Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• start with the formation of an imine intermediate between the aldehyde function of 33 and the amine 2, followed by a nucleophilic attack by the diketone and a final intramolecular cyclization, the Han group proposes a different pathway, with an initial deprotonation of ketoacid 34 (R2 = Me, Ar, R3 = OH

• of the reactive aryne 80 which is first trapped with the nucleophilic isocyanide to form 81 and then with the electrophilic CO2 (78), to furnish an intermediate benzoic acid derivative 82. Intramolecular cyclization would produce the corresponding isobenzofurane 83, which alternatively, could also be

• involving a sequential enamine formation-Michael addition to produce intermediate 139, followed by intramolecular cyclization to 141 and aromatization through species 142 and 143 (Scheme 40). The cyclization step takes place in a regioselective manner, leading to five-membered heterocycle 141 rather than to

SO₂F₂-mediated transformation of 2'-hydroxyacetophenones to benzo-oxetes

• Revathi Lekkala,
• Ravindar Lekkala,
• Balakrishna Moku,
• K. P. Rakesh and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 976–980, doi:10.3762/bjoc.15.95

• C, which finally undergoes an intramolecular cyclization furnishing the corresponding benzo-oxete 2. The second mechanism starts with the elimination of the proton from the acetyl group next to the carbonyl moiety of the 2'-hydroxyacetophenone 1 in the presence of the base to afford enol

• intermediate I. The latter then reacts with SO2F2 to give intermediate II and fluoride anion. The subsequent deprotonation of intermediate B by the base generates phenol anion III, which finally undergoes an intramolecular cyclization to give the corresponding benzo-oxete 2. Conclusion We have developed a new

Synthesis of 2H-furo[2,3-c]pyrazole ring systems through silver(I) ion-mediated ring-closure reaction

• Vaida Milišiūnaitė,
• Rūta Paulavičiūtė,
• Eglė Arbačiauskienė,
• Vytas Martynaitis,
• Wolfgang Holzer and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2019, 15, 679–684, doi:10.3762/bjoc.15.62

• alkynylation/cyclization reaction between 2-iodophenol and (triethoxysilyl)alkynes [20]. In recent years silver and gold salts have found application as versatile and mild catalysts to access the benzo[b]furan ring system through intramolecular cyclization of 2-alkynylphenol substrates [21], including

• synthetic methods has been developed for the construction of carbon–heteroatom bonds using these types of catalysts. For example, the gold(I) catalyst [(Ph3PAu)3O]BF4 was applied in the regioselective intramolecular cyclization of alkynols to construct bicyclic ethers [37], while the silver(I) catalyst

• AgOTf efficiently catalyzed the intramolecular cyclization of phenoxyethynyl diols into 2,3-unsaturated lactones [38]. In our case, the addition of 10 mol % chloro(triphenylphosphine)gold(I) improved the yield of product 4a to 69% (Table 1, entry 4). However the best results were obtained when AgOTf was

Annulation of 1H-pyrrole-2,3-diones by thioacetamide: an approach to 5-azaisatins

• Aleksandr I. Kobelev,
• Ekaterina E. Stepanova,
• Maksim V. Dmitriev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2019, 15, 364–370, doi:10.3762/bjoc.15.32

• to substitute the S atom and form adduct A. Adduct A underwent a decomposition by releasing a molecule of compound 2 [18]. The formed compound B underwent intramolecular cyclization followed by hydrolysis of the imide group with subsequent decarboxylation and formation of the intermediate C that was

Reusable and highly enantioselective water-soluble Ru(II)-Amm-Pheox catalyst for intramolecular cyclopropanation of diazo compounds

• Hamada S. A. Mandour,
• Yoko Nakagawa,
• Masaya Tone,
• Hayato Inoue,
• Nansalmaa Otog,
• Ikuhide Fujisawa,
• Soda Chanthamath and
• Seiji Iwasa

Beilstein J. Org. Chem. 2019, 15, 357–363, doi:10.3762/bjoc.15.31

• 5 h (Table 2, entry 1). On the other hand, hydroxymethyl Ru(II)-Pheox (cat. 3), which is completely soluble in water, catalyzed the cyclization of 1f affording chiral cyclopropylamide 2f in 97% yield with a high enantioselectivity of 96% in 5 h (Table 2, entry 5) [49]. Next, the intramolecular

• cyclization of trans-allylic diazo Weinreb amide 1f catalyzed by Ru(II)-Amm-Pheox (cat. 2) was examined in various solvents, as shown in Table S1 (Supporting Information File 1). Notably, the catalytic reaction proceeded in a variety of solvents, including aromatic, aliphatic, polar, non-polar, and

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• of MCPs 1 formed the more stable benzyl radical intermediate 5 [45][46], which underwent a ring-opening to generate the alkyl radical 6 [47]. Finally, the desired product 3 was generated through intramolecular cyclization of radical intermediate 6 with an aryl ring and oxidation deprotonation by

• synthesis of 1-naphthaldehydes 25 under mild conditions via a radical-mediated ring-opening and intramolecular cyclization of MCPs 23 with organic selenium reagents 24 (Scheme 8) [59]. In this reaction, the MCPs with electron-withdrawing groups gave lower yields than that with electron-donating groups

• , phenylselenyl radical 26 was produced in the presence of free radical initiator (NH4)2S2O8 [60][61]. Next, the intermediate 26 was added to the C–C double bond of MCPs 23, and then went through a series of ring-opening, intramolecular cyclization, oxidation and dehydrogenation to generate 3

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• . However, when the reaction mixture was warmed to 0 °C before quenching, an intramolecular cyclization occurred under basic conditions to give the oxazolidine (4S,5R)-25 as an almost (>20:1) pure diastereoisomer. The hydroxy group which acted as a nucleophile preferred to attack the re-face of the double

• compound underwent another intramolecular cyclization in the 5-exo mode to form the oxazolidinone 118. To complete the synthesis of (2S,3S,4S)-4 the secondary hydroxy group was protected as a pivalate, the hydroxymethyl fragment was oxidized after hydrolysis of the silyl ether and finally all protecting

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

• single crystal X-ray diffraction study (Figure 2). The sequential domino reaction presumably starts with the Knoevenagel condensation of o-hydroxybenzaldehyde and N-(cyanomethyl)pyridinium salt forming styryl derivative A, which undergoes intramolecular cyclization to give 2-iminochromene salt 3

Synthesis of indole–cycloalkyl[b]pyridine hybrids via a four-component six-step tandem process

• Muthumani Muthu,
• Rakkappan Vishnu Priya,
• Abdulrahman I. Almansour,
• Raju Suresh Kumar and
• Raju Ranjith Kumar

Beilstein J. Org. Chem. 2018, 14, 2907–2915, doi:10.3762/bjoc.14.269

• exclusively, which is evident from the fact that the decahydrocyclododeca[b]pyridin-2-amine 13 anticipated through the intramolecular cyclization of the amino group and the CN in intermediate 10 was not formed in the reaction (Scheme 2). This one-pot four-component strategy was then employed to synthesize

• –cycloalkyl[b]pyridine-3-carbonitrile hybrid heterocycles have been achieved through a facile one-pot four-component strategy. This reaction occurred through a six-step tandem Hantzsch-like process involving Knoevenagel–Michael–nucleophilic addition–intramolecular cyclization–elimination–oxidative

• formation of (E)-3-(4-chlorophenyl)-2-(1H-indole-3-carbonyl)acrylonitrile (8). Simultaneously, the reaction of cyclododecanone (5a) with ammonium acetate affords the enamine 9. The Michael addition of 8 and the enamine 9 yields the intermediate 10. Then the amino group of 10 undergoes intramolecular

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

• , entry 2) shows that the intramolecular cyclization to the ortho-carbon of phenyl ring occurs, most probably, through cation C (Scheme 2). And this reaction has a high activation barrier, analogously to the similar cyclization of phosphonoallenes to the corresponding phosphonoheterocycles [30]. We

• , the atomic coefficient of contribution in the LUMO for sulfur is much higher than for C5. Thus, the electrophilic reactivity of sulfur may be explained by both charge and orbital control. Also, ortho-carbons in the phenyl group bear a negative charge −0.17 to −0.16 e; this means that intramolecular

• cyclization on these atoms is possible. To conclude the study on electronic characteristics of 1,2-oxathiolylium ions A, B by means of NMR and DFT calculations, one should expect that these species may react in several pathways. First, they may undergo nucleophilic attack on sulfur or on carbon C5, due to a

Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles

• Takashi Go,
• Akane Morimatsu,
• Hiroaki Wasada,
• Genzoh Tanabe,
• Osamu Muraoka,
• Yoshiharu Sawada and
• Mitsuhiro Yoshimatsu

Beilstein J. Org. Chem. 2018, 14, 2722–2729, doi:10.3762/bjoc.14.250

• afforded trans-azepines 11d and 12d via intramolecular cyclization. The same procedure applied to the bulky N-(3-methylbut-2-enyl) derivatives 4e and 6e yielded the corresponding diols 9e and 10e. Whether the Pummerer reactions yielded cyclised products or not was strongly affected by the substituent

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

• ], 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

Quinolines from the cyclocondensation of isatoic anhydride with ethyl acetoacetate: preparation of ethyl 4-hydroxy-2-methylquinoline-3-carboxylate and derivatives

• Nicholas G. Jentsch,
• Jared D. Hume,
• Emily B. Crull,
• Samer M. Beauti,
• Amy H. Pham,
• Julie A. Pigza,
• Jacques J. Kessl and
• Matthew G. Donahue

Beilstein J. Org. Chem. 2018, 14, 2529–2536, doi:10.3762/bjoc.14.229

• synthesis method through the one-pot acylation of ethyl acetoacetate with isatoic anhydrides followed by dehydrative intramolecular cyclization to access the desired quinoline scaffold 10 [18]. We replaced sodium hydride as the base required to generate the enolate of ethyl acetoacetate with sodium

Nucleoside macrocycles formed by intramolecular click reaction: efficient cyclization of pyrimidine nucleosides decorated with 5'-azido residues and 5-octadiynyl side chains

• Jiang Liu,
• Peter Leonard,
• Sebastian L. Müller,
• Constantin Daniliuc and
• Frank Seela

Beilstein J. Org. Chem. 2018, 14, 2404–2410, doi:10.3762/bjoc.14.217

• intramolecular cyclization to a macrocycle was not observed. Next, the 5’-azido compound 2 was employed in the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) "click" reaction [38][39] to build up macrocycle 3. In this regard, two reaction pathways have to be considered: (i) an intramolecular “click

• ) sulfate and ascorbic acid. TLC monitoring showed that the cyclization failed. Then, tris(benzyltriazoylmethyl)amine (TBTA) [40][41][42] was added as catalyst and macrocycle 4 was formed in 71% yield, which is extremely high for an intramolecular cyclization. The dimeric product 3 and the cyclic dimer 5

• derivative 4 the dU macrocycle 8 could be isolated in 46% yield even in the absence of TBTA. However, the yield of cyclization was significantly improved when TBTA was added (69%). This demonstrates the influence of the nucleobase on the intramolecular cyclization reaction. All compounds were characterized

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

• Michael R. Imrich,
• Jochen Kraft,
• Cäcilia Maichle-Mössmer and
• Thomas Ziegler

Beilstein J. Org. Chem. 2018, 14, 2082–2089, doi:10.3762/bjoc.14.182

• –Plattner rule [41][42]. Intramolecular cyclization of intermediates 12 and 13 creates the oxazolines 10 and 11. With this model at hand the β:α ratios of entries 1 to 5 in Table 1 can be explained. For R1 = Bn the equilibrium between 9a and 9b is positioned far in favor to 9a. Nucleophilic attack of the

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• was used as a stoichiometric oxidant [45]. In contrast to the intramolecular cyclization, the intermolecular reaction is much more attractive. Li and co-workers reported a syn-diacetoxylation of alkenes, using iodoarenes as catalyst which was oxidized to hypervalent iodine(III) by hydrogen peroxide in

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• 22. The phenolic intermediate 22 is further oxidized with another molecule of PIDA (15) to form intermediate 23, which yielded the final product 19 on intramolecular cyclization [70]. Furthermore, Kita and his research group [71] reported an iodine(III)-mediated cyclization of arylalkynes 24 to

• the substrate. A further treatment with PIDA (15) forms the spirocyclic products through intramolecular cyclization. 2.2. Using hypervalent iodine reagents as catalyst The hypervalent iodine-catalyzed synthesis of spirocylic compounds can be achieved either by using catalytic amounts of a hypervalent

• 2014, Xu and Abdellaoui [93] reported a nucleophilic intramolecular cyclization of phenylacetamides 65 to spirocyclic lactams 66 via iodine(III)-mediated spirocarbocyclizations. In literature, there are limited methods available for the synthesis of spiro-β-lactam-3-carbonitrile which is widely used as

Synthesis of pyrimido[1,6-a]quinoxalines via intermolecular trapping of thermally generated acyl(quinoxalin-2-yl)ketenes by Schiff bases

• Svetlana O. Kasatkina,
• Ekaterina E. Stepanova,
• Maksim V. Dmitriev,
• Ivan G. Mokrushin and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2018, 14, 1734–1742, doi:10.3762/bjoc.14.147

• side-reactions. We found that the intermolecular trapping worked perfectly in case of N5-substituted PQTs 1a–f and did not work at all with N5-unsubstituted PQT 1g and 1h. The failure to obtain products 3o and 3p from PQTs 1g and 1h can be explained by the occurrence of intramolecular cyclization in

• (quinoxalin-2-yl)ketenes. Side-reactions concurring with intermolecular trapping of ketene generated from PQT 1a by benzalaniline (2a). Formation of furoquinoxalines 6a,b via intramolecular cyclization in ketenes generated from PQTs 1g,h. Thermal characteristics of decarbonylation of PQTs 1a–h. Intermolecular

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• ]. Treatment of the thiol-ene 113 with the radical initiator 2,2-dimethoxy-2-phenylacetophenone (DPAP) and the photosensitizer 4-methoxyacetophenone (MAP) in DMF ensued to the formation of the thiyl radical 114 that underwent intramolecular cyclization to provide a mixture of biologically important thiosugars

• -hydroxy sulfide 134 that subsequently underwent intramolecular cyclization into thiazepine 135. Further manipulations led to the formation of diltiazem (12) as its hydrochloride salt. The second route (route B), which is similar to the first, entailed biocatalytic resolution of the enantiomers using a

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• and 2-iodomesitylene (2a). Intramolecular cyclization leads to the iminofuranylium intermediate B which affords the cationic isoindolin-1-one structure C via subsequent intramolecular aza-Michael type rearrangement. This intermediate reacts in the final step with the electron-rich 2-iodomesitylene (2a

Methyl isocyanide as a convertible functional group for the synthesis of spirocyclic oxindole γ-lactams via post-Ugi-4CR/transamidation/cyclization in a one-pot, three-step sequence

• Amarendar Reddy Maddirala and
• Peter R. Andreana

Beilstein J. Org. Chem. 2018, 14, 875–883, doi:10.3762/bjoc.14.74

• gaseous byproduct. Furthermore, compound 6 is proposed to undergo an intramolecular cyclization, under basic conditions, yielding target compounds 7 (Scheme 2). Results and Discussion Our initial synthetic attempts began with the Ugi-4CR involving stoichiometrically equal amounts of 2-(Boc-amino

• intramolecular cyclization proceeded smoothly using K2CO3/MeCN reflux conditions and products 7b–k were obtained in good to excellent yields (Scheme 4). Although the results shown only reflect the use of K2CO3/MeCN reflux conditions, similar, if not exact reaction outcomes were observed when conditions from

• ) and methyl isocyanide (4) in a one-pot reaction process to generate compound 6b from 5b. In all cases, the Michael acceptor [52] (intermediate II) was generated in situ from 6b, under basic conditions (Table 1, entry 1, K2CO3/MeCN/reflux), followed by the intramolecular cyclization proceeding through

Anodic oxidation of bisamides from diaminoalkanes by constant current electrolysis

• Tatiana Golub and
• James Y. Becker

Beilstein J. Org. Chem. 2018, 14, 861–868, doi:10.3762/bjoc.14.72

• suggested that the analysis will be done immediately after terminating the electrolysis. Characterization of products See Supporting Information File 1 for spectral data and copies of 1H and 13C NMR spectra. Anodic oxidation of amides. Anodic oxidation of an amide in the presence of alkene. Intramolecular

• cyclization via anodic oxidation of an eneamide. Anodic bond cleavages in amides of type Ph2CHCONHAr. Type of products obtained (n = 0, 1, 2). Synthesized cyclic N-acyl and N-sulfonyl piperidines for electrolysis. Type of bisamides (derived from diamines) studied (n = 2, 3, 4). Type of products obtained from

Preparation of trinucleotide phosphoramidites as synthons for the synthesis of gene libraries

• Ruth Suchsland,
• Bettina Appel and
• Sabine Müller

Beilstein J. Org. Chem. 2018, 14, 397–406, doi:10.3762/bjoc.14.28

• aqueous dioxane and subsequent spontaneous intramolecular cyclization leading to cleavage of the ester bond and release of the free 3'-OH group [29] (Figure 4A). Also with 3'-O-TBDMS-protected monomers as mentioned above, a full set of trimers representing codons of all 20 amino acids was synthesized

The selective electrochemical fluorination of S-alkyl benzothioate and its derivatives

• Shunsuke Kuribayashi,
• Tomoyuki Kurioka,
• Shinsuke Inagi,
• Ho-Jung Lu,
• Biing-Jiun Uang and
• Toshio Fuchigami

Beilstein J. Org. Chem. 2018, 14, 389–396, doi:10.3762/bjoc.14.27

• cleavage nor benzene ring fluorination took place at all. Finally, the anodic fluorination of benzothioates having a γ and δ-carboxyl group, 1m and 1n, was examined. The anodic oxidation of 1m and 1n proceeded; however, α-fluorination did not occur. In both cases, an anodic intramolecular cyclization took

• of an α-cationic intermediate, the intramolecular cyclization seems to take place faster than combination with a fluoride ion as shown in Scheme 6. In support of this, we have reported a fluoride ion-promoted anodic cyclization of α-(phenylthio)-N-phenyl- and α-(phenylthio)-N-benzylacetamides [28] as

• -(ω-carboxy)alkyl benzothioates afforded intramolecular cyclization products like lactones instead of the corresponding α-fluorinated products. Experimental General information 1H, 13C and 19F NMR spectra were recorded on a JEOL JNM EX-270 (1H: 270 MHz, 13C: 67.8 MHz, 19F: 254.05 MHz) spectrometer in

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

• Jun Ki Kim,
• Hwan Jung Lim,
• Kyung Chae Jeong and
• Seong Jun Park

Beilstein J. Org. Chem. 2018, 14, 243–252, doi:10.3762/bjoc.14.16

• facile preparation of thienyl heterocycles 8. The mechanism for this reaction is based on the formation of a sulfur ylide-like intermediate. It was clearly suggested by (i) the intramolecular cyclization of ketene N,S-acetals 7 to the corresponding thiophenes 8, (ii) 1H NMR studies of Meldrum’s acid

• tetrasubstituted thiophenes via the intramolecular cyclization of S-alkylated heterocyclic–aryl dithioesters [56]. However, these approaches are limited by the multistep synthesis (Figure 2A) [54][55] and the complicated dithioester preparation (Figure 2B) [56]. In general, tetrasubstituted thiophenes have

• yielding [57][62]. Thus, a new mild synthetic route for the synthesis of 5-(pyridyl)thiophenes is required. We therefore investigated the synthesis of thienylpyridines using a metal-free approach. Results and Discussion At first, our efforts focused on the intramolecular cyclization reactions with mild