Synthesis of novel fluorinated building blocks via halofluorination and related reactions

• Attila Márió Remete,
• Tamás T. Novák,
• Melinda Nonn,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

• )-15b were formed as single products, without any regio- or stereoselectivity issues (Scheme 8). However, repeated N-halosuccinimide addition was necessary, and the yield of the bromofluorination reaction was still mediocre. The stereochemistry of the products (rac)-15a and (rac)-15b was determined by

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• David Van Craen Jenny Begall Johannes Grosskurth Leonard Himmel Oliver Linnenberg Elisabeth Isaak Markus Albrecht Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany 10.3762/bjoc.16.195 Abstract The stereoselectivity of a Diels–Alder reaction within the

• on the results of the stoichiometric reaction, a secondary amine-catalyzed nitro-Michael reaction is performed as well which afforded reasonable diastereoselectivities. Keywords: Diels–Alder reaction; enamine catalysis; hierarchical helicates; remote-control; stereoselectivity; Introduction Carbon

• –carbon (C–C) bond-forming reactions play a key role in organic chemistry. Hereby the stereoselectivity of the reaction is highly important due to the different behavior of stereoisomers in human metabolism [1][2]. Stereocontrol was achieved either via an auxiliary [3][4][5][6][7] or a catalyst [8], both

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• pyrrolidine byproduct. Using the Stork–Zhao conditions [23], the Nicolaou group performed an α-methyliodomethylenation of 24 to give 33 with a good stereoselectivity (Z:E ≈ 95:5, Scheme 4) [24][25]. After the hydrolysis of the dimethylaminal and the reaction of the resultant amine with phthalic anhydride, a

• with a poor stereoselectivity, however, a similar reduction of the diethyl acetal of 38, followed by an acetal hydrolysis gave the aldehyde 39 with a good stereocontrol (>10:1). It is not possible to make a direct comparison of the efficiency of these three routes as they do not lead to an identical

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

• improvement allowing to obtain 12a with up to 73% ee through the reaction with dihydroquinine benzyl ether (DHQ-Bn, Table 3, entry 12). Switching to quinidine (QD), dihydroquinidine (DHQD), and their derivatives allowed to alter the stereoselectivity of the process leading to the preferred formation of

• fluorinations with QD and DHQD led to the reversed stereoselectivity as compared to the reactions with Q and DHQ. For the benzylamine-derived substrates 8a–c benzyl ether derivatives of cinchona alkaloids favored the formation of the same enantiomer of 12 as their free alcohol counterparts (e.g., both Q-Bn and

Stereoselective Biginelli-like reaction catalyzed by a chiral phosphoric acid bearing two hydroxy groups

• Xiaoyun Hu,
• Jianxin Guo,
• Cui Wang,
• Rui Zhang and
• Victor Borovkov

Beilstein J. Org. Chem. 2020, 16, 1875–1880, doi:10.3762/bjoc.16.155

• indicated that the two free hydroxy groups in phosphoric acid 3 played a pivotal role in improving the stereoselectivity. A plausible activation model and reaction pathways of the stereogenic step in the phosphoric acid 3-catalyzed Biginelli-like reaction was proposed. This promising result prompted us to

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• -aldol reaction affording the final product (Scheme 34). This mechanism was experimentally supported by the beneficial effect of water and the observation of HF-loss by 19F NMR. The catalytic version of this process was also studied. The best results in terms of efficiency and stereoselectivity were

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• reactivity of 2-vinylpyrroles substituted by electron-withdrawing groups [34][35]. Interestingly, all the 2-vinylpyrroles, including the N-unsubstituted 16a,b or the N-substituted ones 8a and 8c–j, furnished a high endo stereoselectivity with dienophile 7c, except the N-substituted 2-acrylonitrile pyrrole 8b

• endo selectivity in the Diels–Alder cycloadditions. Since experimental and theoretical results have demonstrated that the nature of the C–H···π interaction mainly depends on the dispersion interactions [64][67][77], these are probably not only at the origin of the endo stereoselectivity of the present

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• isoxazolidines by means of dihydroxylation [9][10] and epoxidation [11][12] reactions. Regarding the stereochemistry, almost all of the realized additions proceed with an excellent trans stereoselectivity relative to the substituent at C-3, giving isoxazolidine-4,5-diols and isoxazolidinyl epoxides with a C-3/4

• the intended stereoselective reduction of cyclic ketones with the aim to obtain the 4-hydroxyisoxazolidines with a relative C-3/4-cis configuration. Whereas the initial attempts of the reduction of 9a with lithium borohydride resulted in a poor stereoselectivity (70:30 in favor of the desired cis

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• ]. Photodecarboxylations were also intensively investigated in a series of nonsteroidal anti-inflammatory drugs [22][23][24] such as ketoprofen [25][26][27][28][29][30][31][32][33][34], due to photoallergic responses initiated by photodecarboxylation of these drugs [35]. Stereoselectivity in photochemical reactions can be

• achieved by use of supramolecular chemistry [36][37]. For example, stereoselectivity has been reported for photochemical reactions taking place in the inclusion complexes with CD [38][39][40][41] or structurally modified CDs [42][43][44][45][46][47]. Since β-CD is often used in pharmaceutical applications

Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes

• Grzegorz Mlostoń,
• Mateusz Kowalczyk,
• André U. Augustin,
• Peter G. Jones and
• Daniel B. Werz

Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109

• the five-membered ring occurred regioselectively and the expected tetrahydrothiophene-3,3-carboxylates were the products. The studied reactions displayed an interesting stereoselectivity and, in the case of 2,5-diaryl-substituted products 9, both aryl groups were exclusively located at the opposite

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• endocyclic, high stereoselectivity was observed with the formation of trans-products (examples 106c and 108b). The oxidative cyclization of β,γ-unsaturated oximes 109 under the action of molecular oxygen and catalytic amounts of bis(5,5-dimethyl-1-(4-methylpiperazin-1-yl)hexane-1,2,4-trione)cobalt(II) (Co

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• establishes the syn approach of the C=C bonds. As a result, only the ε-isomer can be obtained and the stereoselectivity of the method is complete. As discussed previously, photocycloaddition products from the [2 + 2] reaction of the cisoid isomers of 3 were not observed, and we are unaware of the reasons for

• findings were also confirmed by analysis of the 13C NMR spectra. Conclusion The synthesis of cyclobutane 1,3-diaminotruxillic bis-amino acids has been achieved with full stereoselectivity (ε-isomer) starting from polyfunctional oxazolones 2 derived from the chromophore of the Kaede protein in three steps

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

• presence of Pd(OAc)2 as a catalyst. The corresponding β-fluoro derivatives 159a–v were obtained with high stereoselectivity using DCM and iPrCN as co-solvent (30:1 v/v). Interestingly reducing the Pd(OAc)2 concentration from 10 mol % to 6 mol % led to an improved yield of 73% for 159a, 159g, and 159t

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• (Scheme 3 (c)) leads to the expected 1,3-diene (Scheme 3 (d–f)). A particular advantage of the enyne metathesis is that the stereoselectivity can be readily controlled by the intramolecular vs the intermolecular process. Among the vast array of bioactive organic molecules already synthesized through enyne

Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol–carbene ligands

• Shohei Mimura,
• Sho Mizushima,
• Yohei Shimizu and
• Masaya Sawamura

Beilstein J. Org. Chem. 2020, 16, 537–543, doi:10.3762/bjoc.16.50

• plays crucial roles in both the catalytic activity and stereoselectivity [19][20][21]. Notably, these catalyst systems were also applicable for three-component coupling reactions using hydrosilanes as hydride reagents [17]. Based on this knowledge, we decided to investigate the effects of the phenol–NHC

Controlling alkyne reactivity by means of a copper-catalyzed radical reaction system for the synthesis of functionalized quaternary carbons

• Goki Hirata,
• Yu Yamane,
• Naoya Tsubaki,
• Reina Hara and
• Takashi Nishikata

Beilstein J. Org. Chem. 2020, 16, 502–508, doi:10.3762/bjoc.16.45

• stereoselectivity (Scheme 1, this work). Similarly, Zhu’s group has reported that the reaction of an alkyne and an α-bromocarbonyl compound furnishes a highly functionalized 1,3-enyne compound via ATRA followed by an alkynylation reaction [22], but both Pd and Cu are required as catalysts in that case. Our

• with good regio- and stereoselectivity. Results and Discussion In our preliminary research, we tried various Cu salts, including CuI, CuBr, CuCl, CuOAc, and CuOTf, and ligands, including PPh3, 1,10-phenanthroline (1,10-Phen), N,N,N',N'',N''-pentamethyldiethylenetriamine, and tris(2-pyridylmethyl)amine

• , in the reaction of phenylacetylene (1a) and α-bromoester 2a. From these experiments, CuBr and 1,10-Phen acted as a good catalyst system for obtaining 1,3-enyne 3a in 62% yield with good regio- and stereoselectivity (Table 1, entry 1). On the basis of this preliminary result, we also tried other

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• , providing a simplistic access to open-shell intermediates. These two synchronizing and rapidly flourishing areas of research in modern synthetic chemistry have recently been merged, and their association was found to be very effective in terms of chemo-, regio-, and stereoselectivity aspects. Therefore, we

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• enantiomers of the chiral ligand, either anti- or syn-1,3-deoxypropionate units were produced in good yields and excellent enantioselectivities (85–92% ee). Furthermore, an iterative procedure was also performed leading to all-syn or anti/syn-5,7,9-stereotriads, with high yields and stereoselectivity. This

• methodology was also tested on linear polyenic thioesters [9]. The challenging 1,8- and 1,10-products 21a/b were obtained, but the stereoselectivity dropped when the distance between the reacting olefin and the ester function was increased (1,8-ECA 72% ee; 1,10-ECA 45% ee). However, the regioselectivity (59

• performed with remarkable stereoselectivity (97–99%). Furthermore, this catalytic system was easily upscalable (up to 10 g), and the chiral catalyst could be recycled without any loss of efficiency. Unfortunately, although a wide range of Grignard reagents led to excellent results, PhMgBr provided low

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• reminiscent of the high stereoselectivity observed for [2 + 2] photodimerizations in organized media or in the solid state [37][38][39][40][41]. Considering the pronounced donor–acceptor interplay in 3b and 3c and the resulting strong dipole moment, it may be proposed that these compounds form dimeric

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• stereoselectivity of the acid-catalyzed rearrangement using enantiomerically enriched phosphine sulfides. Therefore, the chiral substrates (SP)-60, (SP)-65, (SP)-19, and (SP)-20 were prepared from dimethylphenylphosphine sulfide 4 using sparteine chemistry (Scheme 11). First, the enantioenriched alcohol (SP)-17

• , mesylate (SP)-60, and alkenylphosphine sulfide (SP)-65 were subjected to the reaction with Lewis-acidic AlCl3 (Scheme 12). Rearrangement of the tertiary alcohol (SP)-17 proceeded very efficiently, affording the corresponding product in high yield. Unfortunately, the stereoselectivity of the reaction

• . The transformation of alkenylphosphine sulfide (SP)-65 under similar reaction conditions led to the formation of β-mercaptoalkylphosphine oxide 53, albeit in low yield and with a complete lack of stereoselectivity. The results presented above show that, at least for mesylates, the sulfur atom

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• , De Meo and co-workers have reported the significant effect of O-substituents on atom C-7 on the reactivity of thiosialoside donors and on the anomeric stereoselectivity of chemical sialylations [21]. Thus, 2,7-anhydro-Neu5Ac can serve as a promising building block for the chemical synthesis of

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• supporting electrolyte. A slight improvement in the enantioselectivity (8.4% ee) was observed using 55b [55]. Kodama explained the reason of chiral induction in terms of ion pair interaction [56]. A further improvement in stereoselectivity was reported by Yadav, who added tetrabutylammonium trifluoroborate

• 66 (Scheme 26). Galvanostatic electrolysis of 66 in an undivided cell using a catalytic amount of 67 resulted in the corresponding lactones 68 in moderate yields and good stereoselectivities. The stereoselectivity was proposed to be controlled through the preferential formation of transition state A

• acetoacetates of Oppolzer’s sultam and Evans’ oxazolidin-2-ones afforded the best yields and diastereomeric ratios of addition products 170 relative to what was achieved with other chiral auxiliaries [98]. As a part of studies on the effects of chiral auxiliaries on the stereoselectivity in electrochemical

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• ). Moreover, the thermodynamically favored E-olefin was generated with high stereoselectivity in good yields. In 2012, two different groups [113][114] individually reported the direct trifluoromethylation of allylsilanes under very similar conditions. These processes furnished various branched cyclic and

• the same year, Loh’s group [132] used the same copper catalyst and Togni’s reagent to achieve the trifluoromethylation of enamides in good yields at room temperature (Scheme 72a). Meanwhile, this reaction exhibited excellent stereoselectivity towards the E-isomer. One year later, the same group [133

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• ] or diphenylfulvene [20][103][114][133][163][180]. In each instance, the endo stereochemistry of the cycloadduct is dominant [91][176][180], indicating that the fulvene substituents in the exocyclic C6 position are too distal to impact the stereoselectivity [76][229]. There are documented cases of

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• preexisting stereochemical elements influence the stereoselectivity of this reaction. To this end we investigated α-photooxygenation of chiral aldehydes with a stereocenter at the β-position (Scheme 1). In such a case, the outcome should depend on the relationships between the absolute configuration of the

• -photooxygenation of chiral aldehydes suggested that the stereocenter at the β-position has a strong impact on the stereoselectivity level. Model reaction Firstly, we tested three aldehydes 1–3 bearing substituents at the β-position. These substrates are easily accessible by photochemical means, according to the

• stereoselectivity was enforced by bulkier and electron-withdrawing groups as diarylprolinol silyl ether 18 (Table 1, entries 4 and 5). The absolute configuration of diastereoisomers formed was assigned using chiroptical spectroscopic methods (see section ‘Determination of the absolute configuration of the product