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Search for "cyclisation" in Full Text gives 174 result(s) in Beilstein Journal of Organic Chemistry.
Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate
Beilstein J. Org. Chem. 2020, 16, 2108–2118, doi:10.3762/bjoc.16.178
- give the intermediate A which undergoes homolytic cleavage yielding B. Subsequent cyclisation results in the oxazole ring. During these optimization trials, it was interesting to note the formation of 2-aminothiazole, when ferric chloride was employed along with thiocyanate (Table 1, entry 3). There is
The biomimetic synthesis of balsaminone A and ellagic acid via oxidative dimerization
Beilstein J. Org. Chem. 2020, 16, 2026–2031, doi:10.3762/bjoc.16.169
- previous synthesis of balsaminone A (4) [22] (Scheme 3), silver oxide was used as the oxidative dimerizing agent for the formation of the binaphthoquinone intermediate 13. This was followed by photolytic cyclisation and ortho-formylation to give carbaldehyde 14. Conversion to balsaminone A (4) could then
Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts
Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130
- hydroxy moiety at the carbonyl carbon of IIIb further drove the cyclisation to afford the bromomethylcoumarin 4a. Conclusion In summary, we reported the first protocol on the quaternary phosphonium salt-mediated direct synthesis of cinnamyltriazoles and 3-(bromomethyl)coumarins from Morita–Baylis–Hillman
Heterogeneous photocatalysis in flow chemical reactors
Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125
- to fuse samarium oxide nanoparticles to TiO2 and ceria (CeO2) as a bifunctional heterogeneous photoredox Lewis acid catalyst for reductive cyclisation reactions, previously reported with ruthenium transition metal complex photocatalysts [157]. Both electrochemical and photochemical deposition
Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo
Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14
- , lithium diisopropylamide (LDA)-mediated cyclisation of 2-(methylthio)benzamides, which were obtained by directed ortho-metalation of the respective benzamides followed by quenching with dimethyl disulfide [27] (Supporting Information File 1, Scheme S1). In general, we found the LDA-mediated cyclisation
Terpenes
Beilstein J. Org. Chem. 2019, 15, 2966–2967, doi:10.3762/bjoc.15.292
- generate a highly reactive cationic intermediate that can be subject to a cascade reaction through typical carbocation chemistry, including cyclisation reactions, hydride migrations and Wagner–Meerwein rearrangements [1][2]. The cascade is usually terminated by deprotonation or attack of water. The
Nanangenines: drimane sesquiterpenoids as the dominant metabolite cohort of a novel Australian fungus, Aspergillus nanangensis
Beilstein J. Org. Chem. 2019, 15, 2631–2643, doi:10.3762/bjoc.15.256
- [33][34][35]. Specifically, AstC contains a DxDTT motif [21], which is a variant of the DxDD motif known to be involved in class II-type protonation-initiated terpene cyclisation [36]. Importantly, the DDxxD motif in AstC contains a substitution of the second Asp for Asn, leading to a loss of
- ionisation-activated cyclisation activity. Two other HAD-like hydrolases, AstI and AstK, with the class I (DDxxD/E) motif, are therefore required to catalyse other dephosphorylation steps. Despite overall low sequence homology, alignment with the amino acid sequences of AstC, AstI, AstK and related homologs
- FE257_006542 contains both class I (DDxxD/E) and class II (DxDD, QW) terpene synthases, we propose that FE257_006542 is responsible for both the cyclisation into drimanyl diphosphate and the hydrolysis of the diphosphate into drim-8-ene-11-ol. We propose the next step in the pathway is hydroxylation at C-6 or
Synthetic terpenoids in the world of fragrances: Iso E Super® is the showcase
Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252
- ) (Scheme 3) [17][18][19][20][21]. To produce Ambrelux (32), myrcene (1) is reacted with dienophile (31) in a Diels–Alder cycloaddition promoted under Lewis-acidic conditions. In order to obtain Iso E Super® (33), Brønstedt acid-mediated cyclisation, similar to the one utilised for the first synthesis of
- ionone (30), proved feasible on large scale. As it turned out, not only the one depicted, but several other cyclisation products formed. The main constituent was Iso E Super® (33). A minor byproduct is now referred to as Iso E Super Plus® (34, Scheme 4). Small modifications of the reaction conditions
- conditions for the synthesis of all Iso E Super® related compounds vary slightly. The main difference lies in a prolonged isomerisation process of the Diels–Alder product 32 before and after the second cyclisation step. Georgywood® (35) named after Georg Fráter is industrially produced with, e.g., methanol
Effect of ring size on photoisomerization properties of stiff stilbene macrocycles
Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233
- gaining popularity as a unit in molecular machines and photodynamic systems a clear understanding of the effect of cyclisation on the photoisomerization is of general interest. Experimental Starting materials, solvents and reagents were commercially available and used without further purification except
Harnessing enzyme plasticity for the synthesis of oxygenated sesquiterpenoids
Beilstein J. Org. Chem. 2019, 15, 2184–2190, doi:10.3762/bjoc.15.215
- substrates, thereby opening up direct and efficient synthetic routes to oxidised sesquiterpenoids. This represents in essence a reversal of the biosynthetic pathways to oxidised sesquiterpenoids since cyclisation occurs after FDP ‘oxidation’. 8-Methoxy-FDP (11) and 12-methoxy-FDP (12) were both prepared in
- = 5.17, t, JH,H = 7.0 Hz) due to the presence of the methoxy group two carbon atoms away. The ADS-catalysed 1,11-cyclisation of diphosphate 11 suggests that the 8-methoxy group prevents the formation of a conformation conducive to isomerisation to NDP (4, Scheme 1) and hence 1,6-cyclisation to generate a
- bisabolyl cation and the amorphane skeleton. Rather the active site conformations of 11 and cation 22 appear to enable a 1,11-cyclisation to 23. A subsequent [1,3]-hydride shift to cation 24 and deprotonation from C15 lead to 8-methoxy-γ-humulene (20, Scheme 3A). Alternatively, the nucleophilic 8-methoxy
1,2,3-Triazolium macrocycles in supramolecular chemistry
Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211
- -triazolium receptors A ferrocene-containing dicationic bis-triazolium macrocycle 4 (see Figure 4) has been designed and synthesized by utilising the intramolecular Eglinton cyclisation of an acyclic bis(triazolylalkyne)ferrocene precursor followed by alkylation. The anion sensing ability was investigated by
- aqueous/organic solvent mixtures [51]. A tetra-1,2,3-triazolium macrocycle 9 (Figure 9) was reported in 2012 by the Beer group. The synthesis was realized by using a CuAAC cyclisation of triazole bisazides and bisalkynes and subsequent alkylation. The charge-assisted C–H···anion interaction is used by
Genome mining in Trichoderma viride J1-030: discovery and identification of novel sesquiterpene synthase and its products
Beilstein J. Org. Chem. 2019, 15, 2052–2058, doi:10.3762/bjoc.15.202
- invertebrates [1][2]. More than 80,000 terpenoids have been identified and characterised [3][4][5]. These diverse and complex natural products are mostly derived from carbocation cyclisation with linear C5 isoprene precursors, which are catalysed by terpene synthases (TPSs) [6]. TPSs can be classified into
- three types based on their amino acid sequence. Type I TPSs are metal-dependent enzymes that initiate cyclisation by the elimination of diphosphate groups from precursors and carbocation formation, and type II TPSs initiate the catalytic process by the protonation of an olefinic double bond [7]. The
- universal linear precursor farnesyl pyrophosphate (FPP) and assembled by FPP synthases, using dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) as substrates. The subsequent elimination of diphosphate from FPP is catalysed by sesquiterpene synthases, with further cyclisation steps to form
Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition
Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200
- moieties, and careful basification resulted in intramolecular cyclisation givnig 5b,c with a yield of 51% and 42%, respectively. Nitrones 5a–c readily react with 4-pentenylmagnesium bromide. Quenching of the reaction mixtures with water under aerobic conditions leads to partial oxidation of resultant N
Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS)
Beilstein J. Org. Chem. 2019, 15, 1945–1961, doi:10.3762/bjoc.15.190
- deuterated compounds, multistage cyclisation reactions in the course of sesquiterpene biosynthesis could be substantiated for the first time for several structural classes in V. vinifera. Results and Discussion The HS-SPME–GC×GC–TOF–MS analysis of the grape variety Lemberger (Vitis vinifera subsp. vinifera
- NPP are possible as intermediates of terpene biosynthesis, since the absolute configurations of their products from Vitis vinifera L. are unknown and the subsequent cyclisation reactions can be explained by the enantiomers of germacrene D [30][31]. In order to investigate whether the formation of δ
Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate
Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134
- our compound 5. The formation of compound 8 can be explained by the rearrangement of 7 through a hydrogen-shift to form the diazo intermediate 9 which underwent a concerted [2 + 3] intramolecular cyclisation to 3,3-diphenyl-3H-indazole 8 (Scheme 2). The process was facilitated by the presence of a
- method a or b, respectively. The results confirm our initial hypothesis that the cyclisation occurred through the diazo species 9 (Scheme 2) and the Cu2+ plays no part in the reaction process. Conclusion The formation of the unexpected product 8 from 5 under anhydrous diazotisation conditions has led to
Phylogenomic analyses and distribution of terpene synthases among Streptomyces
Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115
- gray and dark gray circles). The 2-MIB synthases are present in members of all the three clades from the whole genome phylogenetic tree (Figure 1), but are most abundant in members of the clade depicted in red. These terpene synthases catalyse a unique cyclisation reaction utilizing the modified
- substrate 2-methyl-GPP to form 2-MIB (2) [25][26]. An S-adenosylmethionine (SAM) dependent methyl transferase is responsible for the methylation of GPP into 2-methyl-GPP (14, Scheme 2). Its isomerisation to 15 allows for a cyclisation via the cationic intermediates B and C to 2. Genes encoding for SAM
- enantiomers of the corresponding alcohols (R)- and (S)-albaflavenol (16ab) and the epoxide 4β,5β-epoxy-2-epi-zizaan-6β-ol (18) are known oxidation products that are all made by a cytochrome P450 monooxygenase [10][29] that is genetically clustered with the epi-isozizaene synthase for the cyclisation of FPP to
Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum
Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99
- diphosphate. In-depth mechanistic investigations using isotopically labelled precursors regarding the stereochemical course of both 1,11-cyclisation and 1,3-hydride shift furnished a detailed catalytic model suggesting the molecular basis of the observed low product selectivity. The enzyme’s synthetic
- TSs is largely unknown [12]. In this study, we present the characterisation of a bacterial TS with a reduced selectivity both for substrates and for products together with the challenging investigation of its cyclisation mechanism by labelling experiments. Results and Discussion A bacterial β
- and 15 in the incubation with GPP and 18 in the experiment with GGPP, this TS from C. arvum is characterised as a multiproduct (+)-β-himachalene synthase (HcS) possessing additional mono- and diterpene cyclase activity. The structures of its minor products reveal the cyclisation mechanism of HcS Since
An improved synthesis of adefovir and related analogues
Beilstein J. Org. Chem. 2019, 15, 801–810, doi:10.3762/bjoc.15.77
- were unable to access 2 (Scheme 7). Instead, the major product isolated in both cases was novel heterocycle 35. It is likely that cleavage of one of the pivaloxymethyl groups, followed by intramolecular cyclisation, results in the formation of 35. Microwave heating of 33 in the presence of DBU also
Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum
Beilstein J. Org. Chem. 2019, 15, 789–794, doi:10.3762/bjoc.15.75
- Jan Rinkel Jeroen S. Dickschat Kekulé-Institute for Organic Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany 10.3762/bjoc.15.75 Abstract A newly identified bacterial (Z)-γ-bisabolene synthase was used for investigating the cyclisation mechanism of the
- recombinant enzyme, which resolved in an exclusive cyclisation of (R)-NPP, while (S)-NPP that is non-natural to the (Z)-γ-bisabolene synthase was specifically converted into (E)-β-farnesene. A hypothetical enzyme mechanistic model that explains these observations is presented. Keywords: biosynthesis
- stereochemical imprint of a TS on achiral products is not directly visible, there still can be a chiral cyclisation cascade behind these terpenes. This is true as well for examples featuring a mirror plane like the monoterpene 1,8-cineol (eucalyptol, 3), for which the absolute configuration of the intermediary
Efficient synthesis of 4-substituted-ortho-phthalaldehyde analogues: toward the emergence of new building blocks
Beilstein J. Org. Chem. 2019, 15, 721–726, doi:10.3762/bjoc.15.67
- cyclisation in a basic medium of 2 then occurred to generate 4,5-dihydroisobenzofuran-5-ol (3) [19]. At this step, Cao et al. [17] have chosen the direct oxidation of 4,5-dihydroisobenzofuran-5-ol (3) to obtain 4-HO-OPA by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an oxidant. However, the yield
Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands
Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19
- alia the cyclisation of hex-5-enyl undec-10-enoate to oxacyclohexadec-11-en-2-one (50% at 60 °C in toluene) and the ROMP of dicyclopentadiene. They were also able to immobilise these Grubbs 1-type precatalysts using dendritic pyridinyl alcohols [8]. These complexes catalysed the RCM reaction (at 80 °C
Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum
Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277
- acetate, two non-reducing elongations with malonyl-SCoA, the first without and the second with C-methylation, followed by another elongation with reduction of the 3-oxo group and cyclisation yields the aromatic system of 25 and 26. Hydrolytic cleavage from the ACP and two methylations of the phenol and
Unprecedented nucleophile-promoted 1,7-S or Se shift reactions under Pummerer reaction conditions of 4-alkenyl-3-sulfinylmethylpyrroles
Beilstein J. Org. Chem. 2018, 14, 2722–2729, doi:10.3762/bjoc.14.250
- -carboxamides that produces pyrrolo[2,3-c]- and [2,3-d]azepinones [30][31]. However, this reaction is not suitable for the synthesis of pyrrolo[3,2-c]azepines in viewpoint of the difficulties in preparing the starting materials. We previously reported that the hydroamination/cyclisation reaction of sulfanyl-1,6
- cyclisation reactions. Results and Discussion We prepared sulfoxides as substrates for the Pummerer reactions according to the aforementioned method [32][33]; subsequently, oxidation with mCPBA was performed (Scheme 2). Both the allylic sulfides 4a–f and their sulfoxides 5a–f were obtained in good to high
- yields. Corresponding pyrroloselenides 6a–f were prepared by applying a similar synthetic sequence; however, the selenoxides could not be obtained by implementing the usual reaction conditions. The structure of the products derived from the amination–cyclisation reaction of sulfanyl 1,6-diyne 1a was
Synthesis and biological evaluation of 1,2-disubstituted 4-quinolone analogues of Pseudonocardia sp. natural products
Beilstein J. Org. Chem. 2018, 14, 2680–2688, doi:10.3762/bjoc.14.245
- primary amines 12, which following metal-catalysed cyclisation would give 1,2-disubstituted quinolones 14. Upon the successful synthesis of analogues of the form 14, biological evaluation of these and the natural products 1, 4 and 5–7 (synthesised during our previous study [11]) would then be possible. In
- flash column chromatography, which may account for the slightly lower yields in these cases (13ad and 13ae). With the compounds 13 now in hand, their cyclisation to the desired analogues 14 was explored. However, whilst the conditions which had proved successful in the total synthesis of natural
- to moderate (Scheme 4), sufficient quantities were obtained to facilitate biological screening. It appeared that bulkier N-substituents (e.g., 14ae) resulted in lower yields than less bulky derivatives (e.g., 14bf), underlining the importance of steric factors during cyclisation. Interestingly, the
Synthesis of functionalised β-keto amides by aminoacylation/domino fragmentation of β-enamino amides
Beilstein J. Org. Chem. 2018, 14, 2602–2606, doi:10.3762/bjoc.14.238
- only upon heating in TFA solution, but then the cyclisation mode is completely different and leads to enaminotetramic derivatives 10 instead of pyrrolin-4-ones 6 [34]. Another drawback caused by the acidic deprotection conditions was the loss of chiral integrity. When the deprotection of 3 was
- for compounds 5 (87:13–80:20) were obtained with TFA/CH2Cl2 (1:4) and 15 min deprotection time, without any change in the yields indicated in Table 1. Experiments with more dilute TFA required longer deprotection time, which in turn gave advantage to the unwanted cyclisation to pyrrolinones 6 and
- -ketoamides 11 The longer chain in compounds 4 precludes the favourable 5-exo-trig process discussed earlier (Scheme 3) and accordingly there was no competing formation of cyclic side products. A different type of unwanted cyclisation occurred with the GABA derivatives 4b,c,f,j (n = 2) but here the competing
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