Tetraphenylethylene-embedded pillar[5]arene-based orthogonal self-assembly for efficient photocatalysis in water

• Zhihang Bai,
• Krishnasamy Velmurugan,
• Xueqi Tian,
• Minzan Zuo,
• Kaiya Wang and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2022, 18, 429–437, doi:10.3762/bjoc.18.45

• Supporting Information File 1). When 1 equiv of EsY was added into the m-TPEWP5G solution, the resonance signals of EsY were shifted to upfield regions, which was caused by steric effects and electrostatic interactions between the quaternary ammonium groups containing m-TPEWP5 and the negatively charged EsY

Four bioactive new steroids from the soft coral Lobophytum pauciflorum collected in South China Sea

• Di Zhang,
• Zhe Wang,
• Xiao Han,
• Xiao-Lei Li,
• Zhong-Yu Lu,
• Bei-Bei Dou,
• Wen-Ze Zhang,
• Xu-Li Tang,
• Ping-Lin Li and
• Guo-Qiang Li

Beilstein J. Org. Chem. 2022, 18, 374–380, doi:10.3762/bjoc.18.42

• oxygenated sp3 secondary carbon (δC 76.3) and one oxygenated sp3 quaternary carbon (δC 74.2). As two of the six degrees of unsaturation were occupied by the double bond and carbonyl group, the remaining four unsaturations of 1 corresponded to a tetracyclic skeleton. The 1H,1H-COSY experiment (Figure 2

Amamistatins isolated from Nocardia altamirensis

• Till Steinmetz,
• Wolf Hiller and
• Markus Nett

Beilstein J. Org. Chem. 2022, 18, 360–367, doi:10.3762/bjoc.18.40

• the basis of 2D NMR data. In the HMBC spectrum, the singlet methyl protons H3-17 and H3-18 show correlations to C-7, a quaternary carbon at 47.4 ppm (C-8), and an oxymethine carbon at 80.3 ppm (C-9). COSY and HMBC data established the alkyl chain from CH-9 to CH3-16. A correlation between H-9 and C-19

Unexpected chiral vicinal tetrasubstituted diamines via borylcopper-mediated homocoupling of isatin imines

• Marco Manenti,
• Leonardo Lo Presti,
• Giorgio Molteni and
• Alessandra Silvani

Beilstein J. Org. Chem. 2022, 18, 303–308, doi:10.3762/bjoc.18.34

• products we disclosed the efficient homocoupling of oxindole-based N-tert-butanesulfinyl imines, with the generation of chiral, quaternary 1,2-diamines in a mild and completely stereoselective way. The obtained 3,3′-bisoxindole derivatives were fully characterized by NMR and single-crystal X-ray

• because they can serve as key synthetic intermediates in the construction of complex natural products [17][18][19][20][21][22][23]. Particularly challenging is the placement of the two C3/C3’ contiguous quaternary stereogenic centers, just as they are found in various alkaloids, such as those belonging to

• corresponding quaternary 1,2-diamines were obtained. Instead, the presence of a substituent at the C4 position (4-Cl, 2g) hinders the course of the reaction, likely due to its spatial proximity with the reaction center, and no homocoupling could be observed. In order to rationalize the formation of bisoxindole

Organocatalytic asymmetric nitroso aldol reaction of α-substituted malonamates

• Ekta Gupta,
• Narendra Kumar Vaishanv,
• Sandeep Kumar,
• Raja Krishnan Purshottam,
• Ruchir Kant and
• Kishor Mohanan

Beilstein J. Org. Chem. 2022, 18, 217–224, doi:10.3762/bjoc.18.25

• with nitrosoarene which provides facile access to chiral hydroxyamino malonamates having a quaternary carbon stereocenter (Scheme 1). Results and Discussion Initially, we chose the Takemoto catalyst to promote the model reaction between methyl N-bromophenyl-α-methylmalonamate (1a) and nitrosobenzene

Glycosylated coumarins, flavonoids, lignans and phenylpropanoids from Wikstroemia nutans and their biological activities

• Meifang Wu,
• Xiangdong Su,
• Yichuang Wu,
• Yuanjing Luo,
• Ying Guo and
• Yongbo Xue

Beilstein J. Org. Chem. 2022, 18, 200–207, doi:10.3762/bjoc.18.23

• 161.1), seven sp2 quaternary carbons (including five O-bearing aromatic carbons at δC 162.2, 156.4, 154.0, 153.5, and 141.5; and two aromatic carbons at δC 114.7 and 114.3), nine methine groups (δC 115.4, 143.7, 121.4, 106.5, 115.0, 144.2, 130.3, 114.2, 105.3), nine oxygenated methine carbon atoms (δC

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• . The 1H,13C-HMBC spectrum of compound 4a revealed that the methylene protons from the azetidine moiety and the 1,2-oxazole methine proton H-3, exhibited long-range correlations with quaternary carbon C-5 (Figure 2c). The aforementioned protonated carbons C-3 and C-3’ showed correlations in the 1,1

• -ADEQUATE spectrum thus allowing to assign a neighboring quaternary carbons C-4 (δ 109.9 ppm) and C-5 (δ 175.4 ppm), H–C(3)–C(4) and H–C(3’)–C(5), respectively. The 1H,15N-HMBC experiment revealed an expected long-range correlation between the 1,2-oxazole methine H-3 proton (δ 8.50 ppm) and nitrogen N-2

Unsaturated fatty acids and a prenylated tryptophan derivative from a rare actinomycete of the genus Couchioplanes

• Shun Saito,
• Kanji Indo,
• Naoya Oku,
• Hisayuki Komaki,
• Masashi Kawasaki and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2939–2949, doi:10.3762/bjoc.17.203

• former two fragments were intervened by an sp2 quaternary carbon (C-4) substituted by an allylic methyl group (H-11) based on HMBC correlations from H-11 to C-3, C-4, and C-5. Another intervention by a methylene unit (C-8) to connect the second and third fragments was supported by HMBC correlations from

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• regio- and stereoselective γ-addition reaction of isoxazol-5(4H)-ones 103 to β,γ-alkynyl-α-imino esters 102 for the synthesis of axially chiral tetrasubstituted α-amino allenoates 104 containing an adjacent quaternary carbon stereocenter and an axially chiral tetrasubstituted allene scaffold [104

• phosphoric acid catalysis, we developed a highly regio-, diastereo-, and enantioselective dearomatization reaction of 1-substituted 2-naphthols 115 and β,γ-alkynyl-α-imino esters 100. The highly functionalized naphthalenone derivatives 116 with an allene moiety, exhibiting both a quaternary stereocenter and

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• cinchona alkaloid-derived quaternary ammonium salts (cat. 55) as the phase-transfer catalyst. The products were obtained in high yields (53–93%) with high enantioselectivities (40–76% ee) (Table 12) [46]. Lebrun et al. developed a new method to synthesize optically active isoindolinones via asymmetric

• aza-Michael/alkylation reaction catalyzed by cinchona alkaloid-derived quaternary ammonium salts. Asymmetric aza-Michael synthesis of isoindolinones. Asymmetric aza-Michael addition reaction catalysed by chiral bifunctional thiourea. Enantioselective 1,6-aza-Michael addition of isoxazolin-5-ones to p

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

• Martin Kamlar,
• Robert Reiberger,
• Martin Nigríni,
• Ivana Císařová and
• Jan Veselý

Beilstein J. Org. Chem. 2021, 17, 2433–2440, doi:10.3762/bjoc.17.160

• from preformed imines instead of aldehydes catalyzed by BINOL-phosphoric acid [17]. The corresponding aminals were prepared with a wide range of substitutions using aromatic, α,β-unsaturated, or aliphatic imines. Apart from chiral phosphoric acids, chiral quaternary ammonium salts were successfully

Isolation and characterization of new phenolic siderophores with antimicrobial properties from Pseudomonas sp. UIAU-6B

• Emmanuel T. Oluwabusola,
• Olusoji O. Adebisi,
• Fernando Reyes,
• Kojo S. Acquah,
• Mercedes De La Cruz,
• Larry L. Mweetwa,
• Joy E. Rajakulendran,
• Digby F. Warner,
• Deng Hai,
• Rainer Ebel and
• Marcel Jaspars

Beilstein J. Org. Chem. 2021, 17, 2390–2398, doi:10.3762/bjoc.17.156

• that revealed a molecular ion at m/z 237.0874 (calcd for C11H13N2O4−, 237.0880). A thorough analysis of 1H and 2D NMR data (see Table 1 and Supporting Information File 1) showed four aromatic methines, two aliphatic methines, one methyl, and four quaternary carbons signals at δC 162.9 (C-1), 113.2 (C-6

• acid unit, confirmed by long-range correlations observed in the HMBC spectrum from H-2, H-4 to C-6 (δC 113.2), and H-5 to the quaternary carbon C-7 (δC 170.0). On the other hand, the COSY spectrum confirmed the presence of a CH3–CH–CH spin system (H3-12, H-11, and H-9) reminiscent of a threonine unit

• carboxamide C-10 (δC 172.9) and the quaternary carbon C-16 (δC 140.2), between H2-15 and H-18/20 to the quaternary carbon C-16, and a strong correlation from H-15 and H-19 to C-17/20 (δC 129.9). The new oxazoline derivative 5 was named pseudomonbactin B. The absolute configuration of the threonine residue in

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

• for the synthesis of 1,4-dihydroquinoline 129 possessing a quaternary carbon center from 128 [93]. The reaction was reported via a seven-membered bicyclic hemiaminal as mentioned in the mechanism. This catalytic rearrangement protocol was successfully applied for the construction of complex carbon

• Yamamoto et al [116]. The catalytic pathway was proved to involve the direct H-transfer to the vinylmercury complex from the aromatic ring. It involved Hg(OTf)2-catalyzed cyclization of aryl 1,1-disubstituted allenes with the formation of a quaternary carbon center followed by the formation of a cationic

Base-free enantioselective S_N2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

• Mili Litvajova,
• Emiliano Sorrentino,
• Brendan Twamley and
• Stephen J. Connon

Beilstein J. Org. Chem. 2021, 17, 2287–2294, doi:10.3762/bjoc.17.146

• ester moieties at C-3 have been shown to participate in enantioselective phase-transfer-catalysed alkylations promoted by ad-hoc designed quaternary ammonium salts derived from quinine bearing hydrogen-bond donating substituents. For the first time in such phase-transfer-catalysed enolate alkylations

• previously been applied to phase-transfer-catalysed SN2 enolate alkylation reactions and represents an effective process for the generation of carbonaceous quaternary stereocentres. The process generates malleable di-ester and mono-ester benzylated oxindole substrates which can easily give access to products

Nomimicins B–D, new tetronate-class polyketides from a marine-derived actinomycete of the genus Actinomadura

• Zhiwei Zhang,
• Tao Zhou,
• Taehui Yang,
• Keisuke Fukaya,
• Enjuro Harunari,
• Shun Saito,
• Katsuhisa Yamada,
• Chiaki Imada,
• Daisuke Urabe and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2021, 17, 2194–2202, doi:10.3762/bjoc.17.141

• , 200.7, and 204.5. In addition, 13C NMR and HSQC analyses revealed the presence of six sp2 carbon atoms (five are proton-bearing), two quaternary sp3 carbon atoms, two oxygen-bearing nonprotonated carbon atoms, six sp3 methine groups (two are oxygenated), six sp3 methylene moieties, and four methyl

• then coupled with the other COSY-defined fragment, C22/C21/C29/C30, by the correlations from H22 to C18 and C23, yielding a cyclohexene ring. This ring was joined together with the dehydrodecalin moiety at the quaternary carbon atom C18 by HMBC correlations from H17 to C18, C19, and C23. As for the

• , 13C NMR, and HSQC spectra revealed the presence of four oxygenated sp2 carbon atoms, three nonprotonated sp2 carbon atoms, six sp2 methine groups, one sp2 methylene unit, one quaternary carbon atom, six sp3 methine groups (two are oxygenated), four sp3 methylene units, and five sp3 methyl groups

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

• unusual di-tert-butylmethyl ester moiety and was limited solely to the alanine derivative [38]. Finally, a Baylis–Hillman-type approach has been employed to realize enantioselective reactions, albeit with a limited scope of substituents at the quaternary carbon [39]. Thus, the development of a general

A study on selective transformation of norbornadiene into fluorinated cyclopentane-fused isoxazolines

• Zsanett Benke,
• Attila M. Remete and
• Loránd Kiss

Beilstein J. Org. Chem. 2021, 17, 2051–2066, doi:10.3762/bjoc.17.132

• the selectivity of olefin bonds during a CM reaction [38][39][40][41][42][43]. Investigations of various types of olefins in CM, such as substituted and functionalized styrenes, unsaturated tertiary alcohols, olefins with quaternary carbon centers, acrylates, allyl ethers or allyl acetates gave a

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• and produce long and uniform polysaccharides. Solvent systems like DMAc/LiCl or quaternary ammonium electrolytes are able to dissolve cellulose and could overcome the precipitation issues during synthesis [55][56]; however, these systems are not always compatible with reaction conditions [57]. The

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• stereogenic centers. Review A plethora of highly effective small‐molecule organocatalysts have enriched the field of organic synthesis [27], including chiral proline derivatives, N‐heterocyclic carbenes, chiral thioureas and Brønsted acids as well as phase‐transfer catalysts (PTC), such as the quaternary

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

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

• . disclosed the quaternary ammonium N-F reagent, N-fluoroquinuclidinium fluoride (6-1) [43]. They subsequently followed with more detailed results in 1988 [44]. Quinuclidine was fluorinated by neat fluorine in trichlorofluoromethane at −72 °C, affording the product 6-1 in 86% yield (Scheme 15). Fluorination

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• established as an excellent strategy for the construction of elaborate molecules. In particular, the hydroalkylation of olefins represents a straightforward strategy for the synthesis of new C(sp3)–C(sp3) bonds, with concomitant formation of challenging quaternary carbon centers. In the last 20 years

• as precursors of nucleophilic radical species in metal hydride hydrogen atom transfer reactions. This unique reactivity, combined with the wide availability of olefins as starting materials and the success reported in the construction of all-carbon C(sp3) quaternary centers, makes hydroalkylation

• reactions an ideal platform for the synthesis of molecules with increased molecular complexity. Keywords: hydroalkylation; hydrogen atom transfer; quaternary carbon center; radical addition; unactivated olefins; Introduction Natural product structures remain some of the main sources of inspiration for the

Chemical synthesis of C6-tetrazole ᴅ-mannose building blocks and access to a bioisostere of mannuronic acid 1-phosphate

• Eleni Dimitriou and
• Gavin J. Miller

Beilstein J. Org. Chem. 2021, 17, 1527–1532, doi:10.3762/bjoc.17.110

• of modified hyaluronic acid fragments [16]. 13C NMR of 5 confirmed the presence of a new quaternary carbon (tetrazole Cq, δC = 155.8 ppm) alongside disappearance of the C6-nitrile (δC = 117.0 ppm). Furthermore, 1H NMR analysis indicated the common H5 doublet was further downfield (δH = 5.64 ppm

Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati,
• Andhika B. Mahardhika,
• Lukas L. Wendt and
• Christa E. Müller

Beilstein J. Org. Chem. 2021, 17, 1464–1475, doi:10.3762/bjoc.17.102

• unsymmetrical 3,3'-diindolylmethanes (DIMs) with a quaternary carbon center has been developed via iodine-catalyzed coupling of trifluoromethyl(indolyl)phenylmethanols with indoles. In contrast to previously reported methods, the new procedure is characterized by chemoselectivity, mild conditions, high yields

• ]. However, synthetic methods for efficient synthesis of unsymmetrical 3,3'-DIMs with a quaternary carbon center, including trifluoromethyl-substituted 3,3'-DIMs, are still rare. Sasaki et al. reported the reaction of trifluoromethyl(indolyl)phenylmethanols with indoles in the presence of trifluoroacetic

• substrate scope and functional group tolerance is highly desirable. As part of our continuous efforts to prepare biologically active DIM derivatives [38], we herein report an innovative approach to synthesize unsymmetrical 3,3'-diindolylmethanes (DIMs) with a fluoromethyl-containing quaternary carbon center

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

• due to two methylenes at δC 38.8 (C-8) and 39.2 (C-9); three methines at δC 46.4 (C-11), 58.4 (C-6), and 77.6 (C-7) as well as two quaternary carbons at δC 45.6 (C-8) and 82.8 (C-10). Correlating 1D data with 2D NMR experiments (1H,1H COSY, 1H,13C HMBC, 1H,1H ROESY, see Figure 2) led to an underlying

• -14, and a methine (C-10, δC 39.3) instead of a hydroxylated quaternary carbon. The presence of the methine C-11 was confirmed by measuring 1D/2D NMR spectra of 3 in chloroform-d (see Table S1 in Supporting Information File 1). The corresponding proton H-11 (δH 3.38) forms again a spin system with H-5