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

• formation of the expected N-benzylaminodiol either at room temperature or under reflux conditions, probably due to the strong steric hindrance of the bicyclic system and the hydroxymethyl group. The 1H NMR spectroscopic measurements in CDCl3 clearly showed that the crude product was a five-component

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• 1-O-methyl glucoside α-S9 as a glycosyl donor, we have demonstrated that methoxide can act as a mediocre leaving group in liquid SO2 (Scheme S1, Supporting Information File 1). Other limitations for the glycosylation with mannosyl fluoride α-1a include steric hindrance and the presence of a Lewis

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• yield from 69% to 84% over the conventional protocol as observed during the study. The explored mechanism in Scheme 16 indicates an in situ anti-azomethine ylide (A) generation (between isatin and primary amine) favored due to steric hindrance in syn-ylide. The crucial step determines the route via

• 115, could be only obtained. The regioisomer A being less stable due to steric hindrance between the amino and the aryl group rearranges to give desired product 115. The mechanism involved in the formation of intermediate B is similar to the mechanism proposed for amino-1,3,5-triazine ring

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

• additives at 50 °C and under irradiation with light (Scheme 32). The reaction is compatible with phenyl substituents with high steric hindrance, indicating that steric effects of the aryl moiety in the migrating styrenyl group do not play a major role. In 2018, You and colleagues [19] reported the discovery

Synthesis of β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

• Soumyaranjan Pati,
• Renata G. Almeida,
• Eufrânio N. da Silva Júnior and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2021, 17, 762–770, doi:10.3762/bjoc.17.66

• ) bearing pseudoaxially oriented OTs group suffers from only limited steric crowding (1,3-diaxial interaction). In the case of dimedone 2d, the two bulky methyl groups impart greater steric hindrance (1,3-diaxial interaction) to the incoming nucleophile in the event of pseudoaxial approach leading to

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

• Takashi Nishiyama,
• Erina Hamada,
• Daishi Ishii,
• Yuuto Kihara,
• Nanase Choshi,
• Natsumi Nakanishi,
• Mari Murakami,
• Kimiko Taninaka,
• Noriyuki Hatae and
• Tominari Choshi

Beilstein J. Org. Chem. 2021, 17, 730–736, doi:10.3762/bjoc.17.62

• reaction of 16a with CBr4, PPh3, and Et3N. Using the same procedure, carbodiimide 17b was then synthesized in 58% yield starting from aniline 14 via urea 16b. Then, the electrocyclization of 17b was attempted, but the cyclization did not proceed at all. As possible reason we considered a steric hindrance

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

Synthesis and physicochemical evaluation of fluorinated lipopeptide precursors of ligands for microbubble targeting

• Masayori Hagimori,
• Estefanía E. Mendoza-Ortega and
• Marie Pierre Krafft

Beilstein J. Org. Chem. 2021, 17, 511–518, doi:10.3762/bjoc.17.45

• blood circulation times by allowing them to evade immune detection. PEGs often play a key role in the design of the ligands as a spacer between the nanocarrier surface and the lipid. PEGs have, however, some shortcomings, such as a broad molecular weight distribution, large steric hindrance, and the

• proposed for the preparation of functional drug carriers for clinical applications [25][28][29]. In order to alleviate the steric hindrance effect of PEG chains, a novel spacer consisting of alternating serine–glycine sequences (SG)n was introduced between the ligand and lipid within the molecular

• step by washing. The human epidermal growth factor receptor-2 (HER2)-targeting KCCYSL peptide–(SG)n–lipids in which the (SG)n (n = 3, 5, 7) sequence was used as a spacer allowed the reduction of the steric hindrance when compared to the conventional PEG2000 spacer [28]. Liposomes containing these

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• the bisacetal precursor 4b bearing a 1,8-diphenylnaphthalene framework in 45% yield despite high steric hindrance (Scheme 4b). Then, [6]helicene (1b) was obtained in 92% yield via cycloaromatization in the presence of 15 mol % of TfOH. It was noted that the gram-scale synthesis for both [5]- and [6

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• change of the pH value from pH 7.0 to pH 5.0 leads to an addition of one hydroxy group. This means that the number of possible hydrogen bonds increases from four at pH 7.0 to five at pH 5.0. Yet, the added hydroxy group is in a position where steric hindrance can play a major role. Furthermore, Flavy and

Facile preparation and conversion of 4,4,4-trifluorobut-2-yn-1-ones to aromatic and heteroaromatic compounds

• Takashi Yamazaki,
• Yoh Nakajima,
• Minato Iida and
• Tomoko Kawasaki-Takasuka

Beilstein J. Org. Chem. 2021, 17, 132–138, doi:10.3762/bjoc.17.14

• slowdown of the reaction rate when tert-butylamine was employed, which was considered to be a reflection of the sensitivity of ynones 2 towards steric hindrance. Because appropriate conditions for the initial Michael addition reactions were thus determined, further conversion to the benzene derivative 4aa

Circularly polarized luminescent systems fabricated by Tröger's base derivatives through two different strategies

• Cheng Qian,
• Yuan Chen,
• Qian Zhao,
• Ming Cheng,
• Chen Lin,
• Juli Jiang and
• Leyong Wang

Beilstein J. Org. Chem. 2021, 17, 52–57, doi:10.3762/bjoc.17.6

• self-absorption and a wider stokes shift [17]. Further, the steric hindrance and highly rigidity could reduce non-radiative transition and restrict the internal rotation [18]. More importantly, in the TB structure, its bridged methylene groups of the diazocine chiral nitrogen atoms prevent the

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• conjugation. However, according to the energy profile, this observation does not have a reflection in the deprotonation step, which seems to be affected partially by the steric hindrance around the two hydrogen atoms, being clearly higher in Ha (a 2.2 kcal⋅mol−1 higher activation energy of TS10 than for TS8

Metal-free nucleophilic trifluoromethylselenolation via an iodide-mediated umpolung reactivity of trifluoromethylselenotoluenesulfonate

• Kevin Grollier,
• Alexis Taponard,
• Arnaud De Zordo-Banliat,
• Emmanuel Magnier and
• Thierry Billard

Beilstein J. Org. Chem. 2020, 16, 3032–3037, doi:10.3762/bjoc.16.252

• ) only 1 equivalent was required, maybe due to a higher reactivity. Furthermore, the reaction seems to be very sensitive to steric hindrance as illustrated by the low yield obtained for 3b. In contrast, in the aliphatic series, only low yields were observed (3m,n) except for the activated α-bromo

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• planes and the naphthalonitrile plane are 134.50° (C(3)–C(2)–C(12)–C(17)) and 46.80° (C(6)–C(1)–C(19)–C(24)), respectively. This means that the molecular structure of Me should involve torsion, which can be attributed to the steric hindrance of the two ortho-oriented phenyl rings. We can also observe

Regioselective synthesis of heterocyclic N-sulfonyl amidines from heteroaromatic thioamides and sulfonyl azides

• Vladimir Ilkin,
• Vera Berseneva,
• Tetyana Beryozkina,
• Tatiana Glukhareva,
• Lidia Dianova,
• Wim Dehaen,
• Eugenia Seliverstova and
• Vasiliy Bakulev

Beilstein J. Org. Chem. 2020, 16, 2937–2947, doi:10.3762/bjoc.16.243

• form can be explained by steric hindrance between the phenyl and the arylsulfonyl groups. Because of the observed evolution of nitrogen and sulfur in every reaction of heterocyclic thioamides and sulfonyl azides it is logic to propose the formation of a thiatriazole ring via [3 + 2] cycloaddition of

A novel and robust heterogeneous Cu catalyst using modified lignosulfonate as support for the synthesis of nitrogen-containing heterocycles

• Bingbing Lai,
• Meng Ye,
• Ping Liu,
• Minghao Li,
• Rongxian Bai and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2888–2902, doi:10.3762/bjoc.16.238

• were shown in Scheme 1. Aldehydes 2 with different functional groups on the benzene ring could react smoothly with compounds 1a and 3a, producing the corresponding 3,4-fused tricyclic indoles 4b–d with yields ranging from 46% to 64%. o-Anisaldehyde, with steric-hindrance effect, also reacted

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• binding constants, selectivities or optical responses should have been observed with the variation of the linker length. It may be concluded that the triazole ring, used as a synthetically convenient connection unit, imposes too much steric hindrance and restricted conformational flexibility in the

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2H-pyrans

• Viola Kolaříková,
• Markéta Rybáčková,
• Martin Svoboda and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2020, 16, 2757–2768, doi:10.3762/bjoc.16.226

• intermediate to undergo subsequent metathesis reactions leading to catalyst deactivation [23]. In both cases, the effect of ethene was especially productive for the Grubbs 1st generation precatalyst and is typically applied for terminal alkynes or alkynes with little steric hindrance of the triple bond. In

• these conditions a full or nearly complete conversion was observed with the exception of the silylated oxaenediyne 2f as was already reported for analogous published substrates [37]. Quite surprisingly, the necessity of a steric hindrance at the propargylic position in the RCEYM forming five-membered

• those using the G-I precatalyst and Mori conditions. The yields gradually improved with increasing steric hindrance of the triple bonds from oxaenediyne 2a (R = H) to 2d (R = Pr) for both precatalysts G-II and HG-II. This observation was in agreement with results reported in reference [23], which proved

Synthesis of purines and adenines containing the hexafluoroisopropyl group

• Viacheslav Petrov,
• Rebecca J. Dooley,
• Alexander A. Marchione,
• Elizabeth L. Diaz,
• Brittany S. Clem and
• William Marshall

Beilstein J. Org. Chem. 2020, 16, 2739–2748, doi:10.3762/bjoc.16.224

• , the enhanced imbalance in the population of the rotamers of 6a is notable and consistent with the amino moiety imposing a greater steric hindrance. The differences among the other compounds are more modest. The small entropy of activation is consistent with a simple rotation over a steric barrier

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• (Figure 2). The substituents COOH, SH, COO− and O− give rise to almost complete coordination of the cis isomer. In contrast to bimolecular coordination [12] the intramolecular coordination in the substituted cis isomers, obviously, does not follow a clear linear free energy relationship. Steric hindrance

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

• iodofluorination at reflux afforded only unreacted starting material. Since iodofluorination is usually more efficient than bromofluorination [19], the decreased yield of (rac)-20b compared to that of (rac)-20a is possibly caused by steric hindrance around the olefin bond, which affects the electrophilic attack of

• compared to bromo- and iodofluorination. However, since Cl+ is smaller and less sensitive to steric hindrance than Br+ or I+, the yield of chloro- and iodofluorination were comparable in this case. The stereochemistry of the above products was determined using NOESY measurements. The formation of two

• steric hindrance – and 33% unreacted starting material was recovered from the iodofluorination reaction mixture. In order to study the synthetic usefulness of the halofluorinated products, E2 hydrogen halide elimination was attempted. Since bromide and iodide are much better leaving groups than fluoride

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

• expected, the ortho-substituent on the phenyl ring of the boronic acid impeded N1-arylation by steric hindrance. However, the methoxy and methyl groups at the ortho position did not prevent the formation of the corresponding products 3o and 3p, which were isolated in moderate yields of 52 and 35

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• photodissociable ligands. These ligands coordinate in their trans form and decoordinate in the cis configuration driven by steric hindrance [14][34][35]. Basicity and nucleophilicity switching of the 4-(N,N-dimethylamino)pyridine “record player” molecule 1. Composition of the different states of porphyrin 1 (1 mM

How and why plants and human N-glycans are different: Insight from molecular dynamics into the “glycoblocks” architecture of complex carbohydrates

• Carl A. Fogarty,
• Aoife M. Harbison,
• Amy R. Dugdale and
• Elisa Fadda

Beilstein J. Org. Chem. 2020, 16, 2046–2056, doi:10.3762/bjoc.16.171

• the reader. As shown in Tables S1 and S2 in Supporting Information File 1, the equilibrium of the (1-3) arm is not affected by core α(1-3)-Fuc. β(1-2) xylose in plant N-glycans: Because the β(1-2)-Xyl sits in front of the two arms, it greatly affects their dynamics. Because of steric hindrance, the (1

• chitobiose core in a ‘front fold’ either, because of steric hindrance. Also, similarly to the α(1-3) fucosylated glycans, the stability of the open structure is slightly increased when the arm is further functionalized with terminal β(1-3)-Gal, see Table S4 in Supporting Information File 1. As an additional

• completely absent in mammalian N-glycans. Within the context of plant-type N-glycans, which have a terminal β(1-3)-Gal, rather than β(1-4)-Gal, both β(1-2)-Xyl and α(1-3)-Fuc contribute independently in promoting an outstretched (open) conformation of the (1-6) arm because of steric hindrance of the xylose