Solvent-free synthesis of enantioenriched β-silyl nitroalkanes under organocatalytic conditions

• Akhil K. Dubey and
• Raghunath Chowdhury

Beilstein J. Org. Chem. 2021, 17, 2642–2649, doi:10.3762/bjoc.17.177

• catalyst VIII led to ent-4 in 25% yield and 95% ee (Scheme 4). This observation confirmed that the presence of the β-silyl group in the enones played a key role in the high reactivity under the optimized reaction conditions. The stereochemistry of the silicon-substituted chiral center in compound ent-3k

Synthesis of new bile acid-fused tetrazoles using the Schmidt reaction

• Dušan Đ. Škorić,
• Olivera R. Klisurić,
• Dimitar S. Jakimov,
• Marija N. Sakač and
• János J. Csanádi

Beilstein J. Org. Chem. 2021, 17, 2611–2620, doi:10.3762/bjoc.17.174

• , TMSOTf proved to be the most efficient. High yields of the desired tetrazole compounds with no lactam byproduct were obtained. The molecular structure and stereochemistry of newly synthesized tetrazoles was established by detailed NMR analysis. For compounds 13 and 14, the structure was established by

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• example of the use of conjugation to drive an α-ketol rearrangement. This study elegantly illustrates the synthetic power of α-ketol rearrangements, whose suprafacial migration ensured that the α-ketol moiety present in the target product 31 was installed with correct stereochemistry. Taking inspiration

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• vinyl triflates 4a–c with a predominant formation of Z-isomers as product of an anti-addition of TfOH to the acetylene bond (Scheme 3). E/Z-Stereochemistry of compounds 4a–c was determined by H,F-NOESY correlation between vinyl proton (>C=CH–) and the CF3 group from the TfO substituent (see Supporting

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• the desired stereochemistry inversion at the C5’ carbon. Treatment with excess NaH furnished a terminal epoxide derivative which after the sequential treatment with benzyl bromide and reduction with LiAlH4 afforded alcohol 102 (81% yield from 95). The free secondary alcohol was then protected as TBS

• derivative in 80% yield. The TBS protecting group was removed under acidic conditions to give secondary alcohol 93 (85%). Afterwards, the 5,6-dihydro-α-pyrone functionality was constructed by applying a cross-metathesis protocol and the stereochemistry at C6’ was inverted with (E)-p-methoxycinnamic acid (17

• ) via a Mitsunobu esterification. The resulting product 106 contained all the correct stereochemistry, which after removal of the benzyl protection, provided the target molecule brevipolide M (13) as a colorless oil. Sabitha’s strategy to brevipolide M and N (13, 14) Following the previous success

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• selectivity of α-stereochemistry was primarily due to the strong directing effect of the neighboring benzyl ether group with the Hg(OAc)2. When cyclic mercuric halide 8 was treated with NaBH4 and oxygen (O2) in DMF oxidative demercuration takes place to give alcohol 10 in quantitative yield (Scheme 4). The

• (II)-salt-catalyzed rearrangement to produce 2,3-disubstituted-2,3-dihydropyranone derivatives 136. The stereochemistry of substituents at 2,3-positions of 2,3-dihydropyranone 136 was controlled by cis- and trans-configuration of the epoxide of starting materials (Scheme 40) [96]. Several unsaturated

• catalytic Hg(II)-salt-induced cyclization. Yamamoto and co-workers published the intermolecular cyclization of alkynyl-carboxylic acid 153 to produce 6-membered morpholine type ring compound 154 and compound 155 [103]. The stereochemistry of the chiral amino acid was not conserved in the cyclized product

Phenolic constituents from twigs of Aleurites fordii and their biological activities

• Kyoung Jin Park,
• Won Se Suh,
• Da Hye Yoon,
• Chung Sub Kim,
• Sun Yeou Kim and
• Kang Ro Lee

Beilstein J. Org. Chem. 2021, 17, 2329–2339, doi:10.3762/bjoc.17.151

• absolute configuration. The planar structure of 3 was further confirmed by analysis of 2D NMR data, including COSY, HSQC, and HMBC (Figure 2). The determination of the stereochemistry for the sugar unit of 3 was conducted following the same method as for compound 2. The structure of the aglycone 3a

• stereochemistry, but they showed quite different inhibition effects on NO production (IC50 55.0 μM, 2; IC50 > 500 μM, 5). The MTT cell viability test suggested that all the compounds had no cytotoxic effect on BV-2 cell survival at a concentration of 20 μM. Compounds 1–19 were also tested for their

Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• ) improved the reactivity somewhat but was detrimental to enantioselectivity (Table 1, entry 4), while changing the relative stereochemistry of the hydroxy substituent resulted in an inactive catalyst (8, entry 5 in Table 1). Likewise, catalysts such as 9 lacking a hydrogen-bonding substituent were not

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• . Deprotection followed by fluorination with FClO3 gave (R)- and (S)-28-3 in good yields. X-ray crystallography was used to determine the structure and confirm the absolute stereochemistry of (S)-28-3. The optically active reagents (R)- and (S)-28-3 were effective in the enantioselective fluorination of cyclic

Correction: Amine–borane complex-initiated SF₅Cl radical addition on alkenes and alkynes

• Audrey Gilbert,
• Pauline Langowski,
• Marine Delgado,
• Laurent Chabaud,
• Mathieu Pucheault and
• Jean-François Paquin

Beilstein J. Org. Chem. 2021, 17, 1725–1726, doi:10.3762/bjoc.17.120

• , France 10.3762/bjoc.17.120 Keywords: amine–borane complex; pentafluorosulfanyl chloride; pentafluorosulfanyl substituent; radical addition; radical initiation; The stereochemistry of some alkene products (2i–k) in Scheme 4 of the original publication was misattributed. The corrected structures are

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• basicity, the long reaction time of 20 hours may lead to an ion-pair species with 21 and hence erode the stereochemistry. To prove this idea, we performed the reaction with CH2Cl2 as the solvent in the presence of 5.0 equivalents of pyridine and 2.0 equivalents of TsCl. Under these conditions, the tosylate

• 21 was obtained with full retention of the expected stereochemistry (cis/trans =1:99) (see Supporting Information File 1 for details). The conversion of tosylate 21 to product 22 proceeded in a typical SN2 manner resulting in the expected inversion of the configuration. To unequivocally support the

Total synthesis of ent-pavettamine

• Memory Zimuwandeyi,
• Manuel A. Fernandes,
• Amanda L. Rousseau and
• Moira L. Bode

Beilstein J. Org. Chem. 2021, 17, 1440–1446, doi:10.3762/bjoc.17.99

• the current study, which aimed to establish a method for the synthesis of ent-pavettamine (2) so as to contribute towards a comprehensive structure–activity relationship study of pavettamine. With the absolute stereochemistry of pavettamine having been established previously [1], this study focused on

• that the new route doubled the overall yield to 16% for a similar number of steps. The specific optical rotation for 4 of +28.1° in acetone was comparable to that obtained previously [1]. Single crystal X-ray analysis of compound 4 (Figure 3), further confirmed the identity and stereochemistry of the

Analogs of the carotane antibiotic fulvoferruginin from submerged cultures of a Thai Marasmius sp.

• Birthe Sandargo,
• Leon Kaysan,
• Rémy B. Teponno,
• Christian Richter,
• Benjarong Thongbai,
• Frank Surup and
• Marc Stadler

Beilstein J. Org. Chem. 2021, 17, 1385–1391, doi:10.3762/bjoc.17.97

• (δH 4.95) and H3-13 (δH 0.99) indicating that they are on the same face of the molecule. These ROESY correlations are otherwise identical to those observed for fulvoferruginin (1). The relative stereochemistry at C-6 and C-10 was further confirmed through comparison with ROESY correlations of

• chirality method. Additionally, our recorded CD spectra (Figure S1 in Supporting Information File 1) of metabolites 3 and 4, are in close agreement with 1. As the metabolites 2–6 displayed analogous relative stereochemistry and optical rotations, we presume that the new compounds arise from the same

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• , the (S)-enantioselectivity could be reversed by inversion of stereochemistry at the terminal proline moiety of the supported peptide. Ötvös’ protocol highlights some of the key advantages of this immobilisation approach, i.e., improved reaction kinetics over batch (higher effective catalyst loading

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

• allylic bromides in the presence of zinc or indium metals is a well-known reaction [66][67]. It is possible to control and predict the stereochemistry of the addition to get the corresponding homoallylamine derivative with a high level of stereocontrol. The reaction of chiral imine 14 with an excess of

• consequence of the E stereochemistry of both the imine 14 and the enolate derived from bromoester 26 (Scheme 9). A two-step protocol carried out in a single synthetic operation was developed by Chen and Zhang to synthesize 3-substituted 2-chloroaziridines with relative cis configuration [71]. The reaction of

• hexamethyldisilazide was the base of choice to perform the deprotonation, and it must be added very slowly to the reaction mixture in order to suppress self-dimerization of the butenolide [72]. The structures as well as the absolute and relative stereochemistry of reaction products 30 and 31 were also unambiguously

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

• migratory insertion via TS1 (Scheme 13). The stereochemistry is controlled mainly by the hydrogen repulsion of the methylene group neighbouring the keto group of the enone with the t-Bu group of the ligand L9. Another interesting example for the application of this reaction in the preparation of precursors

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

• Ákos Bajtel,
• Mounir Raji,
• Matti Haukka,
• Ferenc Fülöp and
• Zsolt Szakonyi

Beilstein J. Org. Chem. 2021, 17, 983–990, doi:10.3762/bjoc.17.80

• , POB 35, 40351 Jyväskylä, Finland Stereochemistry Research Group of the Hungarian Academy of Sciences, H-6720 Szeged, Eötvös u. 6, Hungary, Interdisciplinary Centre of Natural Products, University of Szeged, Szeged, Hungary 10.3762/bjoc.17.80 Abstract A library of pinane-based 2-amino-1,3-diols was

• synthesised in a stereoselective manner. Isopinocarveol prepared from (−)-α-pinene was converted into condensed oxazolidin-2-one in two steps by carbamate formation followed by a stereoselective aminohydroxylation process. The relative stereochemistry of the pinane-fused oxazolidin-2-one was determined by 2D

• , two main synthetic strategies are used to prepare these analogues. One requires the insertion of the alcohol and amino groups in the α,β position with the correct stereochemistry [17][18][19][20]. The second strategy involves a bond formation between two chiral centers to produce the targeted 2-amino

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• (−)-blepharocalyxin D29 [45] and the macrolide leucascandrolide A [46]. In another type, the triflic acid-catalyzed Prins cyclization was used for the synthesis of 2,4,5,6-tetrasubstituted tetrahydropyran with complete control of stereochemistry, which is an important core of a variety of natural products, such as

• -stereochemistry in the major product. Asymmetric Prins cyclization Mullen and Gagné reported a first catalytic asymmetric Prins cyclization reaction between 2-allylphenol 292 and glyoxylate ester 293 using (R)-[(tolBINAP)Pt(NC6F5)2][SbF6]2 (294) as chiral catalyst [110]. An optimization study revealed that the

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• aluminum 2-methoxyethoxide, which attacks and inserts at the 2'-position, opening the ring and producing the nucleoside with the correct stereochemistry (Scheme 5) [117]. Conveniently, this 2'-O-MOE uridine can be converted to the cytidine derivative by 4-nitrophenylation, 3',5'-trimethylsilylation and

Simulating the enzymes of ganglioside biosynthesis with Glycologue

• Andrew G. McDonald and
• Gavin P. Davey

Beilstein J. Org. Chem. 2021, 17, 739–748, doi:10.3762/bjoc.17.64

• it is possible to infer that all of the enzymes of the model are all configuration-inverting, rather than configuration-retaining. This inversion of configuration refers to the stereochemistry of the anomeric carbon in the acceptor product, which has the opposite configuration to that of the donor

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• of diverse N-allylic α-(aminoxy)amides 9 from various epoxides 7 and a range of N-allylic α-silylamides 8. α-(Aminoxy)amides 9 serve well for the synthesis of polysubstituted γ-lactams 10 with moderate diastereoselectivities. The stereochemistry of the initial cyclization products can be however

Designed whole-cell-catalysis-assisted synthesis of 9,11-secosterols

• Marek Kõllo,
• Marje Kasari,
• Villu Kasari,
• Tõnis Pehk,
• Ivar Järving,
• Margus Lopp,
• Arvi Jõers and
• Tõnis Kanger

Beilstein J. Org. Chem. 2021, 17, 581–588, doi:10.3762/bjoc.17.52

• synthetic schemes starts with natural steroids, taking advantage of the appropriate stereochemistry of existing stereogenic centres [16][17][18][19][20]. However, the synthesis of target compounds is a multistep procedure, often including several protections and deprotections of functional groups. Our

Menthyl esterification allows chiral resolution for the synthesis of artificial glutamate analogs

• Kenji Morokuma,
• Shuntaro Tsukamoto,
• Kyosuke Mori,
• Kei Miyako,
• Ryuichi Sakai,
• Raku Irie and
• Masato Oikawa

Beilstein J. Org. Chem. 2021, 17, 540–550, doi:10.3762/bjoc.17.48

• * and 21 (see below). The PMB group of 20* and 20 was then independently removed by CAN at −10 °C to give 21* and 21 in 88% and 80% yield, respectively (Scheme 6). With 21* and 21, the stereochemistry was determined on the basis of the NOESY data in combination with the conformational analyses by

• , and the stereochemistry of 20 and 21 is 2R, as described in Figure 6, Scheme 5, and Scheme 6. The assignments were undoubtedly verified by the PGME amide analysis [22][23] (see the Supporting Information File 7). The stereochemical analyses carried out here and in our previous study [4] have been

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclic dienes

• Savva A. Ponomarev,
• Roman V. Larkovich,
• Alexander S. Aldoshin,
• Andrey A. Tabolin,
• Sema L. Ioffe,
• Jonathan Groß,
• Till Opatz and
• Valentine G. Nenajdenko

Beilstein J. Org. Chem. 2021, 17, 283–292, doi:10.3762/bjoc.17.27

• activation parameters. Furthermore, the synthetic utility of the cycloadducts obtained was demonstrated. Keywords: Diels–Alder reaction; fluorine; nitrostyrene; norbornene; stereochemistry; Introduction Organofluorine compounds play an exceptionally important role in various fields of science and

• , the ratio of endo/exo was 2:1. The stereochemistry of the products 2a–l can be unambiguously assigned using 1H NMR spectroscopy. According to the literature data [59] the dienophile-derived proton at C6 resonates at lower field in the exo-form than the corresponding proton of the endo-isomer. For