Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• report from the literature [24] a plausible reaction mechanism is shown in Scheme 6. It involves the nucleophilic attack of the aminopyridine 1 to the HPW-activated carbonyl compound 2, followed by iminium ion formation (iii) and [4 + 1] cycloaddition with the isocyanide. A 1,3-hydrogen shift yields the

Tandem Hock and Friedel–Crafts reactions allowing an expedient synthesis of a cyclolignan-type scaffold

• Viktoria A. Ikonnikova,
• Cristina Cheibas,
• Oscar Gayraud,
• Alexandra E. Bosnidou,
• Nicolas Casaretto,
• Gilles Frison and
• Bastien Nay

Beilstein J. Org. Chem. 2024, 20, 162–169, doi:10.3762/bjoc.20.15

• dihydronaphthalene 4. One-pot conversion of substrate 1 into 1-aryltetraline structure 6, and the proposed mechanism for its formation. Free-energy profile of the hypothesized [1,5]-sigmatropic hydrogen shift between 7 and 7’, (IEFPCM(CH2Cl2)-M06/6-311++G(2d,2p)//M06/6-31G(d,p) level of theory). Scope of substrates

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

Unusual highly diastereoselective Rh(II)-catalyzed dimerization of 3-diazo-2-arylidenesuccinimides provides access to a new dibenzazulene scaffold

• Anastasia Vepreva,
• Alexander S. Bunev,
• Andrey Yu. Kudinov,
• Grigory Kantin,
• Mikhail Krasavin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2022, 18, 533–538, doi:10.3762/bjoc.18.55

• hydrogen shift. Indene C can either convert into the final indene 3a via a slow 1,3-migration of the hydrogen atom, or is intercepted by carbene A with the formation of cyclopropane D. The relative rates of these competing processes likely determine the composition of the final product mixture. The

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

• -hydrogen shift and σ-bond metathesis with hydrosilane to give the silylated pyrrole product 63 and the LCuH catalyst 57. In addition, the intermediate 58 might go through isomerization to form imine intermediate 64, which undergoes intramolecular cyclization to provide the minor regioisomer 67 (inner cycle

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

• reported that when a polyene 99 or 100 containing an acidic hydrogen in its structure (e.g., a free hydroxy or enol) was subjected to a PET process, the radical cascade was accompanied by a hydrogen shift to give the formal hydroalkylated product 100 or 101 containing a quaternary carbon center (Scheme 38

• reaction was observed in its absence. The authors highlighted the role of the solvent hexafluoro-2-propanol (HFIP) in the stabilization of the radical cation induced by PET and its assistance in the hydrogen shift process. Miscellaneous Lewis acid catalysis in olefin hydroalkylation reactions The ability

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

• undergo a [1,5]-sigmatropic hydrogen shift, to reinstall aromaticity of the indole ring, leading to the formation of 9a. In situ oxidation of intermediates 9a or 9b, probably from the dissolved oxygen present in the reaction mixture, leads to the formation of 1-indolyl-3,5,8-substituted γ-carbolines 3aa

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• carbocation species [52]. Thus, in contrast to the other primary alcohols, an excess of 3.0 equiv was required to provide a moderate 62% yield of mannoside 3g when benzyl alcohol (2g) was used as an acceptor. Next, the formation of tertiary carbenium ion from 3-methyl-butan-2-ol (2i) via 1,2-hydrogen shift in

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• cycloaddition reaction, a retro Diels–Alder reaction of the resulting adduct, and a final 1,3-prototropic hydrogen shift took place to afford cycloadducts 3a,b [55] and 3c–f (87–96% yield) (Scheme 1 and Table 1). As shown by the reaction conditions in Table 1, the reactions of tetrazine derivatives with

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• emerged that the 1,2-hydrogen shift in TS7 is quite high in energy (ΔG‡ = 18.5 kcal⋅mol−1) relative to the previous barriers shown in Figure 2. This barrier is also much higher than the traditional 1,2-hydride shift in carbocations, which usually show barriers even under 10 kcal⋅mol−1. It has been

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• by dehydration. The two tautomers 3/3' would most probably originate by two competitive pathways (a and b; Scheme 4) via a [1,5]-hydrogen shift [28][29]. Hydrogen-bond catalysis promoted by DES components may be playing an important role in favoring the loss of nitrogen under mild conditions from a

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• and then undergoing a 1,5-hydrogen shift with the formation of the colorless ring-closed isomer 9C (Scheme 4, Figure 3). However, the above described rearrangement drastically differs from those previously described due to its very high efficiency. The light-induced formation of the dihydronaphthalene

• electrocyclic reaction followed by the thermally induced 1,5-hydrogen shift reaction. This transformation represents a highly efficient process in comparison with the similar low-efficiency rearrangements of known diphenylmethylene(aryl(hetaryl))fulgides. The key structures of these light-induced reactions – E

Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• the counterclockwise rotation of the isopropyl moiety is necessary for 1,5-hydrogen shift to occur (TS_2-3a in quiannulatene biosynthesis and TS_2-3 in sesterfisherol biosynthesis) [19]. Phase II: conformational changes and hydrogen shifts In phase II, different trends of inherent mobility are seen

• between quiannulatene and sesterfisherol biosynthesis. As shown in Figure 2, C1–C5, C15, C16, C20, and C23 are static, as in phase I. However, C21 is quite mobile, because the C7 carbocation becomes an sp3 carbon due to 1,2-hydrogen shift (TS_4-5). After two successive 1,2-hydrogen shifts, four-step

• . Energy diagram and heat map analysis of conformational change and hydrogen shift (A) IM4–IM6e in quiannulatene biosynthesis. (B) IM5–IM8 in sesterfisherol biosynthesis. An energy diagram and heat map of inherent mobility are shown. All energies are shown in kcal/mol. The Y axis shows the carbon number

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

• Andrew T. King,
• Hugh G. Hiscocks,
• Lidia Matesic,
• Mohan Bhadbhade,
• Roger Bishop and
• Alison T. Ung

Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134

• our compound 5. The formation of compound 8 can be explained by the rearrangement of 7 through a hydrogen-shift to form the diazo intermediate 9 which underwent a concerted [2 + 3] intramolecular cyclisation to 3,3-diphenyl-3H-indazole 8 (Scheme 2). The process was facilitated by the presence of a

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• the enolate intermediate 111 followed by the generation of a C–C bond via conjugate addition delivered intermediate carbene 113. A 1,2-hydrogen shift led to the formation of products 108 with enantioselectivities up to 79% (Scheme 24). Later, Maruoka et al. improved the enantioselectivity up to 95% ee

Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

• Valentin A. Rassadin,
• Mirko Scholz,
• Anastasiia A. Klochkova,
• Armin de Meijere and
• Victor V. Sokolov

Beilstein J. Org. Chem. 2017, 13, 1932–1939, doi:10.3762/bjoc.13.187

• -ortho-quinodimethane derivatives [44], which can rearrange into the corresponding Schiff bases by sigmatropic [1,5]-hydrogen shift [45]. In the case of 13, the extrusion of SO2 must be drastically accelerated due to its carbanionic nature, so that it can occur at 70 °C. The resulting anionic aza-ortho

• -quinodimethane intermediate 14 then, by [1,5]-hydrogen shift gives the ortho-benzylaniline-derived Schiff base 15, which undergoes cyclization to give the indoline derivative 16, and this by subsequent elimination of SO2 and protonation yields 17. The latter, like many indolines [46][47][48] probably is

New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

• Aleksey Yu. Vorob’ev,
• Vyacheslav I. Supranovich,
• Gennady I. Borodkin and
• Vyacheslav G. Shubin

Beilstein J. Org. Chem. 2017, 13, 800–805, doi:10.3762/bjoc.13.80

• 3a -> 2 hydrogen atom migration is a highly exothermic process. However, the formation of 11 is probably kinetically unfavorable due to the prohibited 1,3-hydrogen shift. Thus, no NMR signals corresponding to 11 were found in the reaction mixture before oxidation. Another possible way of deuterium

Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

• Mohammad Haji

Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121

• this reaction, the generated diazomethyl anion 215 underwent a 1,3-dipolar cycloaddition with α,β-unsaturated aldehydes 231 to give pyrazolinecarboxaldehyde 232. The subsequent reaction of aldehyde 232 with another molecule of BOR afforded pyrazoline alkyne intermediate 233 which, after a 1,3-hydrogen

• shift, aromatized to vinylpyrazoles 234. Recently, the [3 + 2] cycloaddition of phosphonate azomethine ylides 235 with ynones 236 to give substituted 1H-pyrrol-2-ylphosphonates 237 has been described by Yu et al. (Scheme 48) [86]. The desired 1H-pyrrol-2-ylphosphonate 241 could also be obtained through

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• result of cascade processes initiated by a thermally activated hydrogen shift. Structurally related fulvenes with non-cyclic acetalic units afforded mixtures of 4- and 9-alkoxybenz[f]indenes under similar thermal conditions. Mechanistic paths promoted by an initial [1,4]-, [1,5]-, [1,7]- or [1,9]-H shift

• rate-determining one and that the [1,9]-H shift is the one with the lowest energy barrier. Keywords: acetal; benzindenes; DFT calculations; fulvene; hydrogen shift; Introduction Fulvenes (also known as pentafulvenes), [1][2][3][4] a unique class of trienes, have intrigued chemists for decades due to

• (Scheme 4). Thus, the different mechanistic paths represented in Scheme 4 for explaining the conversion 3a → 5a + 6a share several common steps, essentially differing in their first hydrogen shift, [1,5]-, [1,7]- or [1,9]-H. Obviously, any attempt to discern which one is the actual reaction path (if only

Synthesis of γ-hydroxypropyl P-chirogenic (±)-phosphorus oxide derivatives by regioselective ring-opening of oxaphospholane 2-oxide precursors

• Iris Binyamin,
• Shoval Meidan-Shani and
• Nissan Ashkenazi

Beilstein J. Org. Chem. 2015, 11, 1332–1339, doi:10.3762/bjoc.11.143

• serve as the catalytic base that prompts the rearrangment. The 1,3-hydrogen shift in a P-propargyl system is well established [51]. In an attempt to prevent this rearrangement we applied an acetylene substituted with the bulky TMS group [58], which may be easily removed at a later stage, and formed the

Hetero-Diels–Alder reactions of hetaryl and aryl thioketones with acetylenic dienophiles

• Grzegorz Mlostoń,
• Paulina Grzelak,
• Maciej Mikina,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2015, 11, 576–582, doi:10.3762/bjoc.11.63

• yielding thiopyran derivatives. The hetero-Diels–Alder reaction occurs in a chemo- and regioselective manner. The initially formed [4 + 2] cycloadducts rearrange via a 1,3-hydrogen shift sequence to give the final products. The latter were smoothly oxidized by treatment with mCPBA to the corresponding

• studies [7][8]. Moreover, thiobenzophenone (1a) was reported to react as a heterodiene smoothly with cyclooctyne, dicyanoacetylene, and dimethyl acetylenedicarboxylate (2a) to give [4 + 2] cycloadducts of type 3a, which spontaneously rearrange via a 1,3-hydrogen shift yielding rearomatized products of

• reaction with dienophiles such as maleic anhydride, acrylonitrile, styrene, and α-chloroacrylonitrile [14][15]. In the latter case, the stabilization of the initially formed cycloadduct occurred via HCl elimination, whereas, in the other cases, the 1,3-hydrogen shift led to rearomatized products. In our

Synthesis of α-amino amidines through molecular iodine-catalyzed three-component coupling of isocyanides, aldehydes and amines

• Praveen Reddy Adiyala,
• D. Chandrasekhar,
• Jeevak Sopanrao Kapure,
• Chada Narsimha Reddy and
• Ram Awatar Maurya

Beilstein J. Org. Chem. 2014, 10, 2065–2070, doi:10.3762/bjoc.10.214

• for the activation of imine. The attack of nucleophilic isocyanide on the activated imine leads to the formation of intermediate 8 or 8’. Subsequently, another molecule of amine attacks the intermediate 8 or 8’ to give α-amino amidine 9 which undergoes further [1,3]-hydrogen shift to provide the α

A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• in-source fragmentation when slightly harsher ionization conditions are used. This fragmentation is in perfect accordance with the zwitterionic iminium structures II’ and III and can also be rationalized for the oxazolidinone alternative II’’, whereas it requires an additional hydrogen shift from the