Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

• ), where the eight-membered ring was accessed through a SmI2-mediated cyclization cascade reaction of a dialdehyde [69]. In this approach, an original way was proposed to form in a single step the tricyclic core of pleuromutilin (1) with a stereocontrol at the four contiguous stereocenters [69][70]. The

• dialdehyde was obtained from trans-dihydrocarvone (141) and treated early in the sequence (step 13/34) by SmI2. The authors assumed that the cascade reaction was initiated with the left-hand aldehyde ketyl formation 146 which further attacked the alkene and oriented the anti-5-exo-trig-cyclization toward (Z

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• dependence [95]. On the other hand, simple benzyl cations can undergo more controlled (3 + 2) annulations, as is illustrated by the long-known Friedel–Crafts-type acid-catalyzed cascade reaction of styrene leading to the cyclic styrene dimer 86 (Scheme 13c) [96][97]. This (3 + 2) cycloaddition reactivity of

Practical synthesis of isocoumarins via Rh(III)-catalyzed C–H activation/annulation cascade

• Qian-Ci Gao,
• Yi-Fei Li,
• Jun Xuan and
• Xiao-Qiang Hu

Beilstein J. Org. Chem. 2023, 19, 100–106, doi:10.3762/bjoc.19.10

• to couple iodonium ylides with enaminones in a Rh(III)-catalyzed C–H activation/annulation cascade reaction for the rapid construction of isocoumarins (Scheme 1c). Results and Discussion Our initial experiment was performed with enaminone 1a and iodonium ylide 1b in the presence of [Cp*RhCl2]2 (5 mol

• obtained by using [{Ru(p-cymene)Cl2}]2 as a catalyst (Table 1, entry 10). With the optimal conditions in hand, we then investigated the scope of this Rh-catalyzed C–H activation/annulation cascade reaction. As shown in Scheme 2, a range of functionalized enaminones were compatible with this Rh-catalytic

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• a semipinacol rearrangement leading to 95, followed by subsequent cyclization to natural products guignardone A (96) and C (97). This process involved 1,2-allyl migration and C–O bond formation through a semipinacol rearrangement and a cyclodehydration cascade reaction (Scheme 8). Following the same

Navigating and expanding the roadmap of natural product genome mining tools

• Friederike Biermann,
• Sebastian L. Wenski and
• Eric J. N. Helfrich

Beilstein J. Org. Chem. 2022, 18, 1656–1671, doi:10.3762/bjoc.18.178

• , terpene cyclases generate the oftentimes multicyclic, hydrocarbon scaffold via a carbocation-mediated cascade reaction [30]. Terpene cyclases are obligatory components of canonical terpene pathways and are used to identify terpene BGCs (Figure 3B) [30][31]. RiPPs, on the other hand, lack genes that are

Synthesis of (−)-halichonic acid and (−)-halichonic acid B

• Keith P. Reber and
• Emma L. Niner

Beilstein J. Org. Chem. 2022, 18, 1629–1635, doi:10.3762/bjoc.18.174

• acids. Keywords: alkaloid; amino acid; aza-Prins reaction; cascade reaction; natural product; Introduction Marine sponges produce a large number of structurally diverse natural products, including many that exhibit biological activity [1][2][3]. In 2019, Tsukamoto and co-workers isolated the

Synthetic study toward the diterpenoid aberrarone

• Liang Shi,
• Zhiyu Gao,
• Yiqing Li,
• Yuanhao Dai,
• Yu Liu,
• Lili Shi and
• Hong-Dong Hao

Beilstein J. Org. Chem. 2022, 18, 1625–1628, doi:10.3762/bjoc.18.173

• were reported [30][31] and more recently, Carreira and co-workers reported [32] the first total synthesis of aberrarone through an impressive cascade reaction including a gold-catalyzed Nazarov cyclization, a cyclopropanation followed by intramolecular aldol reaction to forge the A, B and D rings

One-pot double annulations to confer diastereoselective spirooxindolepyrrolothiazoles

• Juan Lu,
• Bin Yao,
• Desheng Zhan,
• Zhuo Sun,
• Yun Ji and
• Xiaofeng Zhang

Beilstein J. Org. Chem. 2022, 18, 1607–1616, doi:10.3762/bjoc.18.171

• equiv) with 86% of isolated yield and 1.1:1.0 of 1a/4a through decarboxylative [3 + 2] cycloaddition (Table 1, entry 6), which afforded compound 5a with 73% isolated yield at 90 °C for 9 h. Notably, we conferred cascade reaction process to synthesize compound 5a with 70% isolated yield as one-step four

Oxa-Michael-initiated cascade reactions of levoglucosenone

• Julian Klepp,
• Thomas Bousfield,
• Hugh Cummins,
• Sarah V. A.-M. Legendre,
• Jason E. Camp and
• Ben W. Greatrex

Beilstein J. Org. Chem. 2022, 18, 1457–1462, doi:10.3762/bjoc.18.151

• bridged α,β-unsaturated ketones; however, these reactions do not involve initiation by an oxa-Michael addition [23][24]. The reaction between 1 and aromatic ketones under basic conditions is analogous to the well-known aldol/Michael cascade reaction observed between aldehydes and enolates giving di- and

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

• Estelle Silm,
• Ivar Järving and
• Tõnis Kanger

Beilstein J. Org. Chem. 2022, 18, 167–173, doi:10.3762/bjoc.18.18

• molecular complexity. There are many examples of the organocatalytic synthesis of fused cycles starting from the cyclohexane-1,3-dione. For example, Rueping et al. demonstrated that the cyclohexane-1,3-dione undergoes a cascade reaction with α,β-unsaturated aldehydes [4] and they later employed the method

Chemical and chemoenzymatic routes to bridged homoarabinofuranosylpyrimidines: Bicyclic AZT analogues

• Sandeep Kumar,
• Jyotirmoy Maity,
• Banty Kumar,
• Sumit Kumar and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2022, 18, 95–101, doi:10.3762/bjoc.18.10

• pyridine to afford dimesylated nucleosides 16a,b in 93 and 94% yields, respectively. The reaction of nucleosides 16a,b with NaOH in dioxane/water (1:1) underwent a cascade reaction pathway to form 9a,b in 82 and 84% yields, respectively (Scheme 4). The overall yields for the synthesis of nucleosides 9a,b

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

• the yields, whereas the electronic properties of the substituents on the indole ring did. In 2019, Lin and co-workers reported the asymmetric three-component cascade reaction of 2,3-diketo esters 28, aromatic amines 29, and 1,3-cyclohexanediones 30 to prepare axially chiral arylindoles 31 in a highly

• catalyst developed by our group is critical for increasing the enantioselectivity in this cascade reaction [38]. This catalyst can facilitate the aldol reaction to generate a stereocenter (I-7), which can then be converted to axial chirality (I-8 to I-10) and finally aromatized to give 31 (Scheme 11) [60

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

• al. reported cinchona-based primary amine catalyzed cascade aza-Michael-aldol reaction of α,β-unsaturated ketones 6 with 2-(1H-pyrrol-2-yl)-2-oxoacetates 5 where triphenylacetic acid was used as an additive. This cascade reaction afforded highly functionalized chiral pyrrolizines 8 in good yields (70

• tertiary amine-thiourea catalyst (cat. 82). This cascade reaction afforded aza-Michael adducts in 77–92% yields with high ee (up to 90%) (Table 19) [55]. Du et al. developed an enantioselective catalytic tandem aminolysis/aza-Michael addition for the asymmetric total synthesis of two natural Apocynaceae

• . accomplished an asymmetric organocatalytic quadruple cascade reaction of various α-ketoamides 111 with aromatic α,β-unsaturated aldehydes 112 to obtain tetraaryl-substituted 2-azabicyclo[3.3.0]octadienones 114 in good yields (34–71%) with excellent diastereo- and enantioselectivities (84–97%). The reaction

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

• Yi Liu,
• Puying Luo,
• Yang Fu,
• Tianxin Hao,
• Xuan Liu,
• Qiuping Ding and
• Yiyuan Peng

Beilstein J. Org. Chem. 2021, 17, 2462–2476, doi:10.3762/bjoc.17.163

• trifluoromethylated coumarins [59], we recently developed a Rh-catalyzed approach to trifluoromethyl-substituted pyrroles using the Togni reagent II as trifluoromethyl source. It involves a three-component cascade reaction of 1,3-enynes, anilines, and Togni reagent II to afford fully substituted pyrrole derivatives

Targeting active site residues and structural anchoring positions in terpene synthases

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2021, 17, 2441–2449, doi:10.3762/bjoc.17.161

• (GFPP, C25) for sesterterpene biosynthesis. Type I terpene synthases (TPSs) activate these acyclic molecules by the abstraction of diphosphate to produce a reactive allyl cation that can initiate a cascade reaction through typical carbocation chemistry, including cyclisation reactions by intramolecular

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

• hydroquinolinone, chromene, piperidine, peptide, lipid, and glycoside moieties (Scheme 2). Bojanowski and co-workers developed a methodology to synthetize 3,4-dihydrocoumarins 10 through a decarboxylative and dearomatizative cascade reaction [33]. This reaction was carried out using coumarin-3-carboxylic acids 8

• cascade reaction. Total synthesis of (+)-smyrindiol (17). Michael addition of 4-hydroxycoumarin (1) to enones 2 through a bifunctional modified binaphthyl organocatalyst 18. Michael addition of ketones 20 to 3-aroylcoumarins 19 using a cinchona alkaloid-derived primary amine catalyst 22. Enantioselective

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• investigated by means of DFT calculations using the reaction between enaminone 6a and phenyl azide. TS1 and TS2 have been proposed as two transition states, which then converted to IN1 and IN2 as two possible isomers. The stable final products were achieved via a cascade reaction including the elimination of

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

• stereogenic centers were constructed by this cascade reaction. As exemplified above (Scheme 23), the hypothesized enolate intermediate produced in the radical conjugate addition promoted by a MHAT process could be engaged in sequential reactions, offering a range of possibilities for the design of new

• additions [92]. Using MBH acetates 63 as substrates, olefin hydroallylation products 64 were obtained via E1cB elimination of the acetate leaving group driven by the enolate intermediate (Scheme 25B). Six-membered lactones (Scheme 25A, 65a–c) were obtained in a cascade reaction when alkenyl alcohols were

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

• derivatives. Keywords: 4-aryltetralin-2-ol; 5-aryl-benzo[7]annulen-7-ol; cascade reaction; Prins/Friedel–Crafts; Introduction 2,4-Disubstituted tetralins (Figure 1, 1), especially 2-functionalized tetralins are privileged building blocks for medicinal chemistry applications which are known to exhibit a wide

• structure is shown in Figure 3 [27]. Conclusion In summary, a Prins cyclization and Friedel–Crafts cascade reaction strategy for the synthesis of 4-aryl-tetralin-2-ols and 5-aryl-tetrahydro-5H-benzo[7]annulen-7-ols has been established. The sequence involved the Prins cyclization of 2-(2-vinylphenyl

• of 2-(2-vinylphenyl)acetaldehyde (13a). Modified synthesis of 2-(2-vinylphenyl)acetaldehydes 13a–g and 1-vinyl-2-naphthaldehyde (13h). Lewis acid-catalyzed Prins/Friedel–Crafts reaction of 13a with veratrole. Use of different nucleophiles for the cascade reaction with 13a. Reaction conditions: a

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• cancer cells. Keywords: γ-carboline; cascade reaction; cell uptake; cytotoxicity; fluorescence; Introduction Carbolines are privileged aza-heterocycles found in the core of several natural and synthetic compounds and are known for their biological applications. Among the four different isomers, 9H

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

• by introducing a nucleophile into the enol ether, which traps the reactive oxocarbenium ion intermediate 60, leading to the formation of THP [39]. The first example of an MAP cascade reaction was reported by Rychnovsky and co-workers using allylsilane 62 as an internal nucleophile, as shown in Scheme

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• prepared the (−)-adaline (1) and the non-natural isomer (−)-euphococcinine (2) through a four-step intramolecular Mannich cyclization cascade reaction [57]. In this methodology, the alkaloids were prepared by treating the convenient N-sulfinylamino ketone ketal precursor on heating with NH4OAc:HOAc. Oxo

• %, respectively. The conversion of precursors N-sulfinylamino ketone ketals directly to the desired homotropanes represents a four-step intramolecular Mannich cyclization cascade reaction, being the most efficient method to date for the (−)-adaline (1) and (−)-euphococcinine (2) syntheses. Specific rotation was

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• radical precursors in this system, allowing for both alkyl [44] and acyl [45] RCA reactions. In the case of acyl DHPs, they propose that direct excitation of the DHP leads to radical generation rather than the iminium intermediate (Scheme 9c). The same system was used for the radical cascade reaction

• separately developed a Minisci-type reaction using phthalimide esters 123; however, their system did not extend past isoquinoline substrates 124 (Scheme 17b) [62]. Zheng and Studer expanded the scope of this type of reactivity to a three-component cascade reaction with alkyl bromides 125 and enamides 126

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts

• Soundararajan Karthikeyan,
• Radha Krishnan Shobana,
• Kamarajapurathu Raju Subimol,
• J. Helen Ratna Monica and
• Ayyanoth Karthik Krishna Kumar

Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130

• : phosphonium salt-catalysed triazolation of MBH adducts. Scope of the one-pot cascade reaction of the unprotected Morita–Baylis–Hillman adducts 3a–q. Comparative analysis of the sequential one-pot reaction. Optimization of the triazolation of the MBH adduct 1a. Optimization of the reaction conditions for 3

Palladium-catalyzed regio- and stereoselective synthesis of aryl and 3-indolyl-substituted 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones

• Valeria Nori,
• Antonio Arcadi,
• Armando Carlone,
• Fabio Marinelli and
• Marco Chiarini

Beilstein J. Org. Chem. 2020, 16, 1084–1091, doi:10.3762/bjoc.16.95

• pleased to report here that this cascade reaction takes place efficiently, resulting in the regio- and stereoselective formation of the poly-substituted isoquinolinones 4 in good to high yield. Applications of this reaction can be relevant for improvements of structure diversity and fine tuning of the