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

Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• 351-0198, Japan Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 10.3762/bjoc.15.184 Abstract We previously showed that the regio- and stereoselectivity in terpene-forming reactions are determined by the conformations of the carbocation

• means high mobility, yellow means moderate mobility, and blue means static. TS: transition state. The regio- and stereoselectivity in quiannulatene and sesterfisherol biosynthesis are determined by the initial conformation of GFPP. Reaction mechanism of quiannulatene biosynthesis. GFPP: geranylfarnesyl

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• subjected to silica gel chromatography. Compound 4 was used to determine the stereoselectivity of the cycloaddition step as well as for oxidation. Oxidation of the 2-isoxazoline 4 with Jones’ reagent gave a complicated mixture, in which the desired carboxylic acid was not observed (Scheme 2). The stepwise

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• elucidating the origin of the stereoselectivity in the synthesis of 6R. The 1H spectrum of 4R is generally similar to that of 6R and strong NOE cross peaks between the triazole and CB[6], and also Ha of the anthracene and CB[6] protons were observed (Figure S10 in Supporting Information File 1), confirming

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

• of chemical and configurational stability was achieved by introducing N,N-dibenzylserinals 4 [10]. Another important strategy of asymmetric synthesis relies on chiral auxiliaries, i.e., a specially selected homochiral part of a starting material governing the stereoselectivity of subsequent reactions

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

• Anthony Choi,
• Rebecca M. Morley and
• Iain Coldham

Beilstein J. Org. Chem. 2019, 15, 1480–1484, doi:10.3762/bjoc.15.149

• types of products. Conclusion In conclusion, we have found that carboxylic ester and amide-stabilised anions derived from quinolinium salts react with arylidenemalononitriles and N-methylmaleimide to give adducts in good yields and with very high stereoselectivity (single isomer products were isolated

Fluorine-containing substituents: metabolism of the α,α-difluoroethyl thioether motif

• Andrea Rodil,
• Alexandra M. Z. Slawin,
• Nawaf Al-Maharik,
• Ren Tomita and
• David O’Hagan

Beilstein J. Org. Chem. 2019, 15, 1441–1447, doi:10.3762/bjoc.15.144

• with very similar outcomes. In order to explore the stereoselectivity of this sulfoxidation, sulfoxide 11 isolated from the C. elegans incubation was analysed by chiral HPLC (IC column, solvent: 5% isopropanol in hexane; 1 mL/min). This was compared to a racemic reference sample of 11 prepared by

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• the reaction. Indeed, the bulkier the boron substituent is, the more efficient is the process. Therefore, the substitution at the boron plays a key role, most probably at the boron rearrangement step (see below). Stereoselectivity, scope and limitations Next, the stereoselectivity of this

• existence of at least one concerted step during the reaction mechanism. This step most probably corresponds to the group transfer in organoboron derivatives, as the stereoselectivity of such transfer has been demonstrated [32][33]. Regarding the oxiranyllithium stereochemical integrity and stability, it has

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

• 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

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• the observed stereoselectivity are provided in Supporting Information File 1, Figure S3. Conclusion In summary, we have introduced a new motif of chiral weakly coordinating Fe(III)-based bisphosphate anion for high performance asymmetric carbocation Lewis acid catalysis. The introduction of a metal

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• intermediate was far away from the chiral steroidal nucleus. A better stereoselectivity was reported by Bruttomesso et al. in their work on the Ugi four-component reaction (Ugi-4CR) with a steroidal aldehyde, in which the carbonyl group was directly linked at the steroidal framework [16]. As shown in Scheme 2

• to be conducted at reflux to obtain a good yield of Ugi-derived steroids, albeit the procedure generated a pair of diastereomers (epimeric at C-5) in almost equal amount. The stereoselectivity of the intramolecular MCR increased when a bulky isonitrile was used, e.g., diethyl phosphonate isocyanide

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• produced by means of an initial Ugi reaction followed by an acid-catalyzed polymerization. They catalytic polymers were screened in the heterogeneous catalytic Michael addition in batch, proving that catalyst 3 is more effective and provides better stereoselectivity. A continuous-flow organocatalytic

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• by slow warming to ≈−10 °C before work-up. Finally, the reaction displayed remarkable stereoselectivity, in that the electrophile was introduced on ostensibly the more hindered face of the enolate (that is, cis (“contrasteric”) [24] to the unenolised ester group). The former observation was

• rationalisation of stereoselectivity [17][18][19]. Tartrate alkylation with a non-activated alkyl iodide. Alkylated tartrate to diazoester sequence. TES protection approach to the squalestatin core. Tartrate acetonide methylation. Tartrate alkylation with various alkyl halides. Rationalisation of dialkylation

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

• -terminal CRD), -7, -8C, -8N, -9C, and -9N. Results and Discussion Chemistry The synthesis starts from the known enol ethers 2, 4, and 6 prepared using published methods [25][26]. Hydroborations of enol ethers have been known to give good to excellent regio- and stereoselectivity and are thus a possible

• analog 6 to β-7 in high yield and with excellent stereoselectivity [31]. In none of the reaction conditions 1-methyl glycopyranoside side products were formed (Scheme 1). Continuing the synthesis towards (aryltriazolyl)methyl galactopyranosyl derivatives, the 2-deoxygalactoheptulose 3 was mesylated with

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• stereoselectivity of the reaction was not controlled by relative thermodynamic stability of the diastereomers. The major isomer of 3c, which contained a sterically less demanding Ph group at the R1 position (cf. Table 1), did not isomerize at room temperature for 1 year. However, heating a solution of this compound

• in MeCN at 80 °C for 4 h resulted in a mixture of diastereomers in a ratio of 3:1. These results suggest that the sterically demanding substituents at R1 and R2 positions (cf. Table 1) are critical to ensure good stereoselectivity during the product formation and to prevent isomerization after the

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

• (or amination) sequence on achiral nonfunctionalized cyclopropenes provided the desired cyclopropanol (and cyclopropylamine) derivatives in excellent diastereo- and enantiomeric excesses. Keywords: carbocupration; cyclopropanol; cyclopropene; regioselectivity; stereoselectivity; Introduction The

• usually proceeds through single-electron transfer to dioxygen, leading to either a loss of stereoselectivity, degradation of the organocopper or to the formation of dimer as major products [71]. Therefore, it was clear that a different approach for the oxidation process was needed. Oxenoid, possessing the

Influence of per-O-sulfation upon the conformational behaviour of common furanosides

• Alexey G. Gerbst,
• Vadim B. Krylov,
• Dmitry A. Argunov,
• Maksim I. Petruk,
• Arsenii S. Solovev,
• Andrey S. Dmitrenok and
• Nikolay E. Nifantiev

Beilstein J. Org. Chem. 2019, 15, 685–694, doi:10.3762/bjoc.15.63

• pyranosides [10][11] and thus the effects of substitution in them are more complex. The conformational effects underlay the striking stereoselectivity in the glycosylation reaction by furanosyl donors [12]. Conformational analysis of furanosides includes both conformation of the furanoside ring and