N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• based on the operating transition states [37][38]. A cyclic transition state is proposed in the reaction with sodium borohydride. In this transition state, the oxygen of the sulfinyl group interacts with the boron atom, facilitating the release of the hydride, directing the attack to the Si-face of the

• imine with (RS,E) configuration. When the reduction is performed with ʟ-selectride, with the poorly coordinating metal hydride, an open transition state operates due to the bulkiness of the isobutyl groups bonded to the boron atom. In this case, the attack of the hydride takes place to the less hindered

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• (phosphines, NHC-carbenes, bisoxazolines, pyridine-oxazolines, and miscellaneous) is used. Review Catalytic systems based on phosphine ligands A pioneering work on the enantioselective addition of boron-derived carbon nucleophiles to cyclic enones was published by the group of Miyaura et al. in 2005 [32

• of the Pd-catalysed enantioselective addition of boronic acids to cyclic enones [37]. Addition of boron-derived C-nucleophiles to cyclic enones, catalysed by L2/Pd(TFA)2 [37]. Asymmetric addition of arylboronic acids to 2-cyclohexenone catalysed by L3/Pd(dba)2 [39]. Additions to different enones

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• ], superbases [6], and as ligands for metal complexation [7]. In organic synthesis, biguanides are precursors to several heterocycles [1] such as 1,3,5-triazines, pyrimidines, boron heterocycles, and benzo[f]quinazolines. The application of biguanides as catalysts has been reported mostly for the

• 90% yield. A Lewis acid-promoted cyclization (boron trifluoride etherate at 60 °C) avoided the use of high temperatures, while providing the products in comfortable yields. Dicyanamide has also been shown to react with hydroxylamine hydrochloride to form [1,2,4]oxadiazole-3,5-diamine (Scheme 29A) [49

Manganese/bipyridine-catalyzed non-directed C(sp³)–H bromination using NBS and TMSN₃

• Kumar Sneh,
• Takeru Torigoe and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2021, 17, 885–890, doi:10.3762/bjoc.17.74

• variety of functionalities, such as boron-, silicon-, nitrogen-, and oxygen-based functional groups, and in C−C bond forming reactions, such as cross-coupling reactions [1][2][3][4][5][6]. The traditional method used for the preparation of alkyl bromides is the reaction of their corresponding alkyl

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• acceptor, and thus further combines with the electron donor to form an EDA complex, mainly due to the fact that the electron acceptor in an excited state allows for stronger oxidation, to integrate with the electron donor. In 2018, Glorius and colleagues [16] reported a method for the preparation of boron

• -protected amines, have been efficiently transformed to suitable pinacol boronic esters. This simple operation without transition-metal catalysis will be widely promoted in the synthesis of important boron-containing molecules in medicine and biology. In 2019, Aggarwal and colleagues [55] proposed that the

Synthesis, structural characterization, and optical properties of benzo[f]naphtho[2,3-b]phosphoindoles

• Mio Matsumura,
• Takahiro Teramoto,
• Masato Kawakubo,
• Masatoshi Kawahata,
• Yuki Murata,
• Kentaro Yamaguchi,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2021, 17, 671–677, doi:10.3762/bjoc.17.56

• approximately 50 nm longer than that of our oxide 3 [16]. The fluorescence wavelength, including the maximum emission (λem), and the quantum yield depend on the nature of the P-modification. Phosphine oxide 3, cation 5, and boron complex 6 emitted blue fluorescence in the visible-light region, with λem at 395

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• disubstituted alkene 13 in refluxing diglyme or triglyme at 190 °C (Scheme 7) [23]. The method has been widely used for the difluorocyclopropanation of allylic alcohol derivatives [24], steroids [25], and N-Boc-protected enamides [26]. Boron-substituted difluorocyclopropanes 16 can be also obtained from 12

• cyclopropane formation did not require Et3B (Scheme 25). The work was extended to include boron-free, diastereoselective versions incorporating N-acylimidazolidinone chiral auxiliaries (Scheme 26). Cyclization reaction of phenylacetonitrile and 1,2-dibromo-1,1-difluoroethane: Kagabu et al. showed that the

Total synthesis of decarboxyaltenusin

• Lucas Warmuth,
• Aaron Weiß,
• Marco Reinhardt,
• Anna Meschkov,
• Ute Schepers and
• Joachim Podlech

Beilstein J. Org. Chem. 2021, 17, 224–228, doi:10.3762/bjoc.17.22

• -tetramethyl-1,3,2-dioxaborolane [23]. The electrophilic compound suitable for the projected cross coupling was obtained by mono-demethylation of commercially available 1-bromo-3,5-dimethoxybenzene (7) with boron tribromide (Scheme 3). A satisfactory yield of phenol 8 was observed with 0.9 equivalents of the

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• , it was transformed into (E)-vinylboronate (+)-145b in perfect stereoselectivity by using the recently developed boron-Wittig reaction with bis[(pinacolato)boryl]methane (144) [79]. By applying the Corey–Fuchs dibromoolefination and followed by Pd-catalyzed hydrogenolysis under Uenishi's conditions

• [80], compound (Z)-(+)-143a delivered the bromodiene (Z,Z)-(+)-145a in good yield and stereoselectivity. Isomerization of (Z)-(+)-143a to (E)-(+)-143b was carried out successfully using sterically hindered base DBU or DABCO. Treatment of (E)-(+)-143b with 144 using the boron-Wittig reaction [79

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• -mediated conjugated addition of methyllithium to enone 59 in the presence of boron trifluoride ether [34][35] produced desired ketone 60 in 75% yield. The resultant ketone 60 was converted to waihoensene (16) in two steps. Palladium-catalyzed carboxylative trimethylenemethane cycloaddition In 1986, Trost

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Chan–Evans–Lam N1-(het)arylation and N1-alkеnylation of 4-fluoroalkylpyrimidin-2(1H)-ones

• Viktor M. Tkachuk,
• Oleh O. Lukianov,
• Mykhailo V. Vovk,
• Isabelle Gillaizeau and
• Volodymyr A. Sukach

Beilstein J. Org. Chem. 2020, 16, 2304–2313, doi:10.3762/bjoc.16.191

• significant role in the generation of active copper-organic intermediates from boron-organic precursors [18][19][20]. Our interest in the development of N-arylation methods resonated with recent studies focused on the addition of various C-nucleophilic reagents to 4-trifluoromethylpyrimidin-2(1H)-ones I

The B & B approach: Ball-milling conjugation of dextran with phenylboronic acid (PBA)-functionalized BODIPY

• Patrizia Andreozzi,
• Lorenza Tamberi,
• Elisamaria Tasca,
• Gina Elena Giacomazzo,
• Marta Martinez,
• Mirko Severi,
• Marco Marradi,
• Stefano Cicchi,
• Sergio Moya,
• Giacomo Biagiotti and
• Barbara Richichi

Beilstein J. Org. Chem. 2020, 16, 2272–2281, doi:10.3762/bjoc.16.188

• phenylboronic acid (PBA)-functionalized boron dipyrromethene (BODIPY) applying the ball milling approach. The ball milling formation of boron esters between PBA BODIPY and dextran proved to be more efficient in terms of reaction time, amount of reactants, and labelling degree compared to the corresponding

• with small molecules, in a green and scalable process. Results and Discussion The boron dipyrromethene dye 1 bearing a phenylboronic acid moiety (PBA) at the meso position of the BODIPY core (Scheme 1) was prepared in four synthetic steps starting from 4-formylbenzeneboronic acid (2) and pyrrole (3

• conjugate (milled reaction) compared to a 0.61% w/w of 1 in the Dex-1a conjugate (conventional solution reaction) was obtained. The loading of 1 in both conjugates was also confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis which showed in Dex-1b a boron content roughly

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• ′-tetramethylethylenediamine (TMEDA) as shown in the Scheme 1. Having the compound 4 in hand, it was subjected to the cyclization in the presence of boron trifluoride to provide the tricyclohexyl-fused benzene derivative which on further dehydrogenation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) afforded 1,5,9

The biomimetic synthesis of balsaminone A and ellagic acid via oxidative dimerization

• Sharna-kay Daley and
• Nadale Downer-Riley

Beilstein J. Org. Chem. 2020, 16, 2026–2031, doi:10.3762/bjoc.16.169

• FeCl3·SiO2. Treatment of the polyphenol with PIDA (1.5 equiv) in boron trifluoride etherate (1.5 mL) at room temperature proved to be the most successful dimerization protocol, as the dimeric precursor 19 was formed in 80% yield after 16 hours. The biaryl 19 was converted quantitatively to the natural

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• -triggered complexation with boron trifluoride diethyl etherate. The resulting O,O-chelated boron complexes 11 turned out to be strong solid-state emitters featuring clear aggregation-induced emission (AIE) characteristics [61]. Encouraged by these results, we decided to attempt the reaction of 2-oxo

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• resulted in slow solvolysis of alcohol 1d with acetic acid giving mainly the corresponding acetate (not shown). Product 1d was also obtained in a similar E/Z ratio (88:12) when the ring-opening reaction was performed in dichloromethane with tetrabutylammonium bromide (TBAB) as the bromide source and boron

• can be stopped at the alcohol stage when performed in the presence of BF3·Et2O instead of CSA to afford alkene Z-13 as the major product. The use of boron trifluoride etherate as an activator combined with TBAB afforded exclusively alkene Z-13 as evidenced by TLC, but after work-up, 22% of the

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• to sorbitol. Several homogeneous catalysts were used such as mineral acids, boron phosphate and heteropolyacids (Scheme 2). Palkovits et al. studied the combination of supported noble metal catalysts based on Pt, Pd and Ru with dilute mineral acids such as phosphoric or sulfuric acid for the

• showed that the acidity is important in the conversion of lignocellulosic biomass to isosorbide and that the acid can react with the metal-supported catalyst. Another study was devoted to the use of boron phosphate for the conversion of cellulose into liquid hydrocarbon C1–C6 over Ru/C [23]. A mixture of

• sorbitan from 29% to 22% and from 5% to 3%, respectively. A similar tendency was observed in the presence of boron phosphate. This was due to the slow dissolution of boron phosphate in aqueous solution implying a release of H+ according to reaction time. They also observe an increase of isosorbide

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• -throughput screening [71] are based on the occurrence of patterns within the Lewis structure. For chemists, the Lewis structure represents both metadata for AI/ML and an essential language for communication. However, like language, the Lewis model is context dependent (aromatic bonds, boron bonding…) and

Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells

• Giacomo Mari,
• Lucia De Crescentini,
• Serena Benedetti,
• Francesco Palma,
• Stefania Santeusanio and
• Fabio Mantellini

Beilstein J. Org. Chem. 2020, 16, 1606–1616, doi:10.3762/bjoc.16.133

• interest, the hydrazono-DHBERs 2a–n were further treated with 2.0 equivalents of sodium boron hydride at room temperature in methanol. The reaction furnishes the corresponding hydrazono-THBERs 3a–n in good yields (77–96%, Scheme 3). It is noteworthy that in these conditions, only the iminium moiety is

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• silane is very sensitive to Lewis bases and accordingly it was used as a precursor of difluorocarbene, which can react with enol ethers [19][20] (Scheme 1). We showed that this silane could be involved in the radical chain hydrofluoroalkylation of electron-deficient alkenes, using a boron hydride as a

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

• Kazuyuki Sato,
• Akira Kawasaki,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2020, 16, 1411–1417, doi:10.3762/bjoc.16.117

• synthesized and investigated for their photochemical properties. The introduction of a fluorine substituent into 3,5-diarylisoxazoles led to an increase of fluorescence intensity and exhibited a redshift in the emission intensity. α-Fluorinated boron ketoiminates (F-BKIs) were also synthesized via a ring

• -opening reaction of 4-fluoroisoxazoles and exhibited highly fluorescent luminescence and aggregation-induced emission (AIE), showing promise as a new fluorophore. Keywords: aggregation-induced emission; boron ketoiminates; fluorescent probe; α-fluorinated boron ketoiminates; 4-fluoroisoxazoles

• fluorescent luminescence characteristics of 4-fluoroisoxazoles, the synthesis of α-fluorinated boron ketoiminates (F-BKIs), and their photochemical properties. Results and Discussion Synthesis and optical properties of 4-fluorinated isoxazoles Although there is a large number of fluorescent molecules

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

• Alexander V. Nyuchev,
• Ting Wan,
• Borja Cendón,
• Carlo Sambiagio,
• Job J. C. Struijs,
• Michelle Ho,
• Moisés Gulías,
• Ying Wang and
• Timothy Noël

Beilstein J. Org. Chem. 2020, 16, 1305–1312, doi:10.3762/bjoc.16.111

• poor yields. Other synthetically useful substituents, including cyano, nitro, phenylsulphonyl, (pinacolato)boron, and alkyl groups could be tolerated in the reaction (24–30), leading to a yield range between 26 and 65%. The trifluoromethoxylation of pyridine, pyrimidine, and thiophene derivatives also

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• yields of 25–35% and with a radiochemical purity of more than 99%. The 18F-labeling of 4-borono-ᴅ,ʟ-phenylalanine (BPA) provided a potential tool for cancer treatment by boron neutron capture therapy [53] (Scheme 16). The syntheses of a variety of clinically relevant radiotracers including protected 4

• used in PET due to its relatively long half-life (109 min). In this section we highlight two selected 18FPhe derivatives which are used for PET tumor detection. 4-Borono-2-[18F]fluoro-ᴅ,ʟ-phenylalanine ([18F]FBPA, 70), is a fluorinated derivative of the parent compound designed for boron neutron

Suzuki–Miyaura cross coupling is not an informative reaction to demonstrate the performance of new solvents

• James Sherwood

Beilstein J. Org. Chem. 2020, 16, 1001–1005, doi:10.3762/bjoc.16.89

• the key fundamental principles of boron and palladium speciation and the role of the base in the Suzuki–Miyaura reaction. For researchers developing safer solvents, the Mizoroki–Heck reaction is a more suitable cross-coupling methodology to demonstrate solvent performance [28]. The reaction kinetics