Enhanced reactivity of Li⁺@C₆₀ toward thermal [2 + 2] cycloaddition by encapsulated Li⁺ Lewis acid

• Hiroshi Ueno,
• Yu Yamazaki,
• Hiroshi Okada,
• Fuminori Misaizu,
• Ken Kokubo and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2024, 20, 653–660, doi:10.3762/bjoc.20.58

• likely due to the steric effect caused by the methyl group directly connected to the alkenyl C=C bond in reactant 1. After optimizing the reaction conditions, compounds 5a and 5b were isolated in 71% and 53% yields, respectively. Importantly, the generation of multiadducts in the thermal [2 + 2

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• can decompose to produce a stoichiometric pair of the primary initiating radical and a nitroxide radical, thus combining the roles of a conventional initiator and a control agent. The mechanism is shown in Scheme 4 [35]. Due to the steric effect of TEMPO, the dissociation rate constant, kd, of the

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• exo ratio was either related to the electron density of the alkene or the steric effect of a substituent. The tether lengths could affect the cyclization. For example, the two-carbon-tethered substrate completely showed endo selectivity, while the four-carbon-tethered substrate exclusively led to

• the product 162 and regenerated HX. In path II, I reacted with nucleophile 161 to produce a byproduct, phthalimide, and HX (Scheme 70). The coupling reaction was influenced by nucleophilic properties and the steric effect of the nucleophile reagents. In the same year, the treatment of amines with N

Selective construction of dispiro[indoline-3,2'-quinoline-3',3''-indoline] and dispiro[indoline-3,2'-pyrrole-3',3''-indoline] via three-component reaction

• Ziying Xiao,
• Fengshun Xu,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 1234–1242, doi:10.3762/bjoc.19.91

• indicated that only one diastereoisomer was predominately produced in the reaction, while the other possible diastereomers were not detected. This result shows that this reaction has a high diastereoselectivity due to the large steric effect of two oxindole scaffolds and the thermodynamically controlling

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• bonding occurring between the Lewis basic ether and a σ-hole on the electropositive iodine (Scheme 14, inset). These results suggest that with iodonium ylides, ortho-substituents impose an electronic effect (compare 62a vs 62b and 62b vs 62c), contrary to the steric effect observed for radiofluorination

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• . By the steric effect of the existing tert-butyl groups in precursor 90, another two extended carbo[5]helicenes were formed in the final Scholl reaction of precursor 90 except for the centred carbo[7]helicene in the final structure 91. Initial analysis of the final products by chiral stationary phase

Ferrocenoyl-adenines: substituent effects on regioselective acylation

• Mateja Toma,
• Gabrijel Zubčić,
• Jasmina Lapić,
• Senka Djaković,
• Davor Šakić and
• Valerije Vrček

Beilstein J. Org. Chem. 2022, 18, 1270–1277, doi:10.3762/bjoc.18.133

• the acylation of purines from a regioselective to a regiospecific mode. Keywords: DFT; ferrocene; nucleophilicity; purine; steric effect; Introduction Nucleosides in which the sugar part is replaced with an organometallic moiety have attracted remarkable interest [1][2][3]. One important class are

• group. In case when the steric effect is negligible (e.g., H atom at the C6-position), the N9-isomer is a minor product (less than 30%), and the acylation of the N7 position is strongly favored. In the parent purine, therefore, the nucleophilic attack is mostly controlled by electronic effects, i.e

• -weighted parameters, which are conformationally dependent, and thus may define the steric effect for any conceivable substituent. They are multidimensional parameters, that is, they describe steric bulk along different principal axes, hence, the effects of unsymmetrical substituents are better described

Radical cation Diels–Alder reactions of arylidene cycloalkanes

• Kaii Nakayama,
• Hidehiro Kamiya and
• Yohei Okada

Beilstein J. Org. Chem. 2022, 18, 1100–1106, doi:10.3762/bjoc.18.112

• at the β-position had a significant impact on the reaction. In general, tertiary radicals (or cations) are more stable than secondary ones and therefore, the additional methyl group seems to have a strong steric effect (Figure 3). If so, tying up the two methyl groups as a cyclopropane ring may

Bioinspired tetraamino-bisthiourea chiral macrocycles in catalyzing decarboxylative Mannich reactions

• Hao Guo,
• Yu-Fei Ao,
• De-Xian Wang and
• Qi-Qiang Wang

Beilstein J. Org. Chem. 2022, 18, 486–496, doi:10.3762/bjoc.18.51

• linking components to afford Lewis base sites and also for introduction of chirality. Different alkyl substituents including methyl, n-propyl, isopropyl, and 3-pentyl were incorporated in order to tune the size and steric effect of the macrocyclic cavity and thus to enable diverse cavity environments

• disrupted by 4-substitution, and only trace conversion was observed for the 4-chloro or 4-bromo-substituted substrate (8o,s). This was probably caused by a steric effect as the 4-substituent is close to the imine reactive site and accordingly blocked it toward activation and nucleophilic attack

Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• the 1,4-position of 1. On the other hand, the double bond of 2 hardly interacted with the 9,10-position of 1, because of the steric effect induced by the cage host A. This methodology was also compatible with several other anthracene substrates with different substituents at the 9-position. But when

Ready access to 7,8-dihydroindolo[2,3-d][1]benzazepine-6(5H)-one scaffold and analogues via early-stage Fischer ring-closure reaction

• Irina Kuznetcova,
• Felix Bacher,
• Daniel Vegh,
• Hsiang-Yu Chuang and
• Vladimir B. Arion

Beilstein J. Org. Chem. 2022, 18, 143–151, doi:10.3762/bjoc.18.15

• led exclusively to the desired isomer 5 with the nitrophenyl group in position 3, most likely due to the steric effect. Then, the nitro group in 5 was reduced by hydrogenation under 4 bar using Pd/C as catalyst to yield the desired amine 6 in 78% yield. Subsequently, the desired chloroacetyl

Efficient and regioselective synthesis of dihydroxy-substituted 2-aminocyclooctane-1-carboxylic acid and its bicyclic derivatives

• İlknur Polat,
• Selçuk Eşsiz,
• Uğur Bozkaya and
• Emine Salamci

Beilstein J. Org. Chem. 2022, 18, 77–85, doi:10.3762/bjoc.18.7

• diol 5 as a single isomer in 91% yield. We assume that the trans selectivity of hydroxylation in ester 4 is due to the steric effect of the presence of the bulky Boc group. The structure of 5 was determined with the help of 1D (1H and 13C) and 2D (COSY and HMQC) NMR spectra. The diagonal peak at 4.10

Regioselective N-alkylation of the 1H-indazole scaffold; ring substituent and N-alkylating reagent effects on regioisomeric distribution

• Ryan M. Alam and
• John J. Keating

Beilstein J. Org. Chem. 2021, 17, 1939–1951, doi:10.3762/bjoc.17.127

• augmented by the steric effect that the C-3 substituent enforces. The high degree of N-1 regioselectivity obtained for indazoles bearing bulky substituents at the C-3 position that are not capable of engaging in tight ion pair formation, such as 14 and 15, further highlights the influence of steric effects

Changed reactivity of secondary hydroxy groups in C8-modified adenosine – lessons learned from silylation

• Jennifer Frommer and
• Sabine Müller

Beilstein J. Org. Chem. 2020, 16, 2854–2861, doi:10.3762/bjoc.16.234

• of the linker L at C8 in derivative 7 changes the J1’-2’ coupling constant only slightly (4.8 Hz J1’-2’), however, brings in a strong steric effect and most likely induces a preferential syn-conformation of the nucleobase relative to the sugar residue. These effects together can be accounted for the

Efficient [(NHC)Au(NTf₂)]-catalyzed hydrohydrazidation of terminal and internal alkynes

• Maximillian Heidrich and
• Herbert Plenio

Beilstein J. Org. Chem. 2020, 16, 2080–2086, doi:10.3762/bjoc.16.175

• conversion to 6 and provided isolated yields in excess of 90% using as little as 0.1–0.2 mol % of complex 1. Just like in related reactions, the nucleophile exclusively added to the β-carbon of the triple bond. A single substituent in the ortho-position of the alkyne did not exert a strong steric effect

Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines

• Ksenia I. Kaskevich,
• Anastasia A. Babushkina,
• Vladislav V. Gurzhiy,
• Dmitrij M. Egorov,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2020, 16, 1947–1954, doi:10.3762/bjoc.16.161

• thiazolo[3,2-a]-5-oxopyrimidines 3a–f in good yields (Scheme 6). Likely, in this case the attack by the N3 atom was more favorable than by the N1 atom due to the steric effect of the substituent in position 6. The reactions proceeded under mild conditions within 3–5 hours. Anhydrous K2CO3 was used as a

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• conformation. An electron-withdrawing substituent tends to adopt an axial position due to an orbital effect called the gauche-effect (stereoelectronic effect) [67][68]. Conversely, a bulky substituent adopts an equatorial position (steric effect) [69][70]. At the same time, there has been no evidence that a

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• both (R) and (S)-isomers, and 1,1-diphenylethene (216c) under UV irradiation. As the products spirothietane-pyrrolidinones 320 were obtained in 65–89% yield. The diastereoselectivity was controlled by the steric effect of the ortho-substituents on the phenyl ring [88] (Scheme 59). The intermolecular

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

• and benzyl, were tolerated (46i and 46j). The yield of the C–O cross-coupling products 46 increases with the rise in the stability of the corresponding oxime radicals. For example, in the row 46f–h the yield becomes higher with the increase of the steric effect of the alkyl substituents attached to

• relatively low yield of product 138f was explained by the steric effect of the ortho-methyl substituent in amide 137. In most cases, N-aryl-N-methylmethacrylamides were used for this cyclization to obtain oxindoles (products 138a–g) except for one example where a homologous amide was used to obtain six

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• resistance than geminal ethyl groups can. Thus, estimation of the steric effect of neighbouring substituents cannot account for the high reduction resistance of 1. Presumably, the symmetric structure with bulky substituents at positions 3 and 4 is an important factor for nitroxide stability. Due to the

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

• -CD was obtained could also be attributed to a similar steric effect if the CB[6] and γ-CD are in close proximity, which is also consistent with the proposed structure of 4R. Again, the γ-CD is proposed to face the CB[6] with its primary face due to the better size match and stronger interactions. In

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• ligand, and that was to focus on substituents on the α-carbon of the ligand. To our knowledge, there are no reports on investigations of electronic and/or steric effect(s) of pyridinyl substituents on the chelation efficiency of pyridinyl alcoholato ligands, and subsequently its metathesis activity

• electron-donation by the methyl group cannot significantly influence the electron density on the pyridine nitrogen. There is also no steric effect that would interfere with the Ru–N bond strength. The strengthening effect on the Ru–N chelation would, therefore, possibly be low compared to the other

• to hemilability than 6 and exhibits higher activity. Therefore, for 4-Me- and 5-Me-subtstituted precatalysts, only the inductive electron-donation effect of the methyl group is the reason for the increased stability. In the 3-Me- and 3-OMe-substituted precatalysts, however, the steric effect and

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• amines, and silyl alkynes in the presence of CoCp*(CO)I2 catalyst gave uncommon branched-selective products 16 in good yields with reasonable selectivity (Scheme 12) [56]. DFT calculations indicated that the regioselectivity of silyl alkynes was controlled by its steric effect in the protonolysis step

• , whereas the IPr·HCl ligand provided tetrahydropyridoindoles 31 in reasonable regioselectivity (Scheme 22) [70]. Remarkably, the regioselectivity of the reaction is not only controlled by the steric effect of NHC ligand, but also depends on the olefin tether in 29. Recently, Petit and co-workers also

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases

• Maroš Bella,
• Sergej Šesták,
• Ján Moncoľ,
• Miroslav Koóš and
• Monika Poláková

Beilstein J. Org. Chem. 2018, 14, 2156–2162, doi:10.3762/bjoc.14.189

• was decreasing with increasing size of this functional group, suggesting a certain role of steric effect. An even smaller effect was found for 4-halogenation of the N-benzyl substituent, arguing against a steric or electron effect at this position of the phenyl ring. Nevertheless, the synthesis of