Entry to new spiroheterocycles via tandem Rh(II)-catalyzed O–H insertion/base-promoted cyclization involving diazoarylidene succinimides

• Alexander Yanovich,
• Anastasia Vepreva,
• Ksenia Malkova,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 561–569, doi:10.3762/bjoc.20.48

• %). Under these conditions, the 5-endo-dig cyclization leading to the target spirobutenolide 2a proceeded rather slowly (about 25% conversion per day). However, an attempt to accelerate the reaction by using a stronger base (DBU) resulted in side processes with the formation of unwanted impurities, whereas

Recent developments and trends in the iron- and cobalt-catalyzed Sonogashira reactions

• Surendran Amrutha,
• Sankaran Radhika and
• Gopinathan Anilkumar

Beilstein J. Org. Chem. 2022, 18, 262–285, doi:10.3762/bjoc.18.31

• . This synthetic protocol offers increased functional group tolerance and moderate to good yields of the products by the coupling of various functional group-substituted acetylenes with o-iodophenol. The proposed mechanistic study involves a Sonogashira coupling followed by a 5-endo-dig cyclization

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

• standard conditions. The proposed catalytic cycle included aza-Michael addition of arylamines, Lewis acid copper(II)-catalyzed intramolecular 5-endo-dig cyclization, protonation, and oxidation to provide the final products, tetrasubstituted pyrroles 39. The introduction of a trifluoromethyl group into

• products 52 were obtained efficiently through the cascade reactions of enynals 51, primary amines, aliphatic isocyanides, and trimethylsilyl azide. The following reaction involves Ag-catalyzed intramolecular 5-endo-dig cyclization and base (DMAP)-promoted oxidative isomerization. The presence of DMAP is

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• when using C,N-, N,S- and N,N-dinucleophiles. It is characterized by a selective 5-endo-dig cyclization to the corresponding five-membered rings. The obtained new compounds are of special interest due to the practical utility of the formed fused heterocycles, such as indoles [1], thiazolo[2,3-b][1,3,4

• ]thiadiazole [2], and benzo[4,5]imidazo[2,1-b]thiazole [3], as well as due to the simultaneous presence of a biologically active phosphorus function in the molecules. Recently, we have shown that the reaction of chloroethynylphosphonates with 2-aminopyridines proceeds through a 5-endo-dig cyclization to form

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

• cyclization of readily available 4-alkynyl-3-hydroxy-1H-pyrazoles can be used as an efficient method to access many novel 2,5-disubstituted 2H-furo[2,3-c]pyrazoles. Keywords: 5-endo-dig cyclization; 2H-furo[2,3-c]pyrazole; pyrazole; silver(I) catalyst; Sonogashira coupling; Introduction Heterocyclic ring

• construction of the 2H-furo[2,3-c]pyrazole ring system by a Sonogashira-type alkynylation of 4-iodopyrazol-3-ol and subsequent intramolecular 5-endo-dig cyclization of the obtained hydroxyalkynyl substrate mediated by a Ag(I) catalyst. Results and Discussion The synthetic strategy designed to construct the 2H

•  1, entry 1). The formation through a 5-endo-dig cyclization of some amount of compound 4a was detected by LC–MS measurements only when the reaction mixture contained Cs2CO3 as a base and was heated at 120 °C for 4 days (Table 1, entry 2). Surprisingly, when K2CO3 was used instead of Cs2CO3, the

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

• cyclization product 7a and not the 4-exo-dig-cyclization compound 7a' (Scheme 3). We rationalized, as per Baldwin’s rules, that the 5-endo-dig cyclization of a 1,4-Michael addition was more favorable than the 4-exo-dig-cyclization [50][51]. The structure of compound 7a was definitively confirmed by X-ray

• the exception of AgOTf/DCM (Table 1, entry 6), led to the formation of the desired 5-endo-dig cyclization product 7a and none of the 4-exo-dig cyclization product 7a' was observed. In Table 1, entries 2–5 and 7 show moderate product yields whereas entries 1 and 8 show superior yields of >80%. With the

• spirocyclic 2-oxindoles. Post-Ugi-4CR/transamidation/cyclization sequence. Base-promoted intramolecular 5-endo-dig cyclization. Reaction scope with varying combinations of substrates. Synthesis of 5-chloro-1'-phenylspiro[indoline-3,2'-pyrrolidine]-2,5'-dione (8a). Method applicability for the one-pot

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• %) and the optimal temperature was 60 °C. The aryl moieties on alkynes and glyoxals tolerated the presence of ED and EW groups. The proposed mechanism implied the coupling among reaction partners to give an α-amino-β,γ-ynone intermediate I capable to undergo a 5-endo-dig cyclization by an intramolecular

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• as two carbon cycloaddition partners and IPrAuNTf2 as catalyst [Au2, IPr = bis(2,6-diisopropylphenyl)], is shown in Scheme 4. The reaction is initiated by a 5-endo-dig cyclization of the carbonyl oxygen onto the Au-activated C–C triple bond, giving rise to the oxocarbenium intermediate VIII. The

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• involves mild conditions and short reaction times. 3.3 Amides, sulfamides and ureas as nucleophiles Using AuPPh3Cl/Ag2CO3-catalyzed 5-endo-dig cyclization in water under microwave irradiation, our group developed a fast and green route to prepare indole-1-carboxamides 137 from N'-substituted N-(2

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• . Cyclopropanes 85a are generated in situ by intermolecular cyclopropanation of enyne 84 and a carbene resulting from the rearrangement of propargyl ester 83. When tertiary propargyl esters are used, the 5-endo-dig cyclization generates the carbocation 89. Migration of the pivaloyloxy group affords the allylic

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• substituent at the alkyne terminus. An initial 5-endo-dig cyclization of the lactam nitrogen to the metal-activated alkyne was proposed, followed by the fragmentation of the lactam amide bond and the formation of an acyl cation. The above chemistry was extended to non-aromatic substrates, providing a new

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

• cyclocondensation of alkyne diols to give substituted furans (Scheme 3, Reaction 3) [35]. Our objective, laid out in Scheme 4, was to initiate cycloisomerization with a 5-endo-dig cyclization of the homopropargyl alcohol 6, followed by 5-exo-trig cyclization onto the resulting dihydrofuran, whilst avoiding

• methanol. Path a, which corresponds roughly to our original experimental designs, involves initial gold-catalyzed 5-endo-dig cyclization to dihydrofuran 18. Once the regiochemistry is established, any number of condensation pathways would lead to spiroketal 17. For example, protonation of the enol ether

First synthesis of 2-(benzofuran-2-yl)-6,7-methylene dioxyquinoline-3-carboxylic acid derivatives

• Wentao Gao,
• Jia Liu,
• Yun Jiang and
• Yang Li

Beilstein J. Org. Chem. 2011, 7, 210–217, doi:10.3762/bjoc.7.28

• construction of the benzofuran moiety from intermediate 5. For the construction of 2-substituted benzofurans, the most widely used approach involves the palladium-catalyzed heteroannulation of 2-halophenols with a terminal alkyne via a tandem Sonogashira coupling-5-endo-dig-cyclization, largely based on the