Chemoenzymatic synthesis of macrocyclic peptides and polyketides via thioesterase-catalyzed macrocyclization

• Senze Qiao,
• Zhongyu Cheng and
• Fuzhuo Li

Beilstein J. Org. Chem. 2024, 20, 721–733, doi:10.3762/bjoc.20.66

• then transformed into aldehyde 31 through several protecting group adjustments and the corresponding alcohol and Ley oxidation. After the preparation of 33 using Evans syn-aldol condensation as a critical step, 34 was produced by thioester formation, desilylation, and allylic oxidation. Incubating 34

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

• the aldol condensation products. Importantly, the ability to recycle the ionic liquid in subsequent reactions was successfully demonstrated. Keywords: alkyne hydration; boron trifluoride; electrochemical synthesis; ionic liquids; Introduction Alkynes are fundamental starting materials towards more

• . 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

• selectively obtained without the aldol condensation products. Considering 4-methylphenylacetylene (1e), the reaction carried out with 3 equiv of BF3·Et2O for 5 h gave only the condensation product 3e (70%, see Table S1, Supporting Information File 1). Reducing the amount of BF3·Et2O to 1 equiv and the

α-(Aminomethyl)acrylates as acceptors in radical–polar crossover 1,4-additions of dialkylzincs: insights into enolate formation and trapping

• Angel Palillero-Cisneros,
• Paola G. Gordillo-Guerra,
• Fernando García-Alvarez,
• Olivier Jackowski,
• Franck Ferreira,
• Fabrice Chemla,
• Joel L. Terán and
• Alejandro Perez-Luna

Beilstein J. Org. Chem. 2023, 19, 1443–1451, doi:10.3762/bjoc.19.103

• protodemetalation to provide ultimately the 1,4-addition adduct. In the presence of carbonyl acceptors, aldol condensation occurs providing overall a tandem 1,4-addition–aldol process. When a tert-butanesulfinyl moiety is present on the nitrogen atom, these electrophilic substitution reactions occur with good

• thus the sense of chiral induction for the 1,4-addition reactions reported in Table 2. Tandem 1,4-addition–aldol condensation reactions We then went on to consider tandem 1,4-addition–aldol condensation reactions (Scheme 6), which offer the interesting prospect of generating an all-carbon quaternary

• informative. As discussed previously (Scheme 4), application of the developed protocol for 1,4-addition to 10 only yields N-benzyl-N-tert-butylsulfinamide following β-elimination. By contrast, in the presence of benzaldehyde, 1,4-addition–aldol condensation is predominant, yielding 26 in 56% yield as a 49:25

Acetaldehyde in the Enders triple cascade reaction via acetaldehyde dimethyl acetal

• Alessandro Brusa,
• Debora Iapadre,
• Maria Edith Casacchia,
• Alessio Carioscia,
• Giuliana Giorgianni,
• Giandomenico Magagnano,
• Fabio Pesciaioli and
• Armando Carlone

Beilstein J. Org. Chem. 2023, 19, 1243–1250, doi:10.3762/bjoc.19.92

• last step involves the enamine intermediate which drives an intramolecular aldol condensation to form the final product 5. In this elegant cascade process, catalyst 1 promotes three consecutive carbon–carbon bond forming steps generating four stereogenic centers with high diastereoselectivity and

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• condensation of intermediate 17 with 2-arylidene-5,5-dimethylcyclohexane-1,3-dione 18 (formed in situ through an Aldol condensation of aldehydes with dimedone), to generate copper(II) benzo[f]chromeno[2,3-h]dihydroquinoxalinoporphyrins which on dehydration produce the desired copper(II) benzo[f]chromeno[2,3-h

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

• (Scheme 47B). The authors concluded that the new structure 186 is formed by intramolecular ring opening of the oxazolidine unit initiated by the hydroxy group either following the aldol condensation or during the reaction workup. In 2021, Zhang and Oestreich presented a Cu-catalyzed tandem conjugate

Rhodium-catalyzed intramolecular reductive aldol-type cyclization: Application for the synthesis of a chiral necic acid lactone

• Motoyuki Isoda,
• Kazuyuki Sato,
• Kenta Kameda,
• Kana Wakabayashi,
• Ryota Sato,
• Hideki Minami,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2022, 18, 1642–1648, doi:10.3762/bjoc.18.176

• aldol reaction is one of the most powerful tools to achieve this transformation [1][2][3][4][5][6][7][8]. In particular, the intramolecular aldol condensation is an important approach to the formation of ring systems such as cyclic β-hydroxy carbonyl products or cyclic α,β-unsaturated carbonyl products

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

• yields (Table 1, entries 5 and 7). Electron-poor aromatic aldehydes including 3-nitrobenzaldehyde and 3-pyridine carboxaldehyde also afforded good yields of the expected products 5g and 5j (Table 1, entries 10 and 13). The reaction of 5-methylfurfural afforded a low yield of 7, and the aldol condensation

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

• ” and only “slightly fruity” [9]. Kappe and co-workers disclosed an access to both odorants in a two-step synthesis (Scheme 1) [24]. In the first step, 4-aryl-3-buten-2-ones 3 and 4 are prepared via aldol condensation of the corresponding aldehydes 1 and 2 and acetone in 78–90% yield with a productivity

• . For compound 6, both individual steps were combined for a two-step aldol condensation/hydrogenation flow sequence providing raspberry ketone methyl ether (6) on a gram scale in 75% overall yield. Interestingly, also alternative flow protocols for the synthesis of 4-aryl-3-buten-2-ones 3 and 4 were

• extensively in perfumes” and “soap perfumes” to introduce “jasmine-like floralcy when accompanied by more volatile chemicals of floral character”, while assisting “in fixation of the fragrance” due to its relatively high boiling point of 285 °C. It is industrially produced by an aldol condensation of heptanal

Tosylhydrazine-promoted self-conjugate reduction–Michael/aldol reaction of 3-phenacylideneoxindoles towards dispirocyclopentanebisoxindole derivatives

• Sayan Pramanik and
• Chhanda Mukhopadhyay

Beilstein J. Org. Chem. 2022, 18, 469–478, doi:10.3762/bjoc.18.49

• Michael addition with another molecule of 3-phenacylidieneoxindole to yield intermediate B. Finally, an intramolecular aldol condensation takes place between the carbanion and the carbonyl group of intermediate B towards the formation of the dispirocyclopentanebisoxindole derivative. To support the

• cyclization of two molecules of 3-phenacylideneoxindoles. In this reaction tosylhydrazine serves as reducing agent to reduce one molecule of 3-phenacylideneoxindole to 3-phenacylindolinone which, under base-catalyzed conditions, involves a sequential Michael addition/intramolecular aldol condensation with

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• occurred via an aza-Michael/aldol condensation/vinylogous Michael addition/aldol condensation sequence (Table 26) [67]. Recently, the synthesis of axially chiral 4-naphthylquinoline-3-carbaldehydes 117 has been reported via Michael/Aldol cascade reaction of alkynals 116 with N-(2-(1-naphthoyl)phenyl

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

• applied on terpenoids are abundant in the literature. As terpenoids are one of the most important odorants in the F&F industry. Schütz et al. developed an aldol condensation of citral (79, 63:37 mixture of geranial (Z)-79/neral (E)-79) with acetone to prepare ψ-Ionone or pseudoionone (80) in good yield

• process. A recent example, Gavriilidis et al. described a heterogeneous version for the synthesis of 4-(4-methoxyphenyl)butan-2-one (85) starting from 4-methoxybenzyl alcohol (84). In this case, the preparation is divided in 3 stages: oxidation, aldol condensation, and reduction (Scheme 16). The setup

Synthesis of functionalized imidazo[4,5-e]thiazolo[3,2-b]triazines by condensation of imidazo[4,5-e]triazinethiones with DMAD or DEAD and rearrangement to imidazo[4,5-e]thiazolo[2,3-c]triazines

• Alexei N. Izmest’ev,
• Dmitry B. Vinogradov,
• Natalya G. Kolotyrkina,
• Angelina N. Kravchenko and
• Galina A. Gazieva

Beilstein J. Org. Chem. 2021, 17, 1141–1148, doi:10.3762/bjoc.17.87

• 4c–g,j–n bearing phenyl substituents contained no impurities of the corresponding isomers 5, while the structures 4a,b,h,i were isolated in individual form only during fractional crystallization from the reaction mixtures. It was previously shown [24][25][26] that the products of aldol condensation

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

• aldol condensation [36]. The catalytic system for this transformation was adapted from earlier works [34][36] and included the addition of a 42% aqueous solution of HBF4 that facilitated consequent cyclization. A series of various β-(2-acylphenyl)enones and arylboronic acids was tested. Almost every

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

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

• oxidation of (Z)-15a followed by immediate aldol condensation afforded racemic phenol ester (rac)-17 via aldehyde 16. However, several attempts to form enantioenriched aldol fragment 18 using both a chiral auxiliary [25][26][27][28] and catalytic asymmetric [29][30] procedures proceeded without success

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

• later stage of the synthesis without the need of pre-installation of necessary functional groups as a reaction precursor, for instance, ring-closing metathesis, intramolecular aldol condensation, and others. One major issue that still needs to be addressed is the selectivity of the all carbon [3 + 2

Recent synthesis of thietanes

• Jiaxi Xu

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

• double displacement with sodium sulfide to obtain thietane-3,3-diyldimethanol (13), which was further converted into two different thietanose nucleosides 2 and 14 [33] (Scheme 2). In the synthesis of sesquiterpene thioalkaloids, the method also was utilized. A double-aldol condensation of methyl

A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes

• Dragana Vuk,
• Irena Škorić,
• Valentina Milašinović,
• Krešimir Molčanov and
• Željko Marinić

Beilstein J. Org. Chem. 2020, 16, 1092–1099, doi:10.3762/bjoc.16.96

• 54, 10000 Zagreb, Croatia NMR Centre, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia 10.3762/bjoc.16.96 Abstract In order to prepare novel polycyclic derivatives of bicyclo[3.2.1]octadiene systems fused with a thiophene ring, photochemical cyclization and aldol condensation

• of the substituent could be seen through a shift of the aromatic singlet, which is, in the case of methoxy-substituted derivative 9, shifted downfield, due to the electronic and anisotropic effect of the methoxy group. In continuation of the study herein presented, the aldol condensation reaction of

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• can support removal of this substituent altogether, with only small potency loss (HITub-7) [20]. The progression and results of this SAR study are explained below in the section on bioactivity. General synthetic access Synthetic routes to HTIs are well established [26] and typically involve aldol

• condensation of benzaldehyde onto thioindoxyls. However, the key step is the formation (and where necessary, isolation) of the thioindoxyl species. In our studies, the electron-rich dimethoxy- and trimethoxy-substituted thioindoxyls were noted to be unstable to air, base, and silica gel during chromatography

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• the phenyl ring was performed through the aldol condensation of indoxyl-3-acetate with the corresponding benzaldehydes under alkaline conditions (Scheme 1) [13]. All compounds 1a–c were obtained in good yields as pure Z-isomers as supported by the NMR data (Figures S5–S13 in Supporting Information

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• ]. Oxidation, iodocarboxylation and elimination yielded the lactone 43. A series of functional group manipulations provided enone 44, which underwent a cuprate-mediated Michael addition and liberation of the aldehyde 46 upon ozonolysis. After intramolecular aldol condensation the resulting enone 47 was

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• carried out in many research groups. The first racemic total synthesis of triptolide was reported 1980 by Berchtold and co-workers (Figure 2, route A, and Scheme 1) [66]. The key steps include: i) construction of the A-ring by aldol condensation, ii) construction of the butenolide (D-ring) by acid

• diastereomeric amides 39. Collins oxidation of 39 gave an aldehyde intermediate, which subsequently subjected to an aldol condensation using a ten-fold weight excess of neutral alumina quantitatively provided 40 and 41 in a small-scale reaction. The yield varied in large-scale reactions mainly due to the

• afforded triptolide (1, 21%) and 14-epitriptolide (48, 68%). Overall, the first total synthesis of racemic triptolide was finished from tetralone 22 in 16 steps. Although the intractable problems in some transformations, such as the neutral alumina-mediated aldol condensation to produce 40 and 41, the

Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum

• Jan Rinkel,
• Alexander Babczyk,
• Tao Wang,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277

• tetraketide intermediate that can be cyclised by aldol condensation, followed by elimination of water to result in the aromatic ring system. Thioester hydrolysis and decarboxylation produce 29a that can be converted by SAM-dependent O-methylation into 24. In summary, this hypothetical biosynthetic mechanism

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

• p-ethoxybenzaldehydes led selectively to aldol condensation products with (E)-configured double bonds in 30–40% yields. In preliminary experiments with an SF5-substituted acetic acid morpholide and p-nitrobenzaldehyde, a low amount of an aldol product was formed under similar conditions. Keywords

• (Table 2, entries 1–6). In contrast, from the reactions of 1 with benzaldehydes bearing electron-donating substituents (methyl-, methoxy-, ethoxy-) no aldol addition products could be isolated (Table 2, entries 7–9), but the aldol condensation products 4g–i were isolated in fair yields (see below). On

• state A are the major products of the aldol addition reactions. As mentioned above, aldol addition products were not isolated from the reaction of 1 with electron rich p-methyl-, p-methoxy-, and p-ethoxybenzaldehydes. Here, aldol condensation products 4g–i were obtained as single isomers after

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

• Jun Ki Kim,
• Hwan Jung Lim,
• Kyung Chae Jeong and
• Seong Jun Park

Beilstein J. Org. Chem. 2018, 14, 243–252, doi:10.3762/bjoc.14.16

• ,S-acetals 9a–c since the X-ray crystal structure of Meldrum’s acid-based N,S-acetal was reported by Wentrup [84]. In addition, the intramolecular aldol condensation of Meldrum’s acids did not occur due to the ketone structures. Table 2 displays the 1H NMR result of the sulfur ylide-like intermediate

• methanimidothioate 7ao, and time dependent experiments of the intramolecular aldol condensation of N,S-acetal 7aa to 8aa in N,N-dimethylformamide-d7 at room temperature confirmed the formation of the stable sulfur ylide-like intermediates, thus indicating the successful transformation into thiophenes 8an, 8ao, and