(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• alkylation (to 172) were all possible. An alternative pathway to 1,3-cubane 166 was reported by Coote and co-workers (Scheme 17C) [64]. Through their synthesis of enone 176, used in Ueda’s synthesis of cubane 166 and previously only obtained as a side product of the Diels–Alder reaction forming enone 173 [65

• ], they were able to access cubane 166 on gram scale. Synthesis of enone 176 was achieved by a Wharton transposition sequence [66]. The enone 173 was epoxidised yielding epoxide 174, which could be converted into the allylic alcohol 175 by the Wharton reaction. Enone 176 could then be obtained by

• oxidation of alcohol 175 with Dess–Martin periodinane. Synthesis of cubane 166 was then achieved by [2 + 2] cycloaddition of enone 176 using acetone as the photosensitiser (to 177), the first Favorskii ring contraction (to 178), deketalisation, the second Favorskii ring contraction and esterification (to

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• distillation [41]. Under these conditions, exclusive formation of the bis-hydrochlorinated product (not shown) might have been anticipated. Several examples of the hydrochlorination of more complex molecules were reported (Scheme 5). Torii demonstrated the selective formation of chloride 20 when treating enone

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• ]. Two decades later, in 2012 the Overman group demonstrated the utility of this transformation in the total synthesis of (–)-aplyviolene, involving the diastereoselective coupling of a tertiary radical and an enone acceptor [38]. Further developments of this chemistry resulted in the general use of NHPI

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF₃: the case of alkyne hydration. Chemistry vs electrochemistry

• Marta David,
• Elisa Galli,
• Richard C. D. Brown,
• Marta Feroci,
• Fabrizio Vetica and
• Martina Bortolami

Beilstein J. Org. Chem. 2023, 19, 1966–1981, doi:10.3762/bjoc.19.147

• . Hydration of phenylacetylene 1d carried out with 3 equiv of BF3·Et2O for 5 h gave the aldol condensation product 3d (58%) in addition to acetophenone 2d with low yield (32%) (see Table S1, Supporting Information File 1). Assuming that enone 3d is formed from acetophenone, catalysed by the excess Lewis acid

Cyclization of 1-aryl-4,4,4-trichlorobut-2-en-1-ones into 3-trichloromethylindan-1-ones in triflic acid

• Vladislav A. Sokolov,
• Andrei A. Golushko,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2023, 19, 1460–1470, doi:10.3762/bjoc.19.105

• electron-donating substituents in the aromatic ring gave oligomeric materials. Presumably, in these cases, after dehydration and formation of the corresponding enone 2, the latter underwent subsequent cationic oligomerization. Next we studied the intramolecular cyclization of compounds 1 and 2 in TfOH. It

• by X-ray analysis (see Supporting Information File 1). Both, hydroxy ketone 1 and the corresponding enone 2, can be converted into the same indanone 3 in comparable yields; see pairs of reactions for 1a and 2a (indanone 3a), 1d and 2d (indanone 3d), 1i and 3i (indanone 3i), and 1n and 3n (indanone 3n

• in the aryl ring of compound 3k were determined by NOESY correlations between protons in this structure (see Supporting Information File 1). Surprisingly, enone 2j transformed into the phenoxy-substituted indanone 3j in a low yield of 13% (Scheme 5). The formation of the latter represents an

Synthesis of medium and large phostams, phostones, and phostines

• Jiaxi Xu

Beilstein J. Org. Chem. 2023, 19, 687–699, doi:10.3762/bjoc.19.50

• ]. 2.2 Synthesis via [6 + 1] and [7 + 1] annulations The reactions of cyclohex-2-enone (87) and cyclohept-2-enone (88) with dimethyl phosphonate yielded dimethyl bicyclic phostone-phosphonates 89 and 90 under basic conditions in 59% yield via Michael addition, the nucleophilic hydrophosphonylation, and

• intramolecular transesterification. The method was also applied in the derivatization of a steroid derivative 95, affording the corresponding product 96 (Scheme 19) [42]. The reactions are [6 + 1] and [7 + 1] annulations for cyclohex-2-enone and cyclohept-2-enone, respectively. The treatment of (M)-2'-methyl

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• had low ee values, the trans-products showed better enantioselectivities (up to 78%). Their control experiments suggested that the Ru enolate, formed by the conjugate addition of the alkyne to the enone, plays a significant role in the following aldol reaction. Later, Tian et al. have also employed a

• cyclization (Scheme 51A) [93]. The reaction starts with the coordination of the Rh catalyst to the propargyl alcohol 198. In the presence of a base, the rhodium–alkynyl reagent is generated with the concomitant extrusion of benzophenone. Finally, the alkynylation of the enone is followed by the cyclization

• was isolated as the main product (Scheme 52B). Thus far, the direct hydroarylation of such enone-dione substrates was unprecedented, presumably, due to the preferred metal-catalyzed aldol cyclization. Their protocol was further verified by a wide substrate scope. Additionally, the reaction showed high

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

• -hydroboration of the enone 29 with H-B-9-BBN to give an O-B-9-BBN enolate 30. Electrophilic cyanation of the enolate 30 with NCTS 31, and elimination gave the β-ketonitrile 33 and TsN(Ph)-9-B-BBN 34, which underwent B‒N/B‒H transborylation with HBpin to regenerate the catalyst and give TsN(Ph)-Bpin 35 (Scheme 8

• fluoride 50 to give the ester 51 and FBpin (Scheme 11). The H-B-9-BBN-catalysed 1,4-hydroboration of enones with HBpin was shown by Thomas, including the subsequent functionalisation of the intermediate Bpin-enolate 52 (Scheme 12) [76]. The proposed mechanism began by 1,4-hydroboration of the enone 29 with

• reaction of enones and esters or lactones (Scheme 14) [77]. Through a series of single-turnover reactions, a mechanism was proposed (Scheme 14): H-B-9-BBN underwent 1,4-hydroboration with the enone 29, followed by B‒O/B‒H transborylation with HBpin to give an O-Bpin enolate 52 and regenerate H-B-9-BBN

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

• ., compound 122 for further derivatization and structure–activity relationship (SAR) studies [59]. In this case, an intramolecular NHK was carried out on compound 120 prepared from 3-allylcyclopent-2-enone (119) to give the tricyclic compound 121 possessing the eight-membered ring in 73% yield as the major

• Astericus aquaticus (Asteraceae) which possesses a unique backbone featuring a cyclobutane moiety fused to a cyclopentane ring, a γ-lactone, and an eight-membered enone [60][61]. Zhang and Gu achieved its preparation through the use of a late-stage intramolecular NHK reaction (Scheme 23) [62]. Thus, when

An accelerated Rauhut–Currier dimerization enabled the synthesis of (±)-incarvilleatone and anticancer studies

• Tharun K. Kotammagari,
• Sweta Misra,
• Sayantan Paul,
• Sunita Kunte,
• Rajesh G. Gonnade,
• Manas K. Santra and
• Asish K. Bhattacharya

Beilstein J. Org. Chem. 2023, 19, 204–211, doi:10.3762/bjoc.19.19

• accelerate the reaction. In conventional intermolecular RC reactions, the reaction proceeds by the intermolecular addition of a nucleophilic catalyst to the enone substrate to generate an enolate in the first step. In the second step the enolate ion attacks the other Michael acceptor at β-position in an

• addition reaction involved. The low reactivity of intermolecular RC reactions can be improved by incorporating the nucleophilic functionality within a molecule like I (Scheme 1). This nucleophilic functionality present within the enone system first undergoes an intramolecular conjugate addition and is

• functionality (hydroxy group) and an enone system within the same molecule are needed to accelerate the intermolecular RC reaction. Results and Discussion A retrosynthetic plan for the synthesis of (±)-incarvilleatone (1) and (±)-incarviditone (2) is delineated in Scheme 2. We envisaged that both the natural

Sequential hydrozirconation/Pd-catalyzed cross coupling of acyl chlorides towards conjugated (2E,4E)-dienones

• Benedikt Kolb,
• Daniela Silva dos Santos,
• Sanja Krause,
• Anna Zens and
• Sabine Laschat

Beilstein J. Org. Chem. 2023, 19, 176–185, doi:10.3762/bjoc.19.17

• enone building blocks 23 for the synthesis of clifednamides [54][62]. The addition of Schwartz's reagent proceeds as a syn-addition affording (E)-alkenylzirconocenes 24 from terminal alkynes [28]. Based on these precedents from the literature, we surmised that it might be possible to establish a related

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• aromatic common intermediate 9 (Scheme 10). Despite the simplicity, the most obvious disconnections, such as an anionic enone conjugated addition and a direct cationic Friedel–Crafts reaction failed. Highlighting the power of radical disconnection, the group thought of utilizing a β-keto carbon-centered

Synthetic study toward tridachiapyrone B

• Morgan Cormier,
• Florian Hernvann and
• Michaël De Paolis

Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183

• necessary (70% yield, 2:1 dr). The desaturation of the enone compound was next examined and while exposure of 13 to oxidant (o-iodoxybenzoic acid (IBX) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)) left the starting materials unchanged, treatment with NaH in the presence of oxygen to induce the

Total synthesis of grayanane natural products

• Nicolas Fay,
• Rémi Blieck,
• Cyrille Kouklovsky and
• Aurélien de la Torre

Beilstein J. Org. Chem. 2022, 18, 1707–1719, doi:10.3762/bjoc.18.181

• converted to 3 through a 6-step sequence involving reduction of the aromatic ring and oxidation of the enone to a dienone. The resulting dienone 3 underwent a key photoinduced santonin-like rearrangement in the presence of acetic acid, furnishing 4 in high yield. It should be noted that the group of Hiraoka

• enone 10 to the corresponding allylic alcohol, followed by a Au-catalyzed alkyne hydration, providing hemiketal 11. This intermediate was in equilibrium with hydroxy-ketone 12, which was suitable for a SmI2-promoted cyclization, affording intermediate 13 selectively, already bearing rings C and D. The

• with a yield of 26%. The secondary alcohol was protected as a MOM ether and the allylic silyl ether was converted to an enone. A selective oxidative cleavage, only affecting the monosubstituted alkene, led to the formation of 31, which underwent a key SmI2-promoted seven-membered ring closure, giving a

Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• reaction of Meldrum’s acid (26) and aldehyde 27 resulting in the formation of the electron-deficient enone 30, which then participated in a Michael-type addition reaction with 1,3-dipolar 2-unsubstituted imidazole N-oxide 28 to provide the intermediate 31. In the last step, the final product 29 was

Simple synthesis of multi-halogenated alkenes from 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane)

• Yukiko Karuo,
• Atsushi Tarui,
• Kazuyuki Sato,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2022, 18, 1567–1574, doi:10.3762/bjoc.18.167

• , respectively), which are susceptible to basic conditions, were tolerated in the reaction, but ortho substituents hindered the reaction to some extent (Table 2, entries 9 and 10). 2-Hydroxychalcone (3l), which has an electrophilic enone structure, was also tolerated. The Michael addition product was not

A facile approach to spiro[dihydrofuran-2,3'-oxindoles] via formal [4 + 1] annulation reaction of fused 1H-pyrrole-2,3-diones with diazooxindoles

• Pavel A. Topanov,
• Anna A. Maslivets,
• Maksim V. Dmitriev,
• Irina V. Mashevskaya,
• Yurii V. Shklyaev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2022, 18, 1532–1538, doi:10.3762/bjoc.18.162

• compounds to molecules containing an enone fragment. Cycloaddition reactions involving diazo and enone moieties are usually carried out using transition-metal catalysis [18][19][20], with catalyst-free reactions being carried out only with the participation of reactive unsubstituted diazomethane [21][22][23

• ]. With diazooxindoles used as the diazo component, it is possible to obtain the desired spirofuranoxindoles. To date, only one method is known for obtaining spirofuranoxindoles from diazooxindole and an enone, where p-quinone methide acts as the enone, but the reaction requires the use of a catalyst [24

• ] (Scheme 1). Thus, in the present work, we report a simple, catalyst-free diastereoselective method for the synthesis of dihydrofurans spiro-annulated with an oxindole moiety for the first time. The essence of the method is the use of [e]-fused 1H-pyrrole-2,3-diones (FPDs) as the enone component in a

Oxa-Michael-initiated cascade reactions of levoglucosenone

• Julian Klepp,
• Thomas Bousfield,
• Hugh Cummins,
• Sarah V. A.-M. Legendre,
• Jason E. Camp and
• Ben W. Greatrex

Beilstein J. Org. Chem. 2022, 18, 1457–1462, doi:10.3762/bjoc.18.151

• processes in 1, such as the Baylis–Hillman reaction [14], and the Rauhut–Currier reaction which gives dimers such as 2 as well as higher oligomers [10][15]. An oxa-Michael-initiated three-component intermolecular reaction of 1 with furfural and water has been reported to result in enone 3 (Figure 1) [16

• presumed to start with an oxa-Michael initiated aldol reaction promoted by a methoxide nucleophile giving enone 6 via enolate 8 (Scheme 1). A Rauhut–Currier-type reaction of 6 with the addition of another equivalent of 8, followed by a subsequent double β-elimination leads to the observed product 5. When

• formation of 5. Known reactions giving 11, and reactions of dihydrolevoglucosenone 12 and aromatic aldehydes with DBU. Reactions of enone 1 and aldehydes promoted by NaOMe in MeOH. Supporting Information Supporting Information File 323: Experimental details for all compounds including 1H and 13C NMR

Preparation of an advanced intermediate for the synthesis of leustroducsins and phoslactomycins by heterocycloaddition

• Anaïs Rousseau,
• Guillaume Vincent and
• Cyrille Kouklovsky

Beilstein J. Org. Chem. 2022, 18, 1385–1395, doi:10.3762/bjoc.18.143

• -triisopropylsilyloxyhexa-1,3-dien (17): A 0.5 M solution of potassium hexamethyldisilazide in toluene (4.4 mL, 2.22 mmol, 1.2 equiv) was added to a cooled (−78 °C) solution of diethyl chlorophosphate (0.27 mL, 1.85 mmol) in anhydrous THF (7 mL). A solution of the enone 16 (500 mg, 1.85 mmol) in THF (6 mL) was then slowly

Electrochemical hydrogenation of enones using a proton-exchange membrane reactor: selectivity and utility

• Koichi Mitsudo,
• Haruka Inoue,
• Yuta Niki,
• Eisuke Sato and
• Seiji Suga

Beilstein J. Org. Chem. 2022, 18, 1055–1061, doi:10.3762/bjoc.18.107

• proton-exchange membrane reactor is described. The reduction of enones proceeded smoothly under mild conditions to afford ketones or alcohols. The reaction occurred chemoselectively with the use of different cathode catalysts (Pd/C or Ir/C). Keywords: enone; hydrogenation; iridium; palladium; PEM

• the circulating system until 1a was consumed, the ketone 2a, obtained by the exclusive reduction of the C=C moiety, was obtained in 81% yield with a chemoselectivity of 92%. Similarly, cyclopentanone 2b was obtained from the corresponding enone 1b in 74% yield (88% selectivity). Substituted

• . Linear enone 1f gave the desired ketone 2f in high yield (88%, 97% selectivity). Reduction with the PEM reactor also proceeded smoothly with enone 1g, which has a cyclohexene moiety, to give the corresponding ketone 2g in 87% yield (91% selectivity). As shown so far, several kinds of enones 1 could be

Synthetic strategies for the preparation of γ-phostams: 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides

• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 889–915, doi:10.3762/bjoc.18.90

• -enone (160a), and cyclohex-2-enone (160b), all gave the corresponding diastereomeric alkylated products 155–159 and 161–163 (Scheme 26) [52]. By contrast, dinaphth-2-yl-N-benzyl-N-methylphosphinamide (164) generated only the sec-butylated product 165 by the treatment with sec-butyllithium and methanol

Synthesis of odorants in flow and their applications in perfumery

• Merlin Kleoff,
• Paul Kiler and
• Philipp Heretsch

Beilstein J. Org. Chem. 2022, 18, 754–768, doi:10.3762/bjoc.18.76

• of up to 0.35 kg/h for enone 4. In the second step, the obtained 4-aryl-3-buten-2-ones 3 and 4 are selectively hydrogenated in flow using a packed-bed reactor with Raney nickel as catalyst affording raspberry ketone (5) in 91% yield and raspberry ketone methyl ether (6) in 94% yield, respectively

• of hydrogen with a pressure of 1 bar, a good selectivity for the hydrogenation of the external alkene is achieved providing enone 27. The reaction mixture containing enone 27 is then mixed with tosylhydrazone and passed through a column with sulfonic acidic resin Amberlyst-15 to catalyze the

• (34, obtained from castor oil) and benzaldehyde (33). In the industrial process, stoichiometric amounts of sodium- or potassium hydroxide are used resulting in the formation of large quantities of undesired side products, e.g., enone 36, the aldol condensation product of two molecules of heptanal [9

Tri(n-butyl)phosphine-promoted domino reaction for the efficient construction of spiro[cyclohexane-1,3'-indolines] and spiro[indoline-3,2'-furan-3',3''-indolines]

• Hui Zheng,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2022, 18, 669–679, doi:10.3762/bjoc.18.68

• intramolecular addition of the carbanion to the enone affords the cyclic intermediate (C), which in turn converts into the intermediate (D) by transfer of a negative charge. Finally, the spiro compound 3 is formed by elimination of tributylphosphine. When 3-(ethoxycarbonylmethylene)oxindole 4 is employed in the

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• generate the final products 4a–h. Alternatively, nucleophilic attack of hydroxylamine to the carbonyl carbon atom of the enone moiety forms intermediate D. The dehydration of the latter provides oxime E, which through the formation of intermediate F, should be capable to form final product VII. However, as

Solvent-free synthesis of enantioenriched β-silyl nitroalkanes under organocatalytic conditions

• Akhil K. Dubey and
• Raghunath Chowdhury

Beilstein J. Org. Chem. 2021, 17, 2642–2649, doi:10.3762/bjoc.17.177

• the best of our knowledge, organocatalyzed or metal-catalyzed enantioselective conjugate additions of nitroalkanes to β-silyl enones are not yet known. Results and Discussion The optimization study began with the conjugate addition reaction between β-TMS enone 1a and nitromethane (2) as the model

• % yield with 60% ee (Table 1, entry 1). Catalyst II was found to be unproductive as only 25% conversion of β-TMS enone 1a was observed (Table 1, entry 2). Gratifyingly, catalyst III furnished product ent-3a in 85% yield (Table 1, entry 3) with excellent enantioselectivity (94% ee). Whereas catalyst IV

• conditions. The same set of β-silylenones was explored and an almost similar trend in reactivities, yields as well as enantioselectivities was observed. To probe the role of the β-silyl group, the reaction of tert-butyl-substituted enone 3o and nitromethane (2) was conducted under the standard reaction