Allostreptopyrroles A–E, β-alkylpyrrole derivatives from an actinomycete Allostreptomyces sp. RD068384

• Marwa Elsbaey,
• Naoya Oku,
• Mohamed S. A. Abdel-Mottaleb and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2024, 20, 1981–1987, doi:10.3762/bjoc.20.174

• ; HRESITOFMS (m/z): [M – H]– calcd for C15H22NO4, 280.1554; found, 280.1550. Allostreptopyrrole B (2): greenish yellow amorphous solid; +15 (c 0.10, MeOH); UV (MeOH) λmax, nm (log ε): 235 (3.87), 273 sh (3.49); IR (ATR) νmax: 3263, 2964, 2925, 2854, 1658, 1556, 1417 cm−1; 1H and 13C NMR data, see Table 2

• ; HRESITOFMS (m/z): [M – H]– calcd for C15H22NO4, 280.1554; found, 280.1554. Allostreptopyrrole C (3): greenish yellow amorphous solid; −6.1 (c 0.10, MeOH); UV (MeOH) λmax, nm (log ε): 235 (3.82), 276 sh (3.46); IR (ATR) νmax: 3265, 2925, 2856, 1657, 1555, 1417 cm−1; 1H and 13C NMR data, see Table 2

• , 332.1832; found, 332.1838. Methylation of 1 Allostreptopyrrole A (1, 2.0 mg, 0.007 mmol) and K2CO3 (4.4 mg, 0.032 mmol) were stirred in dry DMF (0.5 mL) at 50 °C for 10 min. Methyl iodide (19 μL, 0.32 mmol) was added and the mixture was stirred at this temperature for 12 h [29]. Reaction completion was

Development of a flow photochemical process for a π-Lewis acidic metal-catalyzed cyclization/radical addition sequence: in situ-generated 2-benzopyrylium as photoredox catalyst and reactive intermediate

• Masahiro Terada,
• Zen Iwasaki,
• Ryohei Yazaki,
• Shigenobu Umemiya and
• Jun Kikuchi

Beilstein J. Org. Chem. 2024, 20, 1973–1980, doi:10.3762/bjoc.20.173

• , initiating further radical reactions through the formation of radical cations B. Nucleophilic arylmethyl radicals C, which are generated from radical cations B by desilylation, undergo an addition reaction with 2-benzopyrylium intermediates A, giving rise to the corresponding radical cation. Catalytic cycle

• 2a, and 0.5 mmol (5 equiv) of TFA under light irradiation (blue LED: λmax = 448 nm) at 50 °C for 1 h in 1 mL (total volume) of 1,2-DCE] [55] with a flow rate of 3 mL/h (light irradiation time: 20 min in the flow reaction, 1 h in the batch reaction). As shown in Table 1, product 3a was obtained in

• moderate yield (entry 1: 42%, cf. batch reaction: 76%). Lowering the reaction temperature to 25 °C reduced the yield (Table 1, entry 2: 35%), but decreasing the amount of the phosphine ligand from 20 mol % to 5 mol % markedly improved the yield (Table 1, entry 3: 53%). Even when the flow rate was increased

Radical reactivity of antiaromatic Ni(II) norcorroles with azo radical initiators

• Siham Asyiqin Shafie,
• Ryo Nozawa,
• Hideaki Takano and
• Hiroshi Shinokubo

Beilstein J. Org. Chem. 2024, 20, 1967–1972, doi:10.3762/bjoc.20.172

• the electrophile [16][17][18]. In addition, C–C double bonds of the norcorrole skeleton outside the π-delocalization pathway exhibit a reactivity similar to an alkene to afford hydrogenated norcorroles by hydrogenation [19] or reduction with hydrazine [20] and [3 + 2]-cycloadducts with 1,3-dipoles [21

• core. For the byproducts, 3a would be generated through the quenching of radical I with a hydrogen atom source. Bisdipyrrin 4a could be formed through the ring-opening reaction of I by the homolytic cleavage of the C(sp2)–C(sp2) bond to radical II, the addition of the isobutyronitrile radical, and

1,2-Difluoroethylene (HFO-1132): synthesis and chemistry

• Liubov V. Sokolenko,
• Taras M. Sokolenko and
• Yurii L. Yagupolskii

Beilstein J. Org. Chem. 2024, 20, 1955–1966, doi:10.3762/bjoc.20.171

• magnesium [50][51] to form the desired 1,2-difluoroethylene as a mixture of E- and Z-isomers, which were separated by fractional distillation (boiling point: −53.1 °C for (E)-HFO-1132 and −26.0 °C for (Z)-HFO-1132 [47]). In patent literature, a variety of synthetic routes to HFO-1132 starting from other

• cis-isomer decreases, i.e., the cis-isomer of 1,2-difluoroethylene is thermodynamically favored [47]. Deuteration The stereospecific reaction of (E/Z)-1,2-difluoroethylene with a 1–2 M solution of NaOD in D2O (90–120 °C, 2 d) led to the formation of CDF=CDF with high isotopic purity (Scheme 8) [76][77

• ]. Additionally, when the reaction was performed using DMSO-d6 (or CD3CN) and CH3ONa, H/D exchange occurred already at ambient temperature (25 °C, 20 h) [78]. The formation of CDF=CDF was confirmed by NMR spectroscopy, namely by the change of signal multiplicity in the 19F NMR spectra of E- and Z-isomers of 1,2

Regioselective alkylation of a versatile indazole: Electrophile scope and mechanistic insights from density functional theory calculations

• Pengcheng Lu,
• Luis Juarez,
• Paul A. Wiget,
• Weihe Zhang,
• Krishnan Raman and
• Pravin L. Kotian

Beilstein J. Org. Chem. 2024, 20, 1940–1954, doi:10.3762/bjoc.20.170

• similar to 6. They observed high N1-selectivity using NaH in THF with pentyl bromide and electron-deficient indazoles, postulating a coordination of the indazole N2-atom and an electron-rich oxygen atom in a C-3 substituent with the Na+ cation from NaH. Under anhydrous conditions the yields ranged from 44

• % at room temperature to 89% when warmed to 50 °C. No information was provided to justify any N2-selectivity or the lack thereof. Should an N2–Cs+–O ion pair exist, this could reasonably account for all the reported results presented herein (vide infra). Additionally, using Cs2CO3 in dioxane provided

• S1 in Supporting Information File 1. Stoichiometric manipulation of 12 to 6 in DMF at 90 °C provided the N1-substituted product P1 in 52–60% yields. The yields of P1 formation were largely unaffected in DMF with temperatures ranging from room temperature to 110 °C. Varying the equivalents of Cs2CO3

A new platform for the synthesis of diketopyrrolopyrrole derivatives via nucleophilic aromatic substitution reactions

• Vitor A. S. Almodovar and
• Augusto C. Tomé

Beilstein J. Org. Chem. 2024, 20, 1933–1939, doi:10.3762/bjoc.20.169

• Vitor A. S. Almodovar Augusto C. Tome LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal 10.3762/bjoc.20.169 Abstract Diketopyrrolopyrroles (DPPs) are a versatile group of dyes and pigments with valuable optoelectronic properties. In this work we report the

• , 120 °C, 2 h) resulted in very low yields (6–16%) for the formation of N,N’-bis(pentafluorobenzyl)-DPP derivatives [36]. Changing the base to NaH and performing the reaction at a lower temperature, enabled to obtain DPP 2 in a reasonable yield (61%) and allowed us to use it as a starting material for

• chromatography (TLC) was carried out on precoated sheets with silica gel (Merck 60, 0.2 mm thick). Preparative TLC was carried out on 20 cm × 20 cm glass plates precoated with a layer of silica gel 60 (0.5 mm thick) and activated in an oven at 100 °C for 12 h. Melting points were determined with a Büchi B-540

Negishi-coupling-enabled synthesis of α-heteroaryl-α-amino acid building blocks for DNA-encoded chemical library applications

• Matteo Gasparetto,
• Balázs Fődi and
• Gellért Sipos

Beilstein J. Org. Chem. 2024, 20, 1922–1932, doi:10.3762/bjoc.20.168

• access to compounds featuring C(sp2)–C(sp3) bonds. However, the general view is that this transformation is less reliable than its orthogonal counterpart, the Suzuki reaction. Recent years have seen significant developments in Negishi reaction methodologies [34][35][36][37][38][39]. In particular

Solvent-dependent chemoselective synthesis of different isoquinolinones mediated by the hypervalent iodine(III) reagent PISA

• Ze-Nan Hu,
• Yan-Hui Wang,
• Jia-Bing Wu,
• Ze Chen,
• Dou Hong and
• Chi Zhang

Beilstein J. Org. Chem. 2024, 20, 1914–1921, doi:10.3762/bjoc.20.167

• isoquinolinone derivatives. The method provides highly chemoselective access to 3- or 4-substituted isoquinolinone derivatives by reacting o-alkenylbenzamide derivatives with PISA in either acetonitrile or wet hexafluoro-2-isopropanol. Keywords: annulation; C–H amination; hypervalent iodine reagent; iodine(III

• zwitterionic water-soluble hypervalent iodine reagent (phenyliodonio)sulfamate (PISA). In water, PISA is strongly acidic, and the pH value can reach 2.05 in a saturated aqueous solution. With PISA, various indoles have been synthesized via C–H amination of 2-alkenylanilines involving an aryl migration

• , isopropyl, cyclopropyl, phenyl, or hydrogen, respectively, the intramolecular amination smoothly gave the corresponding 4-substituted isoquinolinone products 2b,c,d–f in 51–94% yield. Notably, when 1c was used as the substrate, the cycloisomerization product 2c' was observed in 31% yield besides 2c in 51

Novel oxidative routes to N-arylpyridoindazolium salts

• Oleg A. Levitskiy,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2024, 20, 1906–1913, doi:10.3762/bjoc.20.166

• amount (5%) of the N,N’-diaryldihydrophenazine radical cation that is the byproduct corresponding to the intermolecular oxidative C–N coupling of the diarylamine A1 was detected in the reaction mixture. This emphasizes that the both processes are of the same nature and proceed through the same

• intermediate (i.e., the diarylamines’ radical cation) and indicates the dominance of the intramolecular cyclization over the intermolecular C–N coupling process. Oxidation of diarylamines in the presence of an excess of trifluoroacetic acid gave no targeted pyridoindazolium salts, whereas the amount of

• previous mechanistic study [20][21] which revealed that the intermolecular C–N and C–C couplings are disfavored in case of the diarylamines with two electron-deficient phenyl rings. To our surprise, the procedure did not work in the case of amine A3: only traces of pyridoindazolium salt S3 were detected in

Access to 2-oxoazetidine-3-carboxylic acid derivatives via thermal microwave-assisted Wolff rearrangement of 3-diazotetramic acids in the presence of nucleophiles

• Ivan Lyutin,
• Vasilisa Krivovicheva,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 1894–1899, doi:10.3762/bjoc.20.164

• cyclization [15][16]. Additionally, the manganese(III)-promoted cyclization of N-alkenyl malonamides [17][18] and the Cu(I)-catalyzed reaction of propiolic acid derivatives with nitrones (Kinugasa reaction) [19][20][21] should also be mentioned, as well as intramolecular C–H insertion using

• tested in a previous study [3]. The reaction requires rather severe heating under microwave irradiation (200 °C, chlorobenzene, sealed vial), ensuring complete conversion of the diazo compound in a rather short time. Initial experiments using p-anisidine as a nucleophile showed that the target β-lactam

• derivative 3a could be obtained in high yield (83%) after simple chromatographic separation of the reaction mixture (Scheme 2). When the synthesis was carried out using conventional heating in 1,2-dichlorobenzene (200 °C, 1 h), product 3a was obtained in slightly lower yield (75%), so further experiments

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• synthesis (DOS) where a single methodology should generate diverse scaffolds. This comprehensive review focuses on all these aspects, and has been divided into five chapters, describing, respectively: a) efforts to develop new and milder reaction conditions; b) the use of new building blocks; c) the

• on different substrates, the conditions were similar: 20 mol % of the catalyst, ethanol as solvent at 80 °C in the first case, 30 mol % of catalyst, ethylene glycol at 90 °C in the second case; however, a striking difference appears when the reaction was carried out in the absence of silver catalyst

• , reported that, by using hexafluoroisopropanol (HFIP) as the solvent, GBB adducts derived from glycal aldehydes could be isolated without additional catalysts in a few hours at 25–50 °C [10]. In this case, however, the role of the solvent as a Brønsted acid cannot be ruled out (this article will be

A facile three-component route to powerful 5-aryldeazaalloxazine photocatalysts

• Ivana Weisheitelová,
• Radek Cibulka,
• Marek Sikorski and
• Tetiana Pavlovska

Beilstein J. Org. Chem. 2024, 20, 1831–1838, doi:10.3762/bjoc.20.161

• bearing electron-donating or halogen groups. This practical method is characterised by atom economy and offers a direct route to the introduction of an aryl moiety into the C(5)-position of deazaalloxazines, thereby generating novel catalysts for photoredox catalysis without the need for subsequent

• (All) and also 5-deazaflavins (dFl) and 5-deazaalloxazines (dAll), where the N(5) atom of the isoalloxazine/alloxazine core is replaced by a C–H moiety (Figure 1A). In particular, 5-deazaflavins have generated considerable interest from scientists to study flavin-catalysed reactions in enzymatic and

• -deazaflavins [11][12][13]. Recently, it has been discovered that both 5-deazaflavins 1 and 5-deazaalloxazines 2, which have an aryl substituent in position C(5), form stable radicals that act as powerful reductive photocatalysts with a reducing power comparable to that of lithium [E*(1/1•) = −3.3 V vs SCE

Hetero-polycyclic aromatic systems: A data-driven investigation of structure–property relationships

• Sabyasachi Chakraborty,
• Eduardo Mayo Yanes and
• Renana Gershoni-Poranne

Beilstein J. Org. Chem. 2024, 20, 1817–1830, doi:10.3762/bjoc.20.160

• structural resolution: a) global properties, b) atomic composition, and c) building block composition. At each of these levels, we analyzed the data according to various structural features, to elucidate the underlying structure–property relationships and delineate clear principles that can aid in rational

• separated and colored by the longest L for: A) all 9-ring molecules; B) all 9-ring molecules that do not have an antiaromatic moiety in the longest linear stretch; C) all 9-ring molecules that do not contain any antiaromatic moiety. The KDEs are normalized such that the area under each curve is 1

• . Distributions of molecular properties for 4n and (4n + 2) π-electron count systems, divided by the number of rings for: A) HOMO and LUMO energies and B) Gaps. Stacked histograms showing the prevalence of the different heteroatoms across different areas of the property space, for A) HOMO, B) LUMO, C) Gap, D) AIP

Discovery of antimicrobial peptides clostrisin and cellulosin from Clostridium: insights into their structures, co-localized biosynthetic gene clusters, and antibiotic activity

• Moisés Alejandro Alejo Hernandez,
• Katia Pamela Villavicencio Sánchez,
• Rosendo Sánchez Morales,
• Karla Georgina Hernández-Magro Gil,
• David Silverio Moreno-Gutiérrez,
• Eddie Guillermo Sanchez-Rueda,
• Yanet Teresa-Cruz,
• Brian Choi,
• Armando Hernández Garcia,
• Alba Romero-Rodríguez,
• Oscar Juárez,
• Siseth Martínez-Caballero,
• Mario Figueroa and
• Corina-Diana Ceapă

Beilstein J. Org. Chem. 2024, 20, 1800–1816, doi:10.3762/bjoc.20.159

• filter as their presence is not needed for biosynthesis, albeit it is for resistance. As a result, the C. cellulovorans 743 clusters were chosen because they were thought to be complete, novel, and most interesting, primarily due to the presence of two different, apparently independent operons, each with

• cluster of C. cellulovorans 743, clostrisin and cellulosin were compared with known lanthipeptides, generating a similarity network made using the percent identity between the precursor peptides from all experimentally characterized lanthipeptides to date (Figure 3A). We found it noteworthy to examine the

• function–structure relationships and how they impact biological activity. Since we have not found evidence of horizontal transfer of the cloA1 and cloA2 gene clusters, it is an interesting speculation that they could constitute the origin of this family and that, by duplicating one of these clusters, C

Chiral bifunctional sulfide-catalyzed enantioselective bromolactonizations of α- and β-substituted 5-hexenoic acids

• Sao Sumida,
• Ken Okuno,
• Taiki Mori,
• Yasuaki Furuya and
• Seiji Shirakawa

Beilstein J. Org. Chem. 2024, 20, 1794–1799, doi:10.3762/bjoc.20.158

• catalysts in the asymmetric bromolactonization of 5-hexenoic acid derivatives without additional substituents on the carbon–carbon double bond (Scheme 2). The catalytic asymmetric bromolactonization of model substrate 2a with N-bromophthalimide (NBP) was conducted at −78 °C for 24 hours using chiral

Oxidative fluorination with Selectfluor: A convenient procedure for preparing hypervalent iodine(V) fluorides

• Samuel M. G. Dearman,
• Xiang Li,
• Yang Li,
• Kuldip Singh and
• Alison M. Stuart

Beilstein J. Org. Chem. 2024, 20, 1785–1793, doi:10.3762/bjoc.20.157

• -molecule drugs contain at least one fluorine atom [2]. Hypervalent iodine(III) fluorides, such as difluoroiodotoluene 1 and fluoroiodane 2, have been key to the development of numerous, new synthetic procedures for C–F bond formation over the last decade. Since difluoroiodotoluene 1 has low chemical

• iodine(I) precursor 8 (Table 1). Reacting 8 with 4 equivalents of trichloroisocyanuric acid (TCCA) and 6 equivalents of potassium fluoride in dry acetonitrile at 40 °C for 48 hours formed difluoroiodane 6 in a 90% spectroscopic yield (Table 1, entry 1). An iodosyl decomposition product 9 was also formed

• fluorinating reagent (Table 1, entry 5). When 8 was reacted with 4 equivalents of freeze-dried Selectfluor in dry acetonitrile at 40 °C for 48 hours, difluoroiodane 6 was formed in 85% spectroscopic yield. However, the iodosyl decomposition product 9 was also produced in 15% spectroscopic yield, despite

Ugi bisamides based on pyrrolyl-β-chlorovinylaldehyde and their unusual transformations

• Alexander V. Tsygankov,
• Vladyslav O. Vereshchak,
• Tetiana O. Savluk,
• Serhiy M. Desenko,
• Valeriia V. Ananieva,
• Oleksandr V. Buravov,
• Yana I. Sakhno,
• Svitlana V. Shishkina and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2024, 20, 1773–1784, doi:10.3762/bjoc.20.156

• , azomethines based on aromatic amines and substituted pyrrolecarbaldehyde [40] or pyrrolyl-β-chlorovinylaldehyde [39], contain several frequently encountered motifs in drugs and drug candidates – a pyrrole heterocycle and an azomethine C=N fragment (Figure 1) – and exhibit some biological activity. Thus, Ugi

• -component Ugi reaction (Ugi-3CR) with preliminary synthesis of azomethines 9a–c (Table 1). In this case, the Ugi bisamides 5, 6, 8 were formed, however, it was found that the application of the Ugi-3CR approach had no significant effect on the yields of the target products. Considering the additional

• experience of the authors [27][32], we tried to apply the described hydrolysis conditions (5 equiv HCl in MeOH) to our products (compounds 5). As a model reaction, we heated a mixture of Ugi bisamide 5d and an aqueous solution of HCl in methanol (glycerol bath, 80 °C) in a hermetically sealed vial with

Synthesis and characterization of 1,2,3,4-naphthalene and anthracene diimides

• Adam D. Bass,
• Daniela Castellanos,
• Xavier A. Calicdan and
• Dennis D. Cao

Beilstein J. Org. Chem. 2024, 20, 1767–1772, doi:10.3762/bjoc.20.155

• steric demands of the N-phenyl groups, there are also C–H···π interactions between phenyl groups of adjacent π stacks, with the closest Ph centroid to H distance being 2.613 Å (Figure 2a). Additionally, the middle carbonyl oxygens are in short contact (2.376 Å) with the 7- and 8-H atoms of the

• from the title compounds. Despite this different packing mode within the stack, the interstack interactions exhibited by 8-Ph are similar to those found in 7-Ph. Although there are still observable C–H···π interactions and C=O···H–C interactions between stacks, they appear to be weaker, as evidenced by

• the longer interaction distances and interceding incorporation of CH2Cl2 (Figure 2b). Furthermore, in 8-Ph the interstack C=O···H–C interaction is skewed such as to involve only one C=O, compared to the symmetric dual-contact that is seen for 7-Ph. Optical and electronic characterization The

Harnessing unprotected deactivated amines and arylglyoxals in the Ugi reaction for the synthesis of fused complex nitrogen heterocycles

• Javier Gómez-Ayuso,
• Pablo Pertejo,
• Tomás Hermosilla,
• Israel Carreira-Barral,
• Roberto Quesada and
• María García-Valverde

Beilstein J. Org. Chem. 2024, 20, 1758–1766, doi:10.3762/bjoc.20.154

• more complex systems, we explored post-condensation reactions on the 2-nitrobenzylamine and 3-bromopropylamine derivatives. Thus, we carried out the reduction of the nitro group on derivatives 5b and 5h employing tin(II) chloride and chlorhydric acid in boiling n-butanol (120 °C), conditions previously

• [29], through post-condensation reactions. Following the methodology previously described in our group [30], the reduction of the nitro group on indole and pyrrole derivatives 9f,g,l–o (Scheme 9, Table 5) employing tin(II) chloride under acidic conditions in boiling n-butanol (120 °C) afforded the

• characterisation. Funding Funding from MCIN/AEI/10.13039/501100011033 [grant PID2020-117610RB-I00] is gratefully acknowledged. J. G.-A. and I. C.-B. thank Consejería de Educación de la Junta de Castilla y León, European Social Fund (ESF) and ERDF for their predoctoral (J. G.-A.) and post-doctoral (I. C.-B

Synthesis of polycyclic aromatic quinones by continuous flow electrochemical oxidation: anodic methoxylation of polycyclic aromatic phenols (PAPs)

• Hiwot M. Tiruye,
• Solon Economopoulos and
• Kåre B. Jørgensen

Beilstein J. Org. Chem. 2024, 20, 1746–1757, doi:10.3762/bjoc.20.153

• after removal of solvents from the reaction mixture. Thus, Et4NOTs can easily be recycled and reused for a greener reaction. Voltammetric studies To investigate their redox behaviour, PAPs 1a,b (Figure 1A), 3a–c (Figure 1C), and 6a–c (Figure 1E) were scanned between +2.2 V and −1.5 V. All compounds

• cations B and C which have only one Clar sextet with two alternative positions. Conclusion The electrochemical oxidation of polycyclic aromatic phenols to quinones represents a green alternative to chemical oxidants. Hydrogen gas evolution can be handled by recycling of the reaction mixture through the

• electrochemical flow cell to achieve high yields. Better yields are obtained with C/Pt electrode pair and methanol in the absence of water during the oxidation. The position of the hydroxy group controls the position of the quinone acetal to form a single product. p-Quinones are formed when the para-position to

Syntheses and medicinal chemistry of spiro heterocyclic steroids

• Laura L. Romero-Hernández,
• Ana Isabel Ahuja-Casarín,
• Penélope Merino-Montiel,
• Sara Montiel-Smith,
• José Luis Vega-Báez and
• Jesús Sandoval-Ramírez

Beilstein J. Org. Chem. 2024, 20, 1713–1745, doi:10.3762/bjoc.20.152

• mesylate 1, whose basic treatment promoted the substitution of the mesylate group at C-21 by the 17α-hydroxy group and the oxetane ring formation in a 16% yield (Scheme 1) [10]. Winkler et al. developed the synthesis of alkylated derivatives of 17-spirooxetanosteroids from non-alkylated frameworks (Scheme

• . The oxetane compound 6 was further derivatized to incorporate a pyrrolidine moiety in presence of ammonia. Upon debenzylation at C-3, the target compound 7 was obtained in an 18% overall yield from 3. The pyrrolidino-oxetane derivative exhibited potent inhibition of Hedgehog signaling, comparable to

• -Methylene spirolactones at C-3 11a and 11b derived from dihydrocholesterol and stanolone were also obtained in 41% and 52% yields, respectively (dr > 20:1) (Scheme 3). More recently, a functionalized spiro-β-lactone was obtained via a metal-free procedure involving photoinduced carbene C–H insertion in a

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

• Ryo Tanifuji and
• Hiroki Oguri

Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151

• prenyltransferase (PT) domain located at the C-terminus of BscA (Scheme 2A). Subsequently, the terpene cyclase (TC) domain at the N-terminal of BscA generates fusicocca-2,10(14)-diene (6), which bears the common 5/8/5 fused tricyclic scaffold common to this natural products family. Sequential oxidative conversions

• skeletal rearrangement, providing the distinct skeleton of 11 via carbocation C. This rearrangement involves the preferential migration of an alkenyl group in C to the carbocation, followed by deprotonation at C18 to form an exo-olefin. β-face-selective hydroxylation at C12 in 11 by the P450 enzyme BscG

• the chemical conversion. Site- and diastereocontrolled hydrogenation of the resulting exomethylene in 27 yielded brassicicene C (28). Further diastereoselective reduction of the C13 ketone completed the total synthesis of brassicicene H (29). By integrating the convergent and scalable chemical

A fiber-optic spectroscopic setup for isomerization quantum yield determination

• Anouk Volker,
• Jorn D. Steen and
• Stefano Crespi

Beilstein J. Org. Chem. 2024, 20, 1684–1692, doi:10.3762/bjoc.20.150

• conclusion holds for any photoswitch where only one isomer can be isolated successfully. During the measurement and at the PSS, the relative concentrations of the two isomers are unknown. The total absorbance (Absobs) at a given total concentration (c) of the sample is a linear combination of the absorbance

• of each isomer, as illustrated by Equation 1. The value for c at the PSS can be found using other spectroscopic methods, such as NMR spectroscopy [17] or the TEM (for Thulstrup, Eggers, and Michl) method [34][35]. With a known value for c, the spectrum of the second component can be found by a simple

• constant for the thermal back isomerization is 7.2∙10−7 s−1 at 20 °C [24]. This value is generally disregarded for routine experiments where the isomerization happens in the minute timescale, however we explicitly included it in our quantum yield determination for better accuracy. Using the Beer–Lambert

Oxidation of benzylic alcohols to carbonyls using N-heterocyclic stabilized λ³-iodanes

• Thomas J. Kuczmera,
• Pim Puylaert and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2024, 20, 1677–1683, doi:10.3762/bjoc.20.149

• tetrazine salt 1c. Based on these results, the reaction conditions were further optimized using NHI 1a with the benzyl alcohols 3a (electron-rich) and 3b (electron-poor) as the model substrates. First, the reaction temperature was increased, finding 60 °C to be the optimal value in EtOAc (Table 1, entry 1

• -activated iodane of this type, a mixture of NHI 1a and HCl in EtOAc was stirred for 1 h at 60 °C and an ESI(−) mass spectrum was recorded afterward, showing an ion I-OMe with m/z 337.0 [1a – OH + MeO + Cl]− (Scheme 1c). It is known that methanol, which is used as a solvent in the mass spectrometer, can be

• equiv) and method A: aqueous HCl (37%, 500 µmol, 41.6 µL, 1.00 equiv) in EtOAc (2.5 mL) or method B: TBACl (500 µmol, 137 mg, 1.00 equiv) in MeCN (2.5 mL), respectively, were stirred at 60 °C for 2.5 h, quenched with Me2S (2.00 equiv) and the reaction mixture was purified via flash column chromatography

Ring opening of photogenerated azetidinols as a strategy for the synthesis of aminodioxolanes

• Henning Maag,
• Daniel J. Lemcke and
• Johannes M. Wahl

Beilstein J. Org. Chem. 2024, 20, 1671–1676, doi:10.3762/bjoc.20.148

•  1), we successfully conducted the desired sequence by raising the temperature to 100 °C to initiate ring opening, and employing a mild transesterification method for diol release [43][44][45]. Thus, we were able to isolate 3-amino-1,2-diol 21 in 49% yield. Conclusion Within this work, we