Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• reactions (anthracene (33) and maleic anhydride (34) to the cycloaddition adduct 35 and chromene carbaldehyde 36 and enol ether 37 to the diastereomeric pyrano-chromenes 38), Alder-En reactions (oxomalonate diethyl ester (39) and β-pinene (40) to give the α-pinene derivative 41), and the thermal

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

• methodology for aerobic C–H activation; ii) PEG as green and recyclable reaction medium; and iii) a reusable palladium catalyst complex [65]. Fully functionalized 1,2,3-triazolo-fused chromenes 162, 164, and 166 were regioselectively prepared in moderate yield. The isoindoline-fused triazoles 164 were

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• -hydroxyaryl)enones underwent cyclization to ketals (chromanols) after the addition of boronic acid. The prepared chromanols afforded the chromenes through elimination upon treatment with p-TsOH. A series of different β-(2-hydroxyaryl)enones and boronic acids was tested and provided the substituted chromenes

• ][65][66][67]. Flowchart for the selection of the proper catalytic system. First example of asymmetric addition of organoboron reagents to cyclic enones [32][33]. Addition of arylboronic acids to enones accelerated by silver salts [34][35]. Synthesis of chromenes by the 1,4-addition of boronic acids to

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

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• beyond 3000 years have been achieved [14]. Unlike most of the widely applied photochromes (spiropyrans, spirooxazines, chromenes, dithienylethenes, etc.), both forms of hemi-indigo absorb in the visible light region. Therefore, photochemical switching does not require the use of the UV light, which is of

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

• Olga A. Storozhenko,
• Alexey A. Festa,
• Delphine R. Bella Ndoutoume,
• Alexander V. Aksenov,
• Alexey V. Varlamov and
• Leonid G. Voskressensky

Beilstein J. Org. Chem. 2018, 14, 3078–3087, doi:10.3762/bjoc.14.287

• annulation patterns. Biologically relevant imidazo[1,2-a]pyridines and chromenes. General view of the molecule 7b in the crystal state (CCDC 1849215). Anisotropic displacement parameters are drawn at 50% probability. Domino formation of imidazopyridines and current work. Scope of the reaction between N

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• recently shown [8]. These allenes give rise to pyrrolidines [9], pyrroles [10], chromenes [11], benzoazepinones [12], macrolides [13], and some other carbo- and heterocycles [14][15][16]. It should be specially emphasized that many compounds containing SO2 groups are drugs, such as, dapson [17], oxicams

Assembly of fully substituted triazolochromenes via a novel multicomponent reaction or mechanochemical synthesis

• Robby Vroemans,
• Yenthel Verhaegen,
• My Tran Thi Dieu and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2689–2697, doi:10.3762/bjoc.14.246

• intermediate 3-nitro-2H-chromenes with organic azides in a one-pot two-step sequence. The triazolochromenes were formed with complete regioselectivity and new biologically relevant structures were synthesized via extension of the developed procedure and via postfunctionalization. The mechanochemical synthesis

• -triazole; Introduction Chromenes are important structural motifs and are omnipresent in nature and drugs for medicinal applications [1][2][3][4]. Vitamin E [5][6][7][8], arahypin-5 [9][10], THC and other cannabinoids [11][12][13][14] are only a few examples of biologically relevant chromenes. Hence, the

• ], via intramolecular cyclization of a diazomethane group and a nitrile [23], or via our recently reported NH-triazole synthesis starting from 6-methoxyflavanone [24]. Furthermore, 1,4,5-trisubstituted 1,2,3-triazole annulated chromenes have been reported via an intramolecular arylation reaction of 1,2,3

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• dimers formed in a Diels–Alder dimerization process by heating the corresponding Mannich bases under reflux in dichloromethane for 2 hours. In the synthesis of 3,4-dihydro-2-aryl-2H-benzo[f]chromenes and 2-aryl-6,7-dimethylchromans starting from substituted styrenes and 1-dimethylaminomethyl-2-naphthol

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• structures that can be further transformed into interesting potential biologically active heterocyclic derivatives such as terpenoid pyranes, lactones, (hydro)chromenes or pyridines, among others [23][24][25][26]. Depending on the connection of the two isoprene units, four different kinds of dimers can be

A practical way to synthesize chiral fluoro-containing polyhydro-2H-chromenes from monoterpenoids

• Oksana S. Mikhalchenko,
• Dina V. Korchagina,
• Konstantin P. Volcho and
• Nariman F. Salakhutdinov

Beilstein J. Org. Chem. 2016, 12, 648–653, doi:10.3762/bjoc.12.64

• , 630090 Novosibirsk, Russian Federation 10.3762/bjoc.12.64 Abstract Conditions enabling the single-step preparative synthesis of chiral 4-fluoropolyhydro-2H-chromenes in good yields through a reaction between monoterpenoid alcohols with para-menthane skeleton and aldehydes were developed for the first

• time. The BF3·Et2O/H2O system is used both as a catalyst and as a fluorine source. The reaction can involve aliphatic aldehydes as well as aromatic aldehydes containing various acceptor and donor substituents. 4-Hydroxyhexahydro-2H-chromenes were demonstrated to be capable of converting to 4

• -fluorohexahydro-2H-chromenes under the developed conditions, the reaction occurs with inversion of configuration. Keywords: chirality; fluorine; halo-Prins reaction; isopulegol; monoterpene; Introduction Recently, we have found that a reaction between para-mentha-6,8-dien-2,3-diol (1) and aromatic aldehydes in

Copper-mediated arylation with arylboronic acids: Facile and modular synthesis of triarylmethanes

• H. Surya Prakash Rao and
• A. Veera Bhadra Rao

Beilstein J. Org. Chem. 2016, 12, 496–504, doi:10.3762/bjoc.12.49

• . Recently, we reported a copper-catalyzed C–C bond formation by substitution of the labile C(4)SMe group in 4H-chromenes or C(3)–OH in isoindolinones with aryl/alkenyl groups by employing the corresponding boronic acids [51][52]. Continuing these efforts, we designed a copper-catalyzed synthesis of a

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• malonates 65 to 3-nitro-2H-chromenes 66, which provided the substituted chromanes 67 in moderate to excellent yields and good enantioselectivities (Scheme 23) [33]. Catalyst (S,S)-68 is postulated to catalyze the reaction in a bifunctional manner: the tertiary amine deprotonates the malonate and the

• two anomers. In 2012, Xie and his group envisioned the use of α,α-dicyano olefins 90, as a vinylogous Michael donor in an asymmetric Michael addition to substituted 3-nitro-2H-chromenes 91 catalyzed by bifunctional thiourea catalyst 92 (Scheme 31) [50]. When R2 is an alkyl group the reaction resulted

• tested and the desired products were isolated in good to excellent yields (up to 98%), diastereoselectivities (up to 99:1) and enantioselectivities (up to 98%). In 2010, Xie and co-workers reported the kinetic resolution of racemic 3-nitro-2H-chromenes 130 catalyzed by Takemoto’s organocatalyst 77

Facile synthesis of 4H-chromene derivatives via base-mediated annulation of ortho-hydroxychalcones and 2-bromoallyl sulfones

• Srinivas Thadkapally,
• Athira C. Kunjachan and
• Rajeev S. Menon

Beilstein J. Org. Chem. 2016, 12, 16–21, doi:10.3762/bjoc.12.3

• furnished 3-arylsulfonyl-4H-chromene derivatives in 58–67% yield (18 examples). 2-Bromoallyl sulfones functioned as synthetic surrogates for allenyl sulfones in the reaction. Keywords: allenes; chromenes; cyclocondenzation; sulfones; vinylic substitution; Findings Benzo[b]dihydropyran, commonly known as

• cell death [4]. The natural chromene rhodomyrtone (Figure 1) is known to exhibit potent antibacterial activity [5]. As a consequence, a number of methods have been developed for the synthesis of substituted 4H-chromenes [6]. This includes, inter alia, transition metal-mediated cyclizations [7

• -sulfonyl-4H-chromenes from o-hydroxychalcones and 2-bromoallyl sulfones was developed. The starting materials are easily available and the reaction conditions are mild. 2-Bromoallyl sulfones 2a,b functions as stable surrogates for the sensitive allenyl sulfones in this reaction. Functionalities such as

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

• Danielle L. Paterson and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

• both possess a highly functionalised furo[2,3-b]chromene ring system (Figure 2, highlighted in blue) and differ only with the nature of the ketone side-chain. Furo[2,3-b]chromenes have not been reported in any other natural products to date with the closest related system being the chromeno[2,3-b

• ]chromenes. Compound which contain this motif, such as albanol A and australisine A, display potent bioactive properties including hypotensive, anticancer, antimicrobial and antimalarial activity [10][11][12]. The unique ring system found in the hyperaspidinols combined with the potent biological activities

• -diol 22 in quantitative yield. Finally, stirring of ketal 22 in a 1:1 2 M HCl (aq):THF resulted in removal of the ketal protecting group, giving ketone 8, which under the acidic condition immediately cyclized giving furo[2,3-b]chromenes 7a and 7b in a 1.6:1 ratio, in an overall 84% yield. Separation of

Synthesis of 2-trifluoromethylpyrazolo[5,1-a]isoquinolines via silver triflate-catalyzed or electrophile-mediated one-pot tandem reaction

• Xiaoli Zhou,
• Meiling Liu,
• Puying Luo,
• Yingjun Lai,
• Tangtao Yang and
• Qiuping Ding

Beilstein J. Org. Chem. 2014, 10, 2286–2292, doi:10.3762/bjoc.10.238

• example, 2-perfluoroalkynoates have been widely used in synthesizing fluorinated heterocycles, such as benzodiazepines [22], chromenes [21][25], and 2-oxopyridine-fused 1,3-diazaheterocycles [26]. As part of our ongoing efforts in developing synthetic approaches for the functionalization of isoquinoline

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

• G. Gangadhararao,
• Ramesh Kotikalapudi,
• M. Nagarjuna Reddy and
• K. C. Kumara Swamy

Beilstein J. Org. Chem. 2014, 10, 996–1005, doi:10.3762/bjoc.10.99

• series include phosphonobenzofurans/indenones [21][22], -pyrazoles [23], -chromenes/thiochromenes [24][25], -pyrroles [26], multiply substituted furans [27], indolopyran-1-ones [28], N-hydroxyindolinones [29], and oxindoles [30]. In the reaction shown in Scheme 1a, for the formation of the

Gold(I)-catalyzed hydroarylation reaction of aryl (3-iodoprop-2-yn-1-yl) ethers: synthesis of 3-iodo-2H-chromene derivatives

• Pablo Morán-Poladura,
• Eduardo Rubio and
• José M. González

Beilstein J. Org. Chem. 2013, 9, 2120–2128, doi:10.3762/bjoc.9.249

• preparation of elusive 4-unsubstituted-3-iodo-2H-chromenes has been accomplished as result of a catalytic cyclization. Thus, upon exposition of [(3-iodoprop-2-yn-1-yl)oxy]arenes to IPrAuNTf2 (3 mol %), in 1,4-dioxane at 100 °C, the desired heterocyclic motif is readily assembled. This process nicely tolerates

• inhibitors [23], the metal-catalyzed coupling reaction of nitrogen-containing nucleophiles with 3-halo-substituted chromenes has been recognized as a convenient synthetic tool, which provides smooth access to potentially useful candidates [24]. The required halogen containing building-blocks can be prepared

• -chromenes (see Scheme 1, entries a and b, respectively). However, they fail to produce simple 3-halo-4-unsubstituted derivatives. This synthetic context suggests a timely opportunity for devising new protocols to access the latter class of 3-halo-2H-chromene scaffolds from readily available precursors

Catalytic asymmetric tandem Friedel–Crafts alkylation/Michael addition reaction for the synthesis of highly functionalized chromans

• Jiahuan Peng and
• Da-Ming Du

Beilstein J. Org. Chem. 2013, 9, 1210–1216, doi:10.3762/bjoc.9.137

• stereogenic centers [1][2][3][4][5][6][7][8][9][10][11][12][13]. Newly developed tandem/domino reactions are increasingly applied in the synthesis of natural products and other biologically active compounds [14][15][16]. Dihydrocoumarins, chromans, and chromenes can be found in many natural products and

• [21][22][23][24][25][26][27][28][29][30][31][32]. Chiral indolyl(nitro)chromans have been successfully synthesized in our previous study [33]. Good results were obtained in the diastereo- and enantioselective Friedel–Crafts alkylation of indoles with 3-nitro-2H-chromenes catalyzed by diphenylamine

Reactions of salicylaldehyde and enolates or their equivalents: versatile synthetic routes to chromane derivatives

• Ishmael B. Masesane and
• Zelalem Yibralign Desta

Beilstein J. Org. Chem. 2012, 8, 2166–2175, doi:10.3762/bjoc.8.244

• summarized retrosynthetically in Scheme 1. This review will summarize the reported methods for the syntheses of chromane derivatives from the reaction of salicylaldehyde and enolates or their equivalents. For the purposes of this review, chromane derivatives will include flavans, flavones, chromenes and

• ) and α,β-unsaturated compounds 48–51 in the synthesis of the corresponding chromenes 52–55 (Scheme 19) [39]. These reactions were performed in water as the solvent and the chromenes were isolated in yields of 71–79%. It is instructive to note that the Baylis–Hillman products were not detected or

• isolated in this work. The mechanism of the DABCO-catalyzed reaction of salicylaldehyde and α,β-unsaturated compounds in the synthesis 3-substituted chromenes was proved to proceed through the Baylis–Hillman reaction by Kaye and co-workers [40][41] Their work involved the reaction of salicylaldehyde (5

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• most significant synthetic methods reported on chiral-amine-catalyzed tandem Michael conjugate addition of heteroatom-centered nucleophiles to α,β-unsaturated compounds followed by cyclization reactions for the enantioselective construction of functionalized chiral chromenes, thiochromenes and 1,2

• -dihydroquinolines in optically enriched forms found in a myriad of bioactive natural products and synthetic compounds. Keywords: chromenes; 1,2-dihydroquinolines; enantioselective; Michael addition; organocatalytic; thiochromenes; Introduction Chromenes or benzopyrans and their sulfur and nitrogen analogues are

• six membered mono hetero-atom containing, biologically active heterocycles, such as functionalized chromenes (benzopyranes), thiochromenes (thiobenzopyranes) and 1,2-dihydroquinolines, by means of tandem/domino hetero Michael addition reactions, or modified versions [33][34][35][36][37][38], covering

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• devices. Many different organic photochromic molecules are known in photochemistry, such as azobenzenes, stilbenes, spiropyranes, fulgides, diarylethenes and chromenes among many others (Figure 1) [16]. The photochromic processes that take place when such compounds are illuminated can be divided in three

Synthesis of axially chiral oxazoline–carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe₂

• Feijun Wang,
• Shengke Li,
• Mingliang Qu,
• Mei-Xin Zhao,
• Lian-Jun Liu and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 726–731, doi:10.3762/bjoc.8.81

• diaminocarbene) gold(I) complexes 3 derived from 3,3′-substituted 1,1′-binaphthalenyl-2,2′-diamine, and their application in the dynamic kinetic asymmetric transformation of propargyl esters, giving the corresponding substituted chromenes in up to 99% ee [12]. Our group also developed a new family of axially

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• -carbon atoms of allenylidene-Ru 92 complex were attacked giving rise to the corresponding chromenes and 1-substituted 1H-naphtho[2,1-b]pyrans 93, respectively, in moderate to excellent yields (Scheme 35). Electron-withdrawing as well as electron-donating functional groups were tolerated on the phenol

• ) Propargylation of arenes with stoichiometric amounts of the Ru-allenylidene complex 86. (B) First catalytic propargylation of (hetero)arenes using a cationic Ru-complex. Diruthenium-catalyzed formation of chromenes and 1H-naphtho[2,1-b]pyrans. Rhenium(V)-catalyzed FC propargylations as a first step in the total

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• was investigated by time-resolved absorption spectroscopy in the picosecond time domain. Keywords: benzopyrans; chromenes; naphthopyrans; palladium-mediated coupling reactions; photochromism; Introduction Interest in photoswitchable chromophores for the material and life sciences has increased

• (closed forms), also referred to as chromenes, leads to the formation of interconverting photoisomers of the open merocyanine-type (quinoidal, zwitterionic and hybrid forms and their stereoisomers), depending upon the substitution pattern of the parent pyrans and the conditions employed (Scheme 1

• . The transient was recorded at 470 nm (black) and is shown together with a single-exponential fit (red) yielding a decay time of 12 μs. Photochromism of 2H-chromenes. Synthesis of functionalized pyrans from 2-bromo-3H-naphtho[2,1-b]pyrans and 3-bromo-2H-1-benzopyrans by palladium-mediated