Synthesis of six-membered silacycles by borane-catalyzed double sila-Friedel–Crafts reaction

• Yafang Dong,
• Masahiko Sakai,
• Kazuto Fuji,
• Kohei Sekine and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2020, 16, 409–414, doi:10.3762/bjoc.16.39

• , Fukuoka 816-8580, Japan 10.3762/bjoc.16.39 Abstract We have developed a catalytic synthetic method to prepare phenoxasilins. A borane-catalyzed double sila-Friedel–Crafts reaction between amino group-containing diaryl ethers and dihydrosilanes can be used to prepare a variety of phenoxasilin derivatives

• been demonstrated. Keywords: borane; cyclic compound; organosilane; sila-Friedel–Crafts; silylation; Introduction Six-membered silacyclic compounds, such as phenoxasilin and phenothiasilin derivatives, are attractive compounds for applications as organic electronic materials [1][2][3][4], ligands [5

• benzosiloles [39]. We have also contributed to the synthesis of silafluorenes from biphenyls and dihydrosilanes using a borane-catalyzed double sila-Friedel–Crafts reaction [40][41]. Subsequently, we envisaged that the catalytic reaction between diaryl ethers and dihydrosilanes may be a useful protocol to

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• them are easily oxidized, hence the reactions are often conducted under inert conditions. Alternatively, the phosphine can be protected as a borane adduct and thereafter, the protecting group is ultimately removed to liberate the free ligand. This method has been developed by Imamoto et al. [51][52

• advantage of this fact by synthesizing a class of N-tethered phosphine imidazole ligands (Scheme 16, route A). The lithiation of the presynthesized chloromethylimidazolium iodide 82 and subsequent trapping with borane-protected di-tert-butylphosphine gave the imidazolium borane adduct 83a. The subsequent

• precursors. However, asymmetric synthesis can be used as strategy to introduce stereogenic P-atoms into the ligand’s backbone. The borane complexation approach is a unique stereoselective way for introducing a P-stereogenic center. Benoit et al. [2] reported on the synthesis of 2-phenyl-1,3,2

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• (III) chloride in methanol in 88% yield (Scheme 1). The synthesis of allylic alcohol 11, a regioisomer of 6, started again from (1R)-α-pinene (1, Scheme 2). Hydroboration of (1R)-α-pinene with borane–dimethyl sulfide adduct (BMS) and crystallization of the product diisopinocampheylborane (dIpc2BH, 84

• % yield. The allylic diphenylphosphine oxide 21 was subjected to the hydroboration–oxidation reaction introducing stereoselectively the hydroxy group. Hydroboration was carried out with an excess of borane–dimethyl sulfide adduct followed by the oxidation step. The standard C–B bond oxidation protocol

• borane–dimethyl sulfide adduct in THF at 50 ºC. Oxidation of the alkylborane with mCPBA gave the desired alcohol 27 in 51% overall yield. Finally, diastereomeric endocyclic allylic alcohols 16 and 18 were treated with chlorodiphenylphosphine in the presence of DMAP to produce diphenylphosphinites 28 and

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy

• Daniela Imperio,
• Erika Del Grosso,
• Silvia Fallarini,
• Grazia Lombardi and
• Luigi Panza

Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135

• the desired product 7 by the simple treatment of 6 with an excess of borane-THF complex (5 molar equiv) followed by quenching with water, while in the same conditions compound 5 again gave extensive decomposition. These conditions allowed the isolation of the cyclic anomeric boron analogue 7 in

• stereoselectivity in the hydroboration reaction we hypothesized the transition states bearing to the two epimers. We assumed that borane would react firstly with the free hydroxy group generating an intermediate alkoxyborane, and that the hydroboration reaction occurs intramolecularly on such intermediate. Based on

Stereo- and regioselective hydroboration of 1-exo-methylene pyranoses: discovery of aryltriazolylmethyl C-galactopyranosides as selective galectin-1 inhibitors

• Alexander Dahlqvist,
• Axel Furevi,
• Niklas Warlin,
• Hakon Leffler and
• Ulf J. Nilsson

Beilstein J. Org. Chem. 2019, 15, 1046–1060, doi:10.3762/bjoc.15.102

• route to 2-deoxyhepuloses 3, 5 and 7 [27][28][29][30]. The hydroboration of enol ethers 2, 4, and 6 with borane dimethyl sulfide in THF, followed by oxidation using hydrogen peroxide and sodium hydroxide gave 2-deoxygalactoheptulose 3 and 2-deoxymannoheptulose 5 in good yields (89% and 78%) and with

• -galactoheptulose (3): Compound 2 (3.66 g, 6.82 mmol) was dissolved in dry tetrahydrofuran (130 mL) under nitrogen and cooled to 0 °C. Borane dimethyl sulfide complex in dry tetrahydrofuran (4.78 mL, 9.55 mmol, 2 M) was added slowly, and the reaction was kept at 0 °C for 2 h. The reaction mixture went from light

• yellow to colorless during the addition of the borane dimethyl sulfide complex. Upon complete consumption of 2, distilled water (15 mL) was added to the reaction mixture slowly (dropwise at first) while vigorous gas evolution was observed. After completion of the gas evolution, sodium hydroxide (14 mL

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• to that for 1 and 2 [37]. Asymmetric reduction of the carbonyl group of 2’-bromobenzophenone (a) with borane dimethyl sulfide in the presence of (S)-(−)-2-methyl-CBS-oxazaborolidine catalyst gave (S)-(2-bromophenyl)(phenyl)methanol (S)-b in 93% yield and 94% ee (Scheme 2 and Figure S1 in Supporting

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• cyclopropanol by Cottle [7], the most popular methods for the preparation of cyclopropanols rely on the transformation of enolates [8][9], silyl enol ether [10][11][12], vinyl borane [13][14][15][16][17], Fischer carbene addition [18], addition of nucleophiles to carbonyl groups [19][20][21][22][23][24][25

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

• Eloi P. Coutant,
• Vincent Hervin,
• Glwadys Gagnot,
• Candice Ford,
• Racha Baatallah and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

• exceedingly slow reaction requiring repeated additions of trimethylamine–borane complex on a solution of compound 2a in diethyl ether saturated with hydrogen chloride (ether containing trifluoromethanesulfonic acid was also tried). This led only to a 40% yield probably because of the occurrence of stable

Synthesis of mono-functionalized S-diazocines via intramolecular Baeyer–Mills reactions

• Miriam Schehr,
• Daniel Hugenbusch,
• Tobias Moje,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2018, 14, 2799–2804, doi:10.3762/bjoc.14.257

• precursor 16 was reduced using a borane tetrahydrofuran complex and immediately reacted in the Baeyer–Mills reaction without further purification. In Table 2 the yields using the Baeyer–Mills reaction are compared with the yields using the reductive azo condensation with lead [17]. Compared to the reductive

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• prepared in 87% yield from the reaction of PCl3 and MgBr(CH2)6CH=CH2. Following the addition of H3B·SMe2, the phosphine borane 1·BH3 can be isolated in 65–85% yields [31], as shown in Scheme 2. It is critical to avoid an excess of H3B·SMe2, as this brings the C=C units into play. In fact, when

• singlets (14.0 ppm) was typical of a terminal methyl group. Based upon these data, and the integration of the 1H NMR spectrum, the oil was assigned as the hydrogenated phosphine borane H3B·P(n-C8H17)3 (4·BH3), a known compound [33]. The yield was only 1%. Next, another colorless oil eluted. The 1H NMR and

• eight with an intensity ratio of approximately 2:1. The less intense set resembled the signals arising from the n-octyl groups in 4·BH3. The more intense set was very similar to the signals arising from the cyclic substructures of 6·2BH3 (described below) and a phosphine borane reported earlier [34

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• -oxazaborolidine-catalyzed asymmetric borane reduction of β-keto sulfides 68 for the synthesis of β-hydroxy sulfides with high enantiomeric purity (Scheme 20) [54][55]. The enantioselectivity was highly dependent on the nature and bulkiness of the substituents on both ends of the carbonyl group. While the

• aromatic thiols. Ring-opening reactions of cyclohexene oxide with thiols by using CPs 1-Eu and 2-Tb. CBS-oxazaborolidine-catalyzed borane reduction of β-keto sulfides. Preparation of β-hydroxy sulfides via connectivity. Baker’s yeast-catalyzed reduction of sulfenylated β-ketoesters. Sodium-mediated ring

Visible light-mediated difluoroalkylation of electron-deficient alkenes

• Vyacheslav I. Supranovich,
• Vitalij V. Levin,
• Marina I. Struchkova,
• Jinbo Hu and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139

• carbene/borane complex and 400 nm light [48]. Results and Discussion Iodide 1a was selected as a model substrate and its reaction with tert-butyl acrylate (2a) was evaluated in the presence of various boron hydrides (Table 1). The reaction was performed in methanol with irradiation by a strip of blue

• product 3a was isolated in 83% yield (Table 1, entry 6). N,N'-Dimethylimidazolidene borane complex (NHC·BH3) was also efficient (Table 1, entry 5), but because of availability and cost issues, sodium cyanoborohydride was used for further studies. We also evaluated the photoredox-mediated

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• : ITO/MoO3 (2 nm)/1,4-bis(1-naphthylphenylamino)biphenyl (NPB) (25 nm)/1,3-bis(9-carbazolyl)benzene (mCP) (8 nm)/complex 8 or 9 (40 nm)/tris[3-(3-pyridyl)mesityl]borane (3TPyMB) (50 nm)/LiF (1 nm)/Al. The OLED based on 8 displayed orange-red electroluminescence (EL) with EQE of 19.0%, current efficiency

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

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

• reductive opening of benzylidene acetal using the borane−THF complex in the presence of Bu2BOTf. Regioselective TMSOTf-catalysed glycosylation of the diol 4 by the imidate donor 3 resulted in the formation of a single product, the β(1→6)-linked disaccharide 5. After the 2’-N-Fmoc group in 5 was removed with

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

• tetracyclic moieties are planar. The benzophosphole-fused indoles, such as phosphine oxide, phospholium salt, and borane complex, exhibited strong photoluminescence in dichloromethane (Φ = 67–75%). Keywords: benzophospholo[3,2-b]indole; DFT calculation; molecular structure; phosphole derivatives

• benzophosphole-fused indole derivative and its various functionalized analogs such as the corresponding phosphine oxide, phosphonium salt, and borane–phosphine complex. Results and Discussion The synthesis of the parent tetracyclic molecule 10-phenyl-[1]benzophospholo[3,2-b]-N-methylindole (3), is shown in

• , respectively. The reaction of 3 with methyl triflate afforded phospholium triflate 7. Phosphole 3 was treated with chloro(dimethyl sulfide)gold in CH2Cl2, resulting in P-complexation and thus affording the gold complex 8. The borane complex 9 was readily prepared from 3 by treating with borane in THF. The

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

• that finally led to the formation of the phosphonodiamidate 100. The reduction of the nitro function and the hydrolysis under acidic conditions of the phosphonodiamide produced the phosphonic acid 101 [211]. As a last example, lithiated diaminophosphine borane 102 was added to imine to produce the bis

• (diethylamino)phosphone borane 103 (Figure 28C). Then acidic hydrolysis conditions and likely air oxidation produced the phosphonic acid 104 [209]. Phosphonodiamide, which is more robust than phosphonate towards some nucleophilic species like a phosphide anion (R2P-Li), was used to prepare triarylphosphine

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

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• amides 4a–c employing a THF solution of borane (yields 82–93%; see Supporting Information File 1 and Scheme 2). The synthesis of N-(2-aminobenzyl)amides 4a–k was achieved by selective N-acylation of 2-ABA or its N-substituted derivatives 3a–c, whose preparation is depicted in Scheme 2. In spite of the

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

• any traces of water which were shown to lead to unfavourable isomerization pathways. Finally, an oxazaborolidine-assisted borane reduction [78] set the stereogenic center at C15 and global deprotection gave synthetic archazolid A, which proved to be fully identical with a natural sample, thus

• Scheme 9. After reduction the alcohol was protected with TIPS and the TBS ether was cleaved by acetic acid to get to the primary alcohol 43. The reduction with (S)-alpine borane was highly diastereoselective (dr > 20:1). Following this sequence over 6 steps the two stereogenic centers at C7 and C8 were

Highly reactive, liquid diacrylamides via synergistic combination of spatially arranged curing moieties

• Maximilian Maier,
• Magnus S. Schmidt,
• Markus Ringwald and
• Christoph P. Fik

Beilstein J. Org. Chem. 2017, 13, 372–383, doi:10.3762/bjoc.13.40

• synthesis of 12 and other similar derivatives through a multistep reaction with the final step comprising the treatment of N,N'-dipropylperhydropyridazine-3,6-dione with a borane solution in THF [31]. Considering the high reactivity of 7 and the assumption, that the allylic double bond to the halide is

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• case the two-step protocol is followed by a lactamization and the one-pot reduction of ester and lactam groups of 18. The authors proposed a reductive anionic chain mechanism described in Scheme 10. The exposure of 14a to BH3 generates a borane–amine complex 20 whose fragmentation could be promoted by

• NaBH4. The resulting imine 21 is reduced by BH3 with the help of the cyanoborohydride anion. The formed anion 22 abstracts a proton from complex 20 to produce 23 or 24 and regenerate 21 and BH3CN−. A set of experiments supports this proposal. Notably, borane is the major hydride source for the reduction

• , malononitriles are reacting with a slight excess of NHC-borane 71, in refluxing t-BuOH with DTBP (di-tert-butylperoxide) as radical initiator. The yields are attractive while roughly comparable amounts of boryl nitriles 74 and 75 are formed (Scheme 23). Malononitriles 72d,e are successfully reduced to 73d,e

From betaines to anionic N-heterocyclic carbenes. Borane, gold, rhodium, and nickel complexes starting from an imidazoliumphenolate and its carbene tautomer

• Ming Liu,
• Jan C. Namyslo,
• Martin Nieger,
• Mika Polamo and
• Andreas Schmidt

Beilstein J. Org. Chem. 2016, 12, 2673–2681, doi:10.3762/bjoc.12.264

• .12.264 Abstract The mesomeric betaine imidazolium-1-ylphenolate forms a borane adduct with tris(pentafluorophenyl)borane by coordination with the phenolate oxygen, whereas its NHC tautomer 1-(2-phenol)imidazol-2-ylidene reacts with (triphenylphosphine)gold(I) chloride to give the cationic NHC complex [Au

• ppm. Minute traces of water protonate the anionic NHC 7 spontaneously to give 6A/B without any traces of decomposition products. The betaine 6A reacted with tris(pentafluorophenyl)borane in dioxane at reflux temperature to give the borane adduct 8. The proton attached to C-2 of the imidazolium ring

• (crystallographic numbering, cf. Figure 2: C9) is clearly detectable at δ = 9.22 ppm in DMSO-d6, while the boron and fluorine atoms give resonance frequencies at δ = −3.45 ppm, and δ = −133.91, −159.97, −165.18 ppm in the 11B NMR and 19F NMR spectra, respectively. A single crystal X-ray analysis of the borane

A direct method for the N-tetraalkylation of azamacrocycles

• Andrew J. Counsell,
• Angus T. Jones,
• Matthew H. Todd and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2016, 12, 2457–2461, doi:10.3762/bjoc.12.239

• quaternary amine species. A number of alternative approaches have been investigated, with differing degrees of success. For example Alcock et al. deployed a two-step route using acid chlorides to first form an intermediate amide, and then reduced this with borane in THF to the tertiary amine; yields were

A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus

• Jan Rinkel,
• Patrick Rabe,
• Laura zur Horst and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 2317–2324, doi:10.3762/bjoc.12.225

• proceeds via (R)- or (S)-6, by determination in which of the distinguishable diastereotopic positions the label ends up. The synthesis of the two enantiomers of (1-2H)GPP (Scheme S1, Supporting Information File 1) was performed by Alpine borane reduction [29] (both enantiomers of this reagent are