Asymmetric organocatalytic synthesis of chiral homoallylic amines

• Nikolay S. Kondratyev and
• Andrei V. Malkov

Beilstein J. Org. Chem. 2024, 20, 2349–2377, doi:10.3762/bjoc.20.201

• (producing 106) also showed high enantioselectivity, although the yields varied from modest to good (Scheme 20). Limitations of the scope include the inertness of ketals and methyl dimethoxy acetal (glyoxalic acid derivative) in this reaction. Also, allylation with a simple allyltrimethylsilane failed to

Group 13 exchange and transborylation in catalysis

• Dominic R. Willcox and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28

• gallium hydride, Goicoechea showed the catalytic hydroboration of ketones and CO2 with HBpin. This was also proposed to proceed by carbonyl reduction and Ga‒O/B‒H exchange (Scheme 24c) [116]. Schneider has shown that a mixture of Ga0, AgOTf, and 18-crown-6 catalysed the allylation of acetals, ketals, or

• characterised by X-ray crystallography, lending support to the mechanism proposed by Schneider [118]. Indium catalysis Examples of group 13 exchange are limited with indium, even stoichiometrically [36][45], however Kobayashi demonstrated the InI-catalysed addition of allylic and allenylboranes to ketals

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• groups [98]. In this context, Tan and co-workers succeeded in the enantioselective synthesis of axially chiral SPINOLs 98 from ketals 97 by an intramolecular fashion in the presence of 1 mol % chiral phosphoric acid CPA 22 to afford the axially chiral product (R)-98 in high yield (62–95%) with good to

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

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

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• %, respectively. The conversion of precursors N-sulfinylamino ketone ketals directly to the desired homotropanes represents a four-step intramolecular Mannich cyclization cascade reaction, being the most efficient method to date for the (−)-adaline (1) and (−)-euphococcinine (2) syntheses. Specific rotation was

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• yield (40–86%), with a high selectivity (Scheme 25). As before, a nonphotochemical reaction with Selectfluor® and BEt3 provided a similar selectivity, corroborating the Selectfluor® radical cation as an intermediate and suggesting that an SET mechanism may be possible. 3.3.3 Ketals as directing groups

• : Very recently, Lectka, Dudding and co-workers reported the regioselective C(sp3)–H fluorination of acetonide ketals (Scheme 26A) [205]. C(sp3)–H bonds α to ketal oxygen atoms were fluorinated with surprisingly high selectivity to afford the products 60–63 in moderate to excellent yield (41–91%, Scheme

• from the electrochemical oxidation (Scheme 26C). When the ketals were not fused to a central ring, the least-hindered C(sp3)–H bond reacted, as in the products 61 and 62. When the ketals were fused to a central ring, as in galactose acetonide, the C2 position underwent a selective C(sp3)–H fluorination

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• ketals. The protection of the C-4 hydroxy group, hydrolysis of the acetonide, and selective tosylation of the 1° alcohol were prerequisites for the generation of the C-5–C-6 bond. To this end, the reaction of 82 with the ylide generated from trimethylsulfonium iodide gave the allylic alcohol 83. The

Tuning the stability of alkoxyisopropyl protection groups

• Zehong Liang,
• Henna Koivikko,
• Mikko Oivanen and
• Petri Heinonen

Beilstein J. Org. Chem. 2019, 15, 746–751, doi:10.3762/bjoc.15.70

• applications, where easily cleavable linkers are needed [1]. The stability and properties of acetals/ketals widely varies depending on their structure, which widens the scope of their applicability. The acid lability is increased markedly by attaching electron-donating alkyl groups on the acetal carbon. The

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

• . This spirocyclic functionality is the basic nucleus found in the phorbaketal family of natural products. 5.2. Stereoselective synthesis of chiral spirocyclic ketals Recently, Ishihara and co-workers [126] synthesized chiral C2-symmetric iodoarene 129a and 129b (Figure 3) in few steps and used as

• precatalyst in iodine(III)-catalyzed enantioselective synthesis of spiroketals with high selectivities. In this report, substrates 128 were reacted with 10 mol % of chiral iodoarene 129a and 129b in the presence of mCPBA oxidant in chloroform at 0 °C. The desired ortho-spirocyclic ketals 130 were obtained in

• ortho-substituted phenolic compounds 155 to spiroketals 156 by Quideau and co-workers [139]. The cyclization reactions were performed in trifluoroethanol and spirocyclic ketals 156 were isolated in useful yields (Scheme 58). Additionally, the synthesized spiroketal 156 (R = iPr; R1 = iPr) was used as

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

• M. Fernanda N. N. Carvalho,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

• practical synthetic methods for the selective synthesis of precursor dialkynes bearing different substituents (alkyl, aryl) at the triple bonds, based on ketals or an imine as protecting groups. We show for isomeric dialkynes that the reaction cascade induced by Pt(II) includes ring annulation, sulphur

• as indicated by the arrows in D. Conclusion Several methods for the synthesis of camphor-derived dialkynes having two different alkynyl substituents in close vicinity to each other and to a sulfonamide group were developed. Ketals turned out to be most efficient for the protection of carbonyl groups

A new and expeditious synthesis of all enantiomerically pure stereoisomers of rosaprostol, an antiulcer drug

• Wiesława Perlikowska,
• Remigiusz Żurawiński and
• Marian Mikołajczyk

Beilstein J. Org. Chem. 2016, 12, 2234–2239, doi:10.3762/bjoc.12.215

• afforded diastereoisomeric ketals 2 in ca. 45% yield as a separable mixture. According to this strategy, the starting substrate (−)-2a was converted into (−)-1a in nine steps in 18% overall yield. Then, the C-5 epimeric rosaprostol (−)-1b was prepared from (−)-1a in two steps in 72% yield (Scheme 1). The

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

• Sonia L. Repetto,
• James F. Costello,
• Craig P. Butts,
• Joseph K. W. Lam and
• Norman M. Ratcliffe

Beilstein J. Org. Chem. 2016, 12, 1467–1475, doi:10.3762/bjoc.12.143

• factors which may modulate the rates of hydrolyses. Results and Discussion The ratio of rates corresponding to the hydrolysis of some six-membered ketals and orthoesters were reported previously [18]. Employing a similar approach using the same solvent system (i.e., D2O/CD3CN 1:4 v/v), quantitative rate

• cyclic ketals and orthoesters The ratio of rates for hydrolysis (as opposed to kH+) for 1, 4, 8 and 15 have been reported previously [18]. We prepared 8 and evaluated kH+ using the same conditions employed by these workers to calibrate values of kH+ for 1, 4, and 15 (Figure 1). Acyclic 6 was also

• presented (Figure 1). As anticipated, orthoacetates possessing ethoxy substituents are the most rapidly hydrolysed acyclic systems. Both entropic and steric effects are believed to account for the relatively fast rates of hydrolysis of cyclic orthoesters with respect to ketals. Rate increases within five

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• =O double bond can be converted to ketals, thioketals or even dihalogenomethylenes [1] or react to form hydrazones [2]. On the other hand the C=N double bond can be converted into an oxaziridine group forming chiral oxaziridines which act as enantioselective oxidation reagents [1][3][4][5]. Other

Thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) and complexation with β-cyclodextrin

• Daniel I. Hădărugă,
• Mustafa Ünlüsayin,
• Alexandra T. Gruia,
• Cristina Birău (Mitroi),
• Gerlinde Rusu and
• Nicoleta G. Hădărugă

Beilstein J. Org. Chem. 2016, 12, 179–191, doi:10.3762/bjoc.12.20

• profile of nondegraded and degraded ASO was obtained by GC–MS analysis of the corresponding methyl esters (as well as acetals and ketals of FA degradation compounds). For derivatization, approximately 20 mg of ASO or the corresponding sample was dissolved in 3 mL of boron trifluoride–methanol solution in

Scope and limitations of the dual-gold-catalysed hydrophenoxylation of alkynes

• Adrián Gómez-Suárez,
• Yoshihiro Oonishi,
• Anthony R. Martin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2016, 12, 172–178, doi:10.3762/bjoc.12.19

• as nitriles, ketones, esters, aldehydes, ketals, naphthyls, allyls or polyphenols, in a milder and more efficient manner than the previously reported methodologies. We have also identified that while we are able to use highly steric hindered phenols, small changes on the steric bulk of the alkynes

Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK)

• Pablo Wessig,
• Roswitha Merkel and
• Peter Müller

Beilstein J. Org. Chem. 2015, 11, 74–84, doi:10.3762/bjoc.11.11

• based on spirocyclically joined saturated six-membered rings [8]. The key step of the synthesis of these rods is the formation of ketals and we therefore name this class of compounds oligospiroketals (OSKs). Although the backbone of OSK rods contains many oxygen atoms, these atoms are shielded by

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• )benzene by column chromatography or distillation. Besides, Brønsted acids like trifluoroacetic acid, p-toluenesulfonic acid, that are usually used to generate ketals, or weaker acids like pyridine/hydrogen fluoride led to a side product [35]. The Lewis acid-promoted rearrangement of 1,3-dioxolanyl

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

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

Novel supramolecular affinity materials based on (−)-isosteviol as molecular templates

• Christina Lohoelter,
• Malte Brutschy,
• Daniel Lubczyk and
• Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2013, 9, 2821–2833, doi:10.3762/bjoc.9.317

• particular as templates for tracing air-borne arenes at low concentration. The affinities of the synthesized materials towards different air-borne arenes were determined by 200 MHz quartz crystal microbalances. Keywords: affinity materials; (−)-Isosteviol; supramolecular chemistry; triphenylene ketals

• ][6][7][8][9][10]. Particular interest was given to C3-symmetric structures, serving e.g. as templates in asymmetric catalysis or molecular recognition [11][12][13][14]. A specific but potent subclass of such C3-symmetric architectures is represented by triphenylene ketals [15]. They have found

• [38][39], Within in a nine-step synthesis triphenylene ketals based on (−)-isosteviol were prepared [40]. Receptor structures 2 equipped with amino or sulfonylamido functionalities were obtained (Figure 2). In addition to triphenylene ketals, triptycene-based structures also exhibit the geometrical

Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations

• Götz Bucher,
• Gernot Heitmann and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1668–1676, doi:10.3762/bjoc.9.191

• we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decomposed by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The

• ) should be thermochemically activated (Scheme 2) [22]. To test the above hypothesis, we now investigate the thermochemistry and the photochemistry of the ketals 1 and 3, derived from indan-2-one and ethylene glycol, and cis-2-butene-1,4-diol (Scheme 3). The ketal 2, derived from 1,3-propanediol, was

• chosen as a reference system that cannot undergo a coarctate fragmentation. Results Photolysis and pyrolysis of the ketals. Photolysis (λexc = 254 nm, Hg low-pressure lamp) of indan-2-one ethylene ketal (1), matrix-isolated in Ar at 10 K, leads to the formation of CO2 (vs, ν = 2342.1 cm−1), o-xylylene

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• ], aliphatic acetals and ketals [16], ethers [17], organostannanes [18][19], organosilanes [20][21][22], aromatics [10][23][24], and even alkanes [25][26][27]. BET (path a') could ensue, thus leading to no chemical change. However, when the D–X•+ intermediate contained a good electrofugal group (such as a

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• -diol on one of the alkenes would in principle result in the formation of a cyclic ketal. Spiro and cyclic ketals are ubiquitous in pheromones and in marine natural products [51]. The comparatively long effective lifetime of radicals generated under the conditions of the xanthate transfer may be