C–H Trifluoromethylthiolation of aldehyde hydrazones

• Victor Levet,
• Balu Ramesh,
• Congyang Wang and
• Tatiana Besset

Beilstein J. Org. Chem. 2024, 20, 2883–2890, doi:10.3762/bjoc.20.242

• cyclization of aryl hydrazones with aryl isothiocyanates promoted by elemental sulfur [70]. In the course of their studies for the thiocyanation of ketene dithioacetals, Yang, Wang and co-workers developed an electrochemical oxidization-based synthetic strategy to circumvent the need for external oxidants. In

Transition-metal-free decarbonylation–oxidation of 3-arylbenzofuran-2(3H)-ones: access to 2-hydroxybenzophenones

• Bhaskar B. Dhotare,
• Seema V. Kanojia,
• Chahna K. Sakhiya,
• Amey Wadawale and
• Dibakar Goswami

Beilstein J. Org. Chem. 2024, 20, 2655–2667, doi:10.3762/bjoc.20.223

• environmental hazards, and this can only be circumvented using a transition-metal-free synthesis protocol. Although eco-friendly methods for the synthesis of 2-hydroxybenzophenones have been reported via a cycloaromatization of α-alkenoyl ketene dithioacetals and nitroethane in water [15], an alternate and more

Stereoselective mechanochemical synthesis of thiomalonate Michael adducts via iminium catalysis by chiral primary amines

• Michał Błauciak,
• Dominika Andrzejczyk,
• Błażej Dziuk and
• Rafał Kowalczyk

Beilstein J. Org. Chem. 2024, 20, 2313–2322, doi:10.3762/bjoc.20.198

• adduct. Hence, after 24 hours up to 9% of sulfa-adduct was formed (see Supporting Information File 1 for details). Unfavorable in this case is the formation of ketene via thiol elimination [40], leading to the formation of a mixture of products where the thia-Michael adduct predominates over the desired

Selective hydrolysis of α-oxo ketene N,S-acetals in water: switchable aqueous synthesis of β-keto thioesters and β-keto amides

• Haifeng Yu,
• Wanting Zhang,
• Xuejing Cui,
• Zida Liu,
• Xifu Zhang and
• Xiaobo Zhao

Beilstein J. Org. Chem. 2024, 20, 2225–2233, doi:10.3762/bjoc.20.190

• Haifeng Yu Wanting Zhang Xuejing Cui Zida Liu Xifu Zhang Xiaobo Zhao College of Chemistry, Baicheng Normal University, Baicheng, Jilin 137000, China 10.3762/bjoc.20.190 Abstract An eco-friendly selective hydrolysis of chain α-oxo ketene N,S-acetals in water for the switchable synthesis of β-keto

• thioesters and β-keto amides is reported. In refluxing water, the hydrolysis reactions of α-oxo ketene N,S-acetals in the presence of 1.0 equiv of dodecylbenzenesulfonic acid effectively afforded β-keto thioesters in excellent yield, while β-keto amides were successfully obtained in excellent yield when the

• hydrolysis reactions were carried out in the presence of 3.0 equiv of NaOH. The green approach to β-keto thioesters and β-keto amides avoids the use of harmful organic solvents, thiols and thiolacetates as well as amines, which could result in serious environmental and safety issues. Keywords: α-oxo ketene

Efficacy of radical reactions of isocyanides with heteroatom radicals in organic synthesis

• Akiya Ogawa and
• Yuki Yamamoto

Beilstein J. Org. Chem. 2024, 20, 2114–2128, doi:10.3762/bjoc.20.182

• lack of geometrical isomerization of the C–N double bond of the dithiolation products [32]. The thioselenation product 6’, an imine derivative, can be converted to a β-lactam derivative by [2 + 2] cycloaddition with ketene generated in situ. For example, thioselenation of RNC (R = (EtO)2P(O)–CH2) gave

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

• -unsaturated ketones 98 are S,S-ketene acetals capable of undergoing Liebeskind–Srogl coupling with boronic acids and phenylhydrazine in a consecutive three-component reaction to give pyrazoles 99 (Scheme 35) [118]. Beltrán-Rodil et al. used a similar strategy to synthesize 1,3,5-substituted pyrazoles 101 by

Harnessing the versatility of hydrazones through electrosynthetic oxidative transformations

• Aurélie Claraz

Beilstein J. Org. Chem. 2024, 20, 1988–2004, doi:10.3762/bjoc.20.175

• thiocyanation of ketene dithioacetals, Wang and Yang et al. mentioned one example of thiocyanation of benzaldehyde-derived hydrazone 120 using potassium thiocyanate as a source of thiocyanate radical. The electrolysis was conducted in the presence of two equivalents of water in acetonitrile with lithium

Access to 2-oxoazetidine-3-carboxylic acid derivatives via thermal microwave-assisted Wolff rearrangement of 3-diazotetramic acids in the presence of nucleophiles

• Ivan Lyutin,
• Vasilisa Krivovicheva,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 1894–1899, doi:10.3762/bjoc.20.164

• -generated ketene, previously described using carbocyclic diazodiketones [35] were also unsuccessful. Of the diazotetramic acids, only the spiro adamantane derivative 1m was not able to form the desired β-lactam. These reactions gave complex mixtures of unidentified products. The benzyl esters 3k and 3n were

• the exocyclic carbonyl group by preformed ring contraction and interaction of the intermediate ketene with the selected nucleophile. Various aromatic and aliphatic amines as well as alcohols and thiols can be used as nucleophiles. 5-Monosubstituted diazotetramic acids give exclusively trans

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• of polarized ketene-N,O-acetal to the alkyne β-carbon and trapping of the sulfonium cation at the alkyne-α-carbon afforded 5-(arylthio)-3,6-dihydropyridin-2(1H)-one 148. The coordination of a sulfonium electrophile to the C–C triple bond of 1-I occurred through cyclopropyl intermediate 1-I. The

Synthesis of ether lipids: natural compounds and analogues

• Marco Antônio G. B. Gomes,
• Alicia Bauduin,
• Chloé Le Roux,
• Romain Fouinneteau,
• Wilfried Berthe,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2023, 19, 1299–1369, doi:10.3762/bjoc.19.96

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• coupling process. Initially, ether 64 interacts with tert-butoxyl radicals via hydrogen atom transfer reaction to generate radical A with release of tert-butyl alcohol. Subsequently, the radical A adds to the C=C bond of α-oxo ketene dithioacetal 107 to form radical B, which further reacts with Fe(III) to

Asymmetric tandem conjugate addition and reaction with carbocations on acylimidazole Michael acceptors

• Brigita Mudráková,
• Renata Marcia de Figueiredo,
• Jean-Marc Campagne and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 881–888, doi:10.3762/bjoc.19.65

• enolates obtained from acylimidazoles in this work with other metal enolates obtained by related conjugate additions. In comparison, the HOMO energy of a related silyl ketene aminal was similar (−7.87 eV) but its NBO charge was more negative −0.343. The TMS enolate of benzoxazole has a higher HOMO energy

Vicinal ketoesters – key intermediates in the total synthesis of natural products

• Marc Paul Beller and
• Ulrich Koert

Beilstein J. Org. Chem. 2022, 18, 1236–1248, doi:10.3762/bjoc.18.129

• cycloisomerization of the α-ketoester 22, which can be described as a Friedel–Crafts-type reaction or an aldol reaction of an S,O-ketene acetal (Scheme 4). The required ketoester 22 was synthesized from sulfonylchromenone 20, accessible from dihydroxyacetophenone 19 and thiol 18 derived from known alcohol 17 [11][12

• (−)-irofulven (87), Movassaghi et al. used a CuII-catalyzed asymmetric aldol reaction of O-silyl ketene S,O-acetal 84 with methyl pyruvate (85) to enantioselectively install the crucial tertiary TMS-protected alcohol in ester 86 (Scheme 14) [29]. Eleven further steps gave (−)-irofulven (87). 2. Mesoxalic

Syntheses of novel pyridine-based low-molecular-weight luminogens possessing aggregation-induced emission enhancement (AIEE) properties

• Masayori Hagimori,
• Tatsusada Yoshida,
• Yasuhisa Nishimura,
• Yukiko Ogawa and
• Keitaro Tanaka

Beilstein J. Org. Chem. 2022, 18, 580–587, doi:10.3762/bjoc.18.60

• -yl)amino)-substituted maleimides. Results and Discussion Maleimides are versatile reagents for the synthesis of heterocyclic compounds. Previously, we have reported functional maleimides derived from ketene dithioacetals and have prepared fluorescent compounds using this reagent [23][24]. In this

Tenacibactins K–M, cytotoxic siderophores from a coral-associated gliding bacterium of the genus Tenacibaculum

• Yasuhiro Igarashi,
• Yiwei Ge,
• Tao Zhou,
• Amit Raj Sharma,
• Enjuro Harunari,
• Naoya Oku and
• Agus Trianto

Beilstein J. Org. Chem. 2022, 18, 110–119, doi:10.3762/bjoc.18.12

• conducted [24] (Figure 4). In the negative ion mode, a precursor ion m/z 654 underwent sequential eliminations at every hydroxamate C–N bond, giving rise to ketene-terminated product ions at m/z 621 and 421, which supported the position of hydroxylation at N37 and N26 and chain lengths of each cadaverine

• /succinic acid module (Scheme 1, paths E1 and E2). The third elimination product, C15-ketene (structure in square brackets, Scheme 1) was not observed, but a pentadecenoate anion, appearing at m/z 239, warranted the existence of fragmentation path E3 and also the chain length of the acyl unit. Hydration of

• ketene to give carboxylate was also detected as an ion at m/z 439. The fragment ions m/z 232, 199, 181, and 98 were commonly detected in the MS/MS spectra for compounds 1–3, which appeared to be derived from the right half of the molecule by sequentially losing hydroxyamine, water, and tetrahydropyridine

Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

• Yelong Lei and
• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 70–76, doi:10.3762/bjoc.18.6

• -2-yl)alkanamides and 1-(oxazolin-2-yl)alkylphosphonates. Keywords: aziridine; diazooxoester; diazo compound; ketene; oxazoline; ring expansion; Introduction Oxazoline derivatives are an important class of nitrogen and oxygen-containing five-membered unsaturated heterocycles [1] and widely exist in

• heating, diazo esters 1 undergo a Wolff rearrangement to generate ethoxycarbonylketenes A by loss of nitrogen. The nucleophilic attack of 2-arylaziridine 2 on the ketene moiety produces zwitterionic intermediates B, in which the aziridinium is opened to form the benzylic carbocation stabilized through the

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• ion pair with the chloride of the N-acyl(iso)quinolinium intermediate II. Hence, the reaction would follow a SN1-type mechanism via anion-binding catalysis. In Jacobsen’s report, the acylating agent 2,2,2-trichloroethyl chloroformate (TrocCl) and nucleophilic silyl ketene acetals were employed to

• ][75][76]. For this purpose, based on their initial findings in 2008 [38], the enantioselective addition of silyl ketene acetals to racemic 1-chloroisochromane (73) was more closely examined (Scheme 16) [73][74][75][76]. In this type of reaction, thiourea catalyst 76 actively engages in the ionization

• enantioselectivity, but the catalyst itself accommodates the anion by adopting a helical conformation upon complexation (Scheme 18a) [84][85][86]. Initial studies proved these systems highly effective for the enantioselective Reissert reaction of quinolines with silyl ketene acetals [22], which could be later

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

• cyclic ketene acetals [277]. This copolymer also showed a well-controllable reversible UCST behavior in aqueous solutions. In 2020, Zhao et al. reported that by incorporating azobenzene functionalities into polyacrylamide copolymers, the responsive UCST behavior was furthermore tuneable via light

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• hydrogen atoms from thiophenol to produce the final product 47 (Scheme 17). In 2020, Alemán and colleagues [53] proposed an approach in which ketene 48 and diene 49 condense with the help of diamine 51 to afford cyclobutane product 50 (Scheme 18). The reaction could be catalyzed by a simple diamine due to

• enantiomer to diastereomer. A plausible mechanism is shown in Scheme 19. In the presence of acid, EDA complex 52 is formed by ketene 48 and diamine 51. Then, the ground state 52 transforms into excited state 53 or into unproductive charge-transfer excited state 54 that can restore ground state 52 by BET

• , promoted by irradiation with visible light. In 2017, Shirke and Ramaastry [40] proposed an organic catalyzed β-azide reaction of ketene 155 initiated by the EDA complex formed by DABCO and Zhdankin reagent 156 (Scheme 54). A variety of β-azidoketones was conveniently obtained with good to excellent yield

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• . J. K. Taylor and co-workers reported the first total synthesis of inthomycin B ((+)-2) using a Stille coupling of a stannyl-diene with an oxazole vinyl iodide unit followed by a Kiyooka ketene acetal/amino acid-derived oxazaborolidinone procedure as its cornerstones (Scheme 4) [43]. In the beginning

• (Z,E)-52 with silyl ketene acetal 53 in the presence of oxazaborolidinone derived from N-tosyl-ʟ-valine and BH3·THF generated the desired alcohol (Z,E)-(+)-54 in 74% yield and 64% ee. Next, a wide range of catalysts/conditions were screened for the crucial Stille coupling between iodide 48 and (Z,E

• asymmetric aldol reaction in the presence of oxazaborolidinone derivative 68 and silyl ketene acetal 53 to produce the required α-hydroxy ester (+)-11 in 50% yield and 76% ee ((R)-stereochemistry of the major enantiomer). A competitive reduction of 71 was also observed to produce alcohol 72 in 43% yield

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• position; ketene; mixed chromophores; Introduction Enones exhibit a rich and diverse photochemistry. The deep-seated photochemical rearrangements found in these systems have attracted numerous mechanistic studies. In this context, the photochemistry of α,β-enones A and β,γ-enones B (Figure 1) has become

• , the photorearrangement route is selectively from the α,β-enone part and we confirmed that the irradiation follows a type B rearrangement (Scheme 2) [16]. Another interesting set of competitive 1,5-(C–O) acyl shift rearrangements (formation of vinyl ketene) with that of 1,2-AS were observed when

• ]. Photoreaction of 7a and 7b Irradiation of a degassed solution of 7a,b in benzene at 254 nm for 3–4 h yielded a pale yellow solid of ketene 10a,b (Scheme 5, Table 2) through regioselective photoinduced 1,5-phenyl migration and we did not obtain any 1,2-AS or any other photoproduct. The same ketenes were isolated

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

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

• iodine-catalyzed Mukiyama–Michael addition of the ketene silyl acetal 104 to 103 afforded the trans-1,5-disubstituted tetrahydropyranone 105. After the generation of the C-3-exocyclic olefin and functional group manipulation, the Takai olefination [40] of the aldehyde 106 gave the trans-vinyl iodide 107

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• ) with alkenes worked as well [73]. In 1987, Ooms and Hartmann showed the photochemical [2 + 2] cycloaddition of diaryl thione 184b with ketene acetals 247 [74] (Scheme 48). In the same year, Nishio studied the photocycloadditions of nitrogen-containing cyclic thiones 249 and 250 with 2