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

• spongistatin [82]. 2,6-Disubstituted 4-methylenetetrahydropyran was also synthesized from silylstannane and two units of aldehyde in a two-step protocol. The first step involves the addition between silylstannane 185 and an aldehyde in the presence of titanium BINOLate as a catalyst, which afforded

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• graphical format in Figure 2 for the glycolysis reaction of PET, using titanium(IV) n-butoxide as the catalyst. Compared to the uncatalysed process, benefits include milder reaction conditions, higher selectivity and productivity and reduced generation of waste; in short, improved sustainability [84][85

Selective synthesis of α-organylthio esters and α-organylthio ketones from β-keto esters and sodium S-organyl sulfurothioates under basic conditions

• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Thiago Barcellos,
• Claudio C. Silveira and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2021, 17, 234–244, doi:10.3762/bjoc.17.24

• , and related compounds. Some of them are catalyzed by expensive transition metals, such as gold, iridium, palladium, and titanium. More recently, the selective formation of C–S bonds using 1,3-dicarbonyl compounds, followed by a C–C bond cleavage has emerged as a versatile and less expensive protocol

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• reported two types of thiacalix[4]arene-protected titanium–oxo clusters [37]. In that work, p-tert-butylthiacalix[4]arene (H4TC4A) was introduced to tetranuclear and hexanuclear clusters Ti4 and Ti6, respectively (Figure 12). The formed hybrid materials had band gaps of 2.19 eV (Ti4) and 2.24 eV (Ti6). The

• titanium–thiacalix[4]arene-based clusters for H2 evolution, and it also provides a useful method for tuning the band gaps of the catalysts. Apart from reducing the distance between the electron donor and acceptor, calixarenes can also promote the charge separation to enhance the electron transfer [38

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• -unsaturated enone to afford conidiogenone B (171) in 32% yield upon treatment with RhCl3 in microwave. The reaction mechanism of Danheiser’s [3 + 2] annulation is shown according to the Danheiser’s proposal [74] (Scheme 13C, inset). Initial complexation of the α,β-unsaturated ketone 167 and titanium

• cation, which is intercepted by the titanium enolate and results in the new C–C bond formation to give the five-membered carbocycle 169. Conclusion The all-carbon [3 + 2] cycloaddition, together with the [3 + 2] annulation, continue to be an attractive class of reactions for the synthesis of highly

A new method for the synthesis of diamantane by hydroisomerization of binor-S on treatment with sulfuric acid

• Rishat I. Aminov and
• Ravil I. Khusnutdinov

Beilstein J. Org. Chem. 2020, 16, 2534–2539, doi:10.3762/bjoc.16.205

• mL/min)]. The sonication was carried out with an ultrasound generator IL10–0.63 (INLAB LTD) for 180 min at a frequency of 22 kHz with a submerged 15 mm diameter titanium horn, with output power 150 W. The reactions were carried out in a 100 × 35 mm glass reactor equipped with a jacket to maintain the

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• periphery of hierarchically assembled titanium(IV) helicates formed from mixtures of achiral, reactive and chiral, unreactive ligands was investigated in detail. Following the pathway of the chiral induction, the chiral ligands, solvents as well as substituents at the dienophile were carefully varied. Based

• “Werner-type” triscatecholate titanium(IV) complex. Two of these monomers dimerized in a consecutive step to obtain a non-covalently linked helicate (Scheme 1). The dimerization took place via the coordination of three lithium cations acting as bridges between two monomeric complex units [13][14][15][16

• systems possessing catalytic activity with improved solubility. Formation of hierarchically assembled lithium-bridged titanium(IV) helicates as well as the ligands used for the stereoselective Diels–Alder reaction. Previously reported on/off switch for “remote-controlled” [23][24][25][26][27][28][29][30

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• described, including the use of metals other than cobalt (such as rhodium, iridium, titanium, ruthenium, nickel, and palladium), or the use of CO surrogates such as aldehydes, alcohols and formates. Recently, its utility in flow chemistry has also been described [42]. Intramolecular Pauson–Khand reactions

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• photocatalytic decomposition of water on illuminated titanium dioxide (TiO2) electrodes in 1972 [27]. This critical report began the field of semiconductor HPC, and in combination with the development of organic electronics, established fundamental principles that still underpin much of the cutting-edge

• , brookite, and rutile (Figure 3A). The different lattice structures influence the atomic orbital environments and energy, which alters the photophysical and charge transport properties of the material, which has been studied in great detail [78][79][80][81][82]. The titanium and oxygen atomic orbitals

• shown for MnO2 deposited on titanium sheets and nanotubes for photocatalysis [152]. Ray and Lalman deposited nanofiber TiO2 to a metal support via electrospinning a solution of titanium tetraisopropoxide and polyvinyl acetate (PVAc) to form a TiO2-PVAc composite material. TiO2-PVAc was subsequently

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• phosphine with poly(methylhydrosiloxane) in the presence of titanium(IV) isopropoxide (Scheme 4). The work-up of the reaction mixture with 25% HF allowed to remove silicon and titanium impurities and purification of 23 by column chromatography on silica gel yielded the product in 62%. 4

• )isoverbanol (23) Phosphine oxide 22 (0.221 g, 0.6 mmol) was dissolved in dry toluene (2 mL) in a Schlenk flask under nitrogen. Then, poly(methylhydrosiloxane) (PMHS, 0.3 mL) and titanium(IV) isopropoxide (0.672 g, 0.7 mL, 2.4 mmol) were added dropwise to the solution. The reaction mixture was stirred for 24 h

Synthesis of polydicyclopentadiene using the Cp₂TiCl₂/Et₂AlCl catalytic system and thin-layer oxidation of the polymer in air

• Zhargolma B. Bazarova,
• Ludmila S. Soroka,
• Alex A. Lyapkov,
• Мekhman S. Yusubov and
• Francis Verpoort

Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69

• Abstract The polymerization process of dicyclopentadiene using a multicomponent catalytic system based on bis(cyclopentadienyl)titanium dichloride and diethylaluminum chloride was studied. It was demonstrated that the application of an excess of the aluminum component leads to the formation of stable

• through the layers. Consequently, this leads to the transition of the oxidation from a kinetic mode into a diffusive mode. Such structural changes do not occur in a polymer that was stabilized by adding an antioxidant. Keywords: bis(cyclopentadienyl)titanium dichloride; cationic polymerization; oxidation

• hardness of the systems and contributes to the generation of products having a linear structure. To realize this, the usage of a catalyst component bearing already organic ligands in its structure – bis(cyclopentadienyl)titanium dichloride (Cp2TiCl2) is proposed. Polymers based on DCPD, obtained by

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

• of a chiral auxiliary with lithium dibutylcuprate. Next, titanium tetrachloride-catalyzed cyanation secured another carboxy group and after a few transformations an oxazolidinone (4S,5R)-39 was obtained as a major (7:1) product readily purified chromatographically. To complete the synthesis of (2S,3R

• final step transesterification of methyl to benzyl esters was successfully performed in the presence of titanium(IV) benzyloxide to afford dibenzyl esters 102 and 103, respectively. Their hydrogenolysis cleanly produced (2S,3S,4S)-104 and (2S,3S,4S)-105 [103]. From tartaric acids Four-carbon chirons

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• condensation reactions between aldehydes 3 or acetals 5 and ethyl nitroacetate (4). However, the high yield condensations with aldehydes 3 which were reported for some examples [3][4] require more than stoichiometric amounts of titanium tetrachloride thus leading to considerable amounts of metal-containing

• successful. Such phenomenon probably accounts for the modest yields reported in many instances even when using titanium tetrachloride to achieve this condensation [5][6]. Concerning the reduction of the nitroacrylates 2 into the α-nitro esters 6, tangible but still modest yield improvements were observed

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• 1 by replacing reductases with semiconductor photosensitizers and molecular photosensitizers. For example, we reported an ultraviolet-light-driven system using titanium dioxide (TiO2) semiconductor [95][96][97][98][99][100][101]. The conductive band electron of TiO2 (Ered = −0.5 V vs NHE in neutral

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• The first synthesis of diterpenoid eunicellane skeletons incorporating a 1,3-cyclohexadiene moiety is presented. Key step is a low-valent titanium-induced pinacol cyclization that proved to be perfectly diastereoselective. Determination of the relative configuration of the diol was aided by the

• carbinols afforded novel allene systems. Our study may be of help towards the total synthesis of solenopodin or klysimplexin derivatives. Keywords: conformational analysis; low valent titanium; marine natural products; pinacol coupling; ten-membered rings; Introduction Eunicellane-type diterpenoids share

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

• ranged from 67–92%, with enantioselectivities of 21–73% [41]. In 2009, Sun et al. reported heterobimetallic gallium–titanium variations of the same salen complexes as excellent catalysts for the thiolysis and selenolysis of meso-epoxides, giving the desired β-hydroxy sulfides and selenides in near

• ) with MS 4 Å. Asymmetric ring opening of meso-epoxides by p-xylenedithiol catalyzed by a (S,S)-(salen)Cr complex. Desymmetrization of meso-epoxide with thiophenol derivatives. Enantioselective ring-opening reaction of meso-epoxides with ArSH catalyzed by a C2-symmetric chiral bipyridyldiol–titanium

• complex. Enantioselective ring-opening reaction of stilbene oxides with ArSH catalyzed by a C2-symmetric chiral bipyridyldiol–titanium complex. Asymmetric desymmetrization of meso-epoxides using BINOL-based Brønsted acid catalysts. Lithium-BINOL-phosphate-catalyzed desymmetrization of meso-epoxides with

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• aldehydes. While our research was well underway, Ponomarenko and Röschenthaler et al. reported similar Ti(IV)-mediated aldol reactions proceeding via titanium enolates and some succeeding or competing reactions of intermediates or products [34]. Results and Discussion As a model for our investigations we

• reaction (see above), the nucleophilic attack of the silicon enolate (in our case the ketene silylacetal) at the TiCl4-activated aldehyde results in the formation of intermediate 6. Under the influence of the electron-donating substituent, the elimination of titanium oxide dichloride (Ti(O)Cl2) is favored

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• sulfoxide. Different aryl thiols were reacted with aliphatic and aromatic alkenes, showing a reasonable functional group tolerance. In 2015, the group of Greaney substituted the transition metal photocatalysts by titanium dioxide (TiO2) nanoparticles (Scheme 7) [37]. Photoexcitation of electrons to the

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• [CF=CH]-Gly 9, from benzothiazolyl fluoroaminosulfones (Scheme 2) [24][25]. The Julia–Kocienski olefination of 3-alkoxypropanal 7 with phthalimido sulfone 6 afforded the corresponding monofluoroalkene 8 as a (Z):(E) mixture (54:46). Removal of the benzyl group using titanium tetrachloride gave the

Diastereoselective Mannich reactions of pseudo-C₂-symmetric glutarimide with activated imines

• Tatsuya Ishikawa,
• Tomoko Kawasaki-Takasuka,
• Toshio Kubota and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 2473–2477, doi:10.3762/bjoc.13.244

• peaks whose sum is given in parentheses (for example, in the case of entry 3 (Table 1), four small peaks were observed in addition to the major two). It is interesting to note that MHMDS (M: Li or Na) and LDA furnished a different isomer as the major product. We have also prepared the titanium enolate

New bio-nanocomposites based on iron oxides and polysaccharides applied to oxidation and alkylation reactions

• Daily Rodríguez-Padrón,
• Alina M. Balu,
• Antonio A. Romero and
• Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1982–1993, doi:10.3762/bjoc.13.194

• with magnetic properties. Results and Discussion In the present study, we prepared and analyzed three different catalysts based on iron oxides and polysaccharides, in particular: iron oxide–polysaccharide 4 magnetic nanoparticles (Fe2O3-PS4-MNP), iron oxide–polysaccharide 4 (Fe2O3-PS4) and titanium

• ) were generally in good agreement, supporting the validity of our assumption on DMPY adsorbing selectively on Brønsted acid sites. Inductively coupled plasma–mass spectrometry (ICP–MS) The elemental composition of the TiO2-Fe2O3-PS4 material was determined by ICP–MS. The content of iron and titanium was

• 38 and 12 wt %, respectively (Table 3). These values corroborate the incorporation of titanium in the material and confirm the results obtained by XPS. Magnetic susceptibility The magnetic susceptibility of Fe2O3-PS4-MNP is consistent with the XRD data and confirms the magnetic characteristics of the

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

• , titanium-, zirconium-, iron-, cobalt-, vanadium- or aluminum-based Ziegler-type catalysts lead mostly to the linear tail-to-head 2-TH dimer 2,6-dimethyl-1,3,6-octatriene (alloocimene) [27], and the use of nickel catalysts allows the preparation of the tail-to-tail dimer 2-TT (2,7-dimethyl-1,3,7-octatriene

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

Chemical systems, chemical contiguity and the emergence of life

• Terrence P. Kee and
• Pierre-Alain Monnard

Beilstein J. Org. Chem. 2017, 13, 1551–1563, doi:10.3762/bjoc.13.155

• during system preparation was still necessary and it speaks against a separate evolution of the system parts. In the case of fatty acid experiments [90], fatty acid vesicles were formed on/around titanium oxide particles and the irradiation of the photosensitizer powered the reduction of NAD+ to NADH