6-OH group in 13 with Kdo-fluoride donor 14 afforded an inseparable mixture of α- and β-anomeric products (α/β = 9:1) [78]. Phosphitylation of the remaining OH group in position 4’ and facile

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations

• Aymen Skhiri,
• Ridha Ben Salem,
• Jean-François Soulé and
• Henri Doucet

Beilstein J. Org. Chem. 2017, 13, 2862–2868, doi:10.3762/bjoc.13.278

• ][5][6][7][8][9], Suzuki [10][11][12][13][14][15][16][17][18][19], or Kumada [20] couplings [21] (Scheme 1a and b). However, all these procedures require the preparation of an organometallic or a boron derivative of one of the coupling partners, and provide an organometallic salt (MX) as waste. In

Diastereoselective Mannich reactions of pseudo-C₂-symmetric glutarimide with activated imines

• Tatsuya Ishikawa,
• Tomoko Kawasaki-Takasuka,
• Toshio Kubota and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 2473–2477, doi:10.3762/bjoc.13.244

• , Nakanarusawa 4-12-1, Hitachi 316-8511, Japan 10.3762/bjoc.13.244 Abstract As an extension of the boron enolate-based aldol reactions, the oxazolidinone-installed bisimide 1a from 3-(trifluoromethyl)glutaric acid was employed for Mannich reactions with tosylated imines 2 as electrophiles to successfully obtain

• couple of routes to get successful access to such target molecules with a variety of substituents at the 2-position [1][2][3]. Previously, the oxazolidinone-installed bisimide 1a was employed for the crossed aldol reactions by the way of boron enolate which allowed the isolation of optically active

Structure–property relationships and third-order nonlinearities in diketopyrrolopyrrole based D–π–A–π–D molecules

• Jan Podlesný,
• Lenka Dokládalová,
• Oldřich Pytela,
• Adam Urbanec,
• Milan Klikar,
• Numan Almonasy,
• Tomáš Mikysek,
• Jaroslav Jedryka,
• Iwan V. Kityk and
• Filip Bureš

Beilstein J. Org. Chem. 2017, 13, 2374–2384, doi:10.3762/bjoc.13.235

• boron derivatives [34][35]. Twofold Sonogashira cross-coupling was utilized towards chromophores 1b–5b. All cross-coupling reactions were carried out in THF with PdCl2(PPh3)2 as palladium precatalyst. The reaction time was approximately 24 hours to achieve sufficient conversion (32–73%). Despite bearing

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives

• Mio Matsumura,
• Mizuki Yamada,
• Atsuya Muranaka,
• Misae Kanai,
• Naoki Kakusawa,
• Daisuke Hashizume,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2017, 13, 2304–2309, doi:10.3762/bjoc.13.226

• -b]phosphole dioxides (Figure 1A) [25][26] and benzophosphole-fused tetracyclic heteroacenes, containing boron (B) [27][28][29], silicon (Si) [30], oxygen (O) [31], and sulfur (S) [32][33][34] (Figure 1B), were synthesized and their physical properties were studied. However, to the best of our

• NMR signals of gold and boron complexes 8 and 9 were observed at δ = 6.0 and 11.5 ppm, respectively. These results show that the electronic nature of the phosphorus atoms is similar to that of the oxidized species 4–7 (δ = 6.0–27.0 ppm). In the IR spectrum of 4 in KBr, a strong absorption for P=O

• electron-accepting properties. This red shift related to methylation of a phosphorus atom is in line with other earlier studies [10][18][33]. The fluorescence intensity of 7 (Ф = 67%) was as strong as that of phosphine oxide 4. The gold and boron complexes (8 and 9, respectively) showed contrasting

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

• Satoru Mori and
• Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

• composed of three isoindoline units. The only central element of subphthalocyanine is boron, and it has a ligand in the axial direction on the boron. Since subphthalocyanines have excellent spectroscopic properties and a unique three-dimensional structure, it is expected that they will be applied to

• solubility due to the influence of fluorine and are easy to handle, it is expected that various derivatives as well as TFEO-Pcs will be developed. TFEO-subPc is synthesized by cyclotrimerisation of tetrakis(trifluoroethoxy)phthalonitrile (2) in the presence of boron trichloride in p-xylene under reflux

• synthesized by an unsymmetrical synthesis using diiodophthalonitrile 35 and trifluoroethoxyphthalonitrile 2, and then iodides were converted to cyano groups by a coupling reaction. Finally, dicyanophthalocyanine 37 was reacted with 2 in the presence of boron trichloride to obtain trifluoroethoxy-substituted

Curcuminoid–BF₂ complexes: Synthesis, fluorescence and optimization of BF₂ group cleavage

• Henning Weiss,
• Jeannine Reichel,
• Helmar Görls,
• Kilian Rolf Anton Schneider,
• Mathias Micheel,
• Michael Pröhl,
• Michael Gottschaldt,
• Benjamin Dietzek and
• Wolfgang Weigand

Beilstein J. Org. Chem. 2017, 13, 2264–2272, doi:10.3762/bjoc.13.223

• yields strongly decrease when employing other aldehydes [12]. This procedure also requires a rather extensive work-up including several extraction steps and chromatography [8]. A second, more recent approach first published by Rao et al. relies on boron trifluoride as the complexing agent [13]. The

• around −140 ppm, while 11B{1H} NMR signals appear as up to 3 ppm broad singlets at about +0.9 ppm. No coupling between 19F and 11B nuclei was observed because of the high quadrupole moment of the 11B nucleus. Due to the high relative mass difference between both naturally occurring boron isotopes

• solutions. All BF2 complexes show the expected tetrahedral coordination sphere around the boron atom and the all-trans geometry of the olefinic double bonds (Figure 1). Bond lengths and angles around the boron atom are in good accordance to values published for similar complexes [9]. One aromatic ring of 2f

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• side reactions is not due to bromotrimethylsilane but to the sensitivity of the product to acidic conditions that are induced by the acidity of the phosphonic acid functional group. 3.4. Dealkylation with boron reagents Dealkylation of dialkyl phosphonates could also be performed using C6H11BCl2 [201

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• reacted with 1,2-anhydro donor 80. It was assumed that this reaction proceeds via the oxacarbenium ion tethered to a tetracoordinated boronate ester. The subsequent glycosylation then proceeds regioselectively from the less-hindered boron–oxygen bond (see intermediate A). In this case, where gluco

• . Conversely, the galacto-configured boronic ester acceptor 82 was used, the α-(1→6)-linked product 83 was formed in 70% yield. Again, the regioselectivity of glycosylation is driven by the less-hindered boron–oxygen bond, which is from C-6 face in the case of galactose (intermediate B, Scheme 19). In the case

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• be asymmetric α-phopshorylation approaches or the introduction of other heteroatoms (e.g., boron), which are all transformations that are without doubt important, but so far much less systematically addressed as most of the examples we showed herein. We are therefore convinced that the field of

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

• against competing microorganisms was not the evolutionary driver for the emergence of the toxin. It is generally assumed in the literature that mycolactones reach their cellular targets by passive diffusion [91]. Based on competition experiments with the fluorescent, boron-dipyrromethene (BODIPY)-labeled

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

• Stephan Scheeff and
• Dirk Menche

Beilstein J. Org. Chem. 2017, 13, 1085–1098, doi:10.3762/bjoc.13.108

• a boron-mediated anti-aldol reaction [67] of lactate-derived ethyl ketone 13 with aldehyde 12, which in turn was available from aldehyde 9 by HWE olefination. This Paterson aldol reaction and related aldol reactions, which have been amply used by the Menche group [68][69][70], proceeded with

• ’ during thiazole formation on large scale, requiring an oxidation–reduction sequence (90%) in this case. Completion of the total synthesis After evaluation of several strategies, the assembly of the two northern fragments 4 and 5 could be realized by an aldol condensation, involving a boron-mediated aldol

• full stereochemistry in the first place. The various approaches discussed within this manuscript show the various tactics and strategies that may be employed in complex polyketide synthesis. Notable features of the total synthesis by the Menche group include the robustness of boron mediated aldol

Substitution of fluorine in M[C₆F₅BF₃] with organolithium compounds: distinctions between O- and N-nucleophiles

• Anton Yu. Shabalin,
• Nicolay Yu. Adonin and
• Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

• Bu, the nucleophilic substitution of the fluorine atom at the para position to boron is the predominant route. When R = Ph, the ratio M[4-RC6F4BF3]/M[2-RC6F4BF3] is ca. 1:1. Substitution of the fluorine atom at the ortho position to boron is solely caused by the coordination of RLi via the lithium

• ]. Over the last 15 years, we reported the successful application of polyfluorinated organoborates K[RC6F4BF3], K[C6F5B(OMe)3] and K[CF2=CFBF3] as boron-containing reagents in the Pd-catalyzed cross-coupling reactions with C-electrophiles [22][23][24][25][26][27]. Nowadays a common approach to these

• compounds is based on the transformation of polyfluoroarenes under the action of appropriate reagents into the corresponding organometallic derivatives followed by treating them with suitable boron-containing electrophiles (Scheme 1) [28][29]. In order to further expand this powerful tool for the

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

• Stephen Hill and
• M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

• to improve the PL properties of CDs, the use of boron as an additive, which is an electron-accepting element, has also been explored by Hao et al. [38]. The CDs were produced by the addition of boric acid (B(OH)3) into the hydrothermal carbonisation of glucose, using a Teflon autoclave at 180 °C for

• 12 h (Scheme 7). The resultant fluorescent nanoparticles had an average diameter of 4 nm and were negatively charged with ZP values of −40.7 mV. XPS and FTIR analysis confirmed the presence of B in the CD structure. Although, the addition of boron did not change the typical blue fluorescence profile

Continuous N-alkylation reactions of amino alcohols using γ-Al₂O₃ and supercritical CO₂: unexpected formation of cyclic ureas and urethanes by reaction with CO₂

• Emilia S. Streng,
• Darren S. Lee,
• Michael W. George and
• Martyn Poliakoff

Beilstein J. Org. Chem. 2017, 13, 329–337, doi:10.3762/bjoc.13.36

• ., boron salts from reductive amination [4]. Hydrogenation offers a greener approach but is often only applicable to simple substrates due to chemoselectivity issues. An approach that has received much attention recently is the concept of hydrogen borrowing catalysis [5][6][7][8][9][10][11][12][13][14][15