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Search for "thiourea" in Full Text gives 190 result(s) in Beilstein Journal of Organic Chemistry.
Efficient mechanochemical synthesis of regioselective persubstituted cyclodextrins
Beilstein J. Org. Chem. 2016, 12, 2364–2371, doi:10.3762/bjoc.12.230
- impurities, could be performed. Isolation and purification processes could also be simplified. Considerably lower alkylthiol/halide ratio were necessary to reach the complete reaction in comparison with thiourea or azide reactions. While the presented mechanochemical syntheses were carried out on the
- well as solvent impurities increase synthesis and purification costs and time. Selectively per-6-thiolated CDs are also used in gold nanoparticle chemistry, particularly in electrochemical sensors [17]. Thiourea (TU) is one of the best precursors of those CDs because as the halogen is exchanged to the
Highly chemo-, enantio-, and diastereoselective [4 + 2] cycloaddition of 5H-thiazol-4-ones with N-itaconimides
Beilstein J. Org. Chem. 2016, 12, 2293–2297, doi:10.3762/bjoc.12.222
- . Results and Discussion Our studies were initiated by examining a model reaction between 5H-thiazol-4-one 1a and N-phenyl itaconimide 2a (Table 1). The reaction was first evaluated in toluene at 25 °C and using L-tert-leucine-based thiourea−tertiary amine I as the catalyst (Table 1, entry 1), with
- chemoselectivity and thus the moderate yield. When the H-bond donor was changed from thiourea to urea (catalyst II), it did not provide better results (Table 1, entry 2) [17][19]. In the [4 + 2] annulation of 5H-thiazol-4-ones with nitroalkenes, dipeptide-based thiourea−amide−tertiary amine III (DP-TAA) was
- dipeptide-based tertiary amine for this type of reaction. By modifying the thiourea moiety of III to urea lead us to catalyst DP-UAA IV, which could further increase the enantioselectivity (Table 1, entry 4). Subsequently, we screened the solvent effect with IV as the catalyst (Table 1, entries 5–7), and
Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes
Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190
- ]. Some urea and thiourea derivatives have been studied as CNS agents [7] and anthelmintic drugs [8]. This heterocyclic core therefore represents the foundation for potential bioactive agents. A few methods have been described for the synthesis of 2-iminoazacycloalkanes from acyclic precursors. One
A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis
Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176
- reductive amination to form 18 (58%). After removal of the Boc protecting group (quant.), triamine 19 was reacted with dimethyl trithiocarbonate in refluxing nitromethane. The thiourea intermediate was activated in situ by S-alkylation with MeI. Upon further heating the final cyclization occured forming the
Rearrangements of organic peroxides and related processes
Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162
- additional reaction step [345] (Scheme 69). The treatment of endoperoxide 232 with triethylamine in ethanol at room temperature results in the O–O-bond cleavage to form 5-hydroxytropolone (233) (Scheme 70) [346]. It is interesting to note, that a reduction of the bicyclic endoperoxide 234 with thiourea in
Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates
Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121
- (Scheme 19). 2.2.5 Pyrimidinylphosphonates: The 1,3-bi-nucleuphiles such as thiourea (82), guanidinium carbonate 84 and cyanoguanidine 86, under the above mentioned conditions afforded the pyrimidinylphosphonates 83, 85 and 87, respectively (Scheme 20). 2.2.6 Diazepinyl- and oxazepinylphosphonates: The
- this method, the one-pot reaction of isatin derivatives 301, iminophosphorane 302, and diphenyl phosphonate in the presence of Cinchona-derived thiourea as the catalyst afforded α-aminophosphonates 303 in 70–81% yields and with 70–84% ee (Scheme 62) [100]. The trans-1,5-benzodiazepines 307 bearing both
- . Three-component reaction of 6-methyl-3-formylchromone (75) with thiourea, guanidinium carbonate or cyanoguanidine in the presence of diethyl phosphonate. Three-component reaction of 6-methyl-3-formylchromone (75) with 1,4-bi-nucleophiles in the presence of diethyl phosphonate. One-pot three-component
Conjugate addition–enantioselective protonation reactions
Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116
- thiourea catalyst 92 in high yield and modest enantioselectivity (Scheme 22) [45]. Tan and co-workers have investigated the conjugate addition–enantioselective protonation of N-arylitaconimides 95 using a C2-symmetric guanidine catalyst (Scheme 23) [24][46]. Because E- and Z-enolates can exhibit different
- (Scheme 23c). Following Tan’s work on the conjugate addition–enantioselective protonation of cyclic itaconimide 95, both the Singh and Chen groups investigated the addition of thiol nucleophiles to acyclic imides. Utilizing thiourea catalyst 102a, Singh and co-workers reported the catalytic
- ). Building on their addition of benzylic and aromatic thiols to N-acryloyloxazolidinones, Singh and colleagues demonstrated that thiourea 102b catalyzes the addition of thioacetic acid to N-acryloyloxazolidinones in high yields and enantioselectivity to provide thioester 101b [48]. In a related
Towards the total synthesis of keramaphidin B
Beilstein J. Org. Chem. 2016, 12, 1096–1100, doi:10.3762/bjoc.12.104
- pronucleophile to a substituted furanyl nitroolefin catalysed by a bifunctional cinchonine-derived thiourea has been used as the key stereocontrolling step in a new synthetic strategy to the heavily functionalised piperidine core of keramaphidin B. Keywords: bifunctional organocatalyst; enantioselective Michael
- reported cinchonine-derived bifunctional thiourea catalyst 12 afforded the addition product 13 in high yield with good levels of diastereo- and enantioselectivity (95:5 dr, 90:10 er for the major diastereomer 13). The relative stereochemical configuration of the minor diastereomeric product 14 was
- hydroxypropyl chain attached to the quaternary stereocentre, poised for further functionalisation. Having established that the cinchonine-derived bifunctional Brønsted base/thiourea organocatalyst 12 was effective for installing two stereocentres including the quaternary carbon in a model system, we next
Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update
Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98
- , heterocyclic groups and aliphatic groups. A plausible mechanism was proposed as shown in Scheme 29. The thiourea NH moieties and the tertiary amino group of the catalyst activated the carbonyl groups of isatin and the α-protons of gem-diols, respectively through hydrogen bond interactions. The α-proton of gem
- same group reported the organocatalytic asymmetric addition reactions of isatins with electron-rich aromatics sesamols using the cinchona alkaloid-derived thiourea catalyst (cat. 17) under mild conditions. In the presence of 10% catalyst, sesamols reacted with isatins smoothly in tert-butyl ether at
- of the bifunctional thiourea catalyst (cat. 24, 10 mol %), affording the E-adducts in high yields (up to 95%) and with moderate to good enantioselectivities (up to 99% ee). Different allyl ketones were examined under these conditions, affording the corresponding products in good yields, especially
1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis
Beilstein J. Org. Chem. 2016, 12, 918–936, doi:10.3762/bjoc.12.90
- -alkylation. The starting thiohydantoins, in turn, are obtained by heating a mixture of the corresponding N-substituted amino acid or its methyl ester 3 and thiourea at 195 °C [59] (Scheme 1b). Following this protocol different 1H-Imidazol-4(5H)-ones have been prepared in good yields. 1.2 1H-Imidazol-4(5H
- acceptors in reactions promoted by bifunctional Brønsted bases. 1.2.1 Nitroalkenes as acceptors. Investigation of the base-catalyzed Michael addition reaction of 2-thio-1H-imidazol-4(5H)-ones 4 to nitroalkenes 5 [55] revealed that cinchona alkaloids such as quinine, (DHQ)2Pyr or even thiourea tertiary amine
- (Scheme 8) [85]. This catalyst belongs to a new subclass of bifunctional Brønsted bases, which was developed on the basis of Takemoto’s model [86]. This model is featured by three different moieties: a basic site, a urea (thiourea) function and a 3,5-bis(trifluoromethyl)phenyl group, all three elements
Asymmetric α-amination of 3-substituted oxindoles using chiral bifunctional phosphine catalysts
Beilstein J. Org. Chem. 2016, 12, 725–731, doi:10.3762/bjoc.12.72
- (diethyl azodicarboxylate, 2a) was selected as the model reaction for the evaluation of chiral phosphine catalysts (Table 1). Using bifunctional thiourea catalysts 4a and 4b, the reaction proceeded smoothly at room temperature to afford the product 3a in good yields, albeit with low enantiomeric excesses
- (ee) (Table 1, entries 1 and 2). When the thiourea moiety in the catalysts were replaced by amides, the enantioselectivities were greatly improved (Table 1, entries 3–6). The examination of catalysts 4c–f with further fine-tuning on the acyl group revealed 4d as the optimal catalyst for this
Stereoselective amine-thiourea-catalysed sulfa-Michael/nitroaldol cascade approach to 3,4,5-substituted tetrahydrothiophenes bearing a quaternary stereocenter
Beilstein J. Org. Chem. 2016, 12, 643–647, doi:10.3762/bjoc.12.63
- nitroalkenes and commercially available 1,4-dithiane-2,5-diol to 3,4,5-substituted tetrahydrothiophenes, bearing a quaternary stereocenter, is presented. A secondary amine thiourea derived from (R,R)-1,2-diphenylethylamine was found to be the most effective catalyst when using trans-β-methyl-β-nitrostyrenes
- - and enantioselectivity (Table 1, entries 1–5). Thiourea catalyst VII afforded the best result, leading to products 5/6 in a ratio of 72/28 although with low ee values (Table 1, entry 6). Reacting trisubstituted olefin 2a with compound 4, led to three isomers with modest diastereocontrol when using
- catalysts (I–VII). Among the catalysts tested, compound VII proved to be the most active and enantioselective, giving the major diastereoisomer 7a with 44% ee (Table 1, entry 13). Taking into account that amine thiourea VII, bearing a sterically hindered secondary amine moiety, was significantly more
Supported bifunctional thioureas as recoverable and reusable catalysts for enantioselective nitro-Michael reactions
Beilstein J. Org. Chem. 2016, 12, 628–635, doi:10.3762/bjoc.12.61
- bifunctional thioureas on sulfonylpolystyrene resins has been studied in the nitro-Michael addition of different nucleophiles to trans-β-nitrostyrene derivatives. The activity of the catalysts depends on the length of the tether linking the chiral thiourea to the polymer. The best results were obtained with
- the thiourea derived from (L)-valine and 1,6-hexanediamine. The catalysts can be used in only 2 mol % loading, and reused for at least four cycles in neat conditions. The ball milling promoted additions also worked very well. Keywords: bifunctional organocatalysts; organocatalysis; stereoselective
- thiourea I [30] onto sulfonylpolystyrene resin leading to catalysts II–V (Figure 1), which differ in the length of the diamine linker or in the substitution pattern of the nitrogen in the sulfonamide. These materials, and the related unsupported thiourea VI, have been previously tested as excellent
The aminoindanol core as a key scaffold in bifunctional organocatalysts
Beilstein J. Org. Chem. 2016, 12, 505–523, doi:10.3762/bjoc.12.50
- formation of catalytically active oxazaborolidines using cis-1,2-aminoindanol derivatives [9][10] and (b) the synthesis of more active cooperative thiourea-urea-based organocatalysts, which employ the aminoindanol framework as structural linker between two hydrogen-bond-donor moieties [11]. The latter ones
- acting through hydrogen bonding, such as thiourea, urea, squaramide, and thioamide frameworks. These have been efficiently employed in a few organocatalytic processes such as Friedel–Crafts alkylations, Michael additions, Diels–Alder reactions and aza-Henry reactions, as discussed below. Friedel–Crafts
- -type alkylation reaction of indoles To the best of our knowledge, the first example of an aminoindanol-containing bifunctional organocatalyst was reported by Ricci and co-workers in 2005 [18]. In this pioneering study, the authors used the easily prepared cis-(1R,2S)-aminoindanol-based thiourea
(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers
Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48
- chiral centers; organocatalysis; six-membered ring; thiourea; urea; Introduction During the last 15 years, organocatalysis has flourished and has been established as one of the three major pillars of asymmetric synthesis [1][2][3]. Among the modes of activation of organic molecules that have been
- also achieved organocatalytically with hydrogen bonding. Organocatalysts that contribute to hydrogen bond formation bear usually a urea or thiourea moiety and they mostly interact with carbonyl groups, nitro moieties or even imines that exist to the substrates, leading to increased electrophilicity
- ; urea and thiourea moieties have also been proposed to interact with nucleophiles. Besides the fact that hydrogen bond donors increase the electrophilicity of the substrates, they mostly coordinate the transition state of the reaction, controlling this way the stereoselectivity of the products. It has
Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts
Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46
- asymmetric organocatalysis. This fascinating class of bifunctional catalyst offers a genuine alternative to the more commonly used thiourea systems and because of the different spacing between the functional groups, can control enantioselectivity where other organocatalysts have failed. In the main, this
- optimize their stereoselective behaviour has seen their utility burgeon dramatically over the last decade. Of particular note is the use of these cinchona systems within bifunctional thiourea catalysis [3][4][5][6][7][8][9][10][11][12]. Cupreine (CPN) and cupreidine (CPD), the non-natural demethylated
Organocatalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones with bifunctional amine-thiourea catalysts bearing multiple hydrogen-bond donors
Beilstein J. Org. Chem. 2016, 12, 295–300, doi:10.3762/bjoc.12.31
- 100049, China 10.3762/bjoc.12.31 Abstract For the first time, a catalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones was achieved with a chiral bifunctional amine-thiourea as a catalyst possessing multiple hydrogen-bond donors. With this developed method, a range of 3-hydroxy-3-nitromethyl-1H
- bifunctional multiple hydrogen-bond amine-thiourea-catalyzed Michael reaction of acetyl phosphonates with nitroolefins, giving a series of β-substituted nitro compounds with excellent stereoselectivity [34]. Therefore, as part of our research program aimed at establishing new methods for the construction of
- quaternary stereocenters [35][36][37], we envisioned that the Henry reaction of nitroalkanes with 1H-pyrrole-2,3-diones should take place with a chiral bifunctional amine-thiourea catalyst, leading to 3-hydroxy-3-nitromethyl-1H-pyrrol-2(3H)-ones bearing quaternary stereocenters (Scheme 1) [14]. Notably, this
Enabling technologies and green processes in cyclodextrin chemistry
Beilstein J. Org. Chem. 2016, 12, 278–294, doi:10.3762/bjoc.12.30
- ester in C-6 with thiourea followed by basic hydrolysis. The reaction gave the thiouronium salt after 1 h of irradiation at 100 °C while 20 h heating at 90 °C are required under conventional conditions [21]. While the previous experiments were performed in a multimode MW oven (MicroSynth-Milestone
A quadruple cascade protocol for the one-pot synthesis of fully-substituted hexahydroisoindolinones from simple substrates
Beilstein J. Org. Chem. 2016, 12, 253–259, doi:10.3762/bjoc.12.27
- reactions, we also tested thiourea catalysts, cat-1 to cat-3. Interestingly, the thioureas cat-1 and cat-2 were able to promote the reaction (Table 1, entries 7 and 8), but we obtained an even better yield when the tertiary amine-thiourea cat-3 was used as the catalyst (Table 1, entry 9). All products were
Catalytic asymmetric formal synthesis of beraprost
Beilstein J. Org. Chem. 2015, 11, 2654–2660, doi:10.3762/bjoc.11.285
- . Amide 8 was similarly synthesized in 48% yield from 10. With the Michael precursors in hand, we next investigated the key AIOM reaction of 7 and 8 (Table 1). When the methylated substrate 7 was employed, the thiourea B [34][35] or benzothiadiazine C [33][36][37][38] catalysts efficiently promoted the
- reaction to furnish the dihydrobenzofuran 6 in 90% yield with high enantioselectivities (Table 1, entries 2 and 3). Conversely, thiourea A showed less catalytic activity, and the reaction required a much longer time for completion (Table 1, entry 1), indicating that the HB-donor moiety played an important
Bifunctional phase-transfer catalysis in the asymmetric synthesis of biologically active isoindolinones
Beilstein J. Org. Chem. 2015, 11, 2591–2599, doi:10.3762/bjoc.11.279
- elaborations en route to the targets of medicinal interest (Figure 1). A high yield (usually >95%) and a maximum level of enantioselectivity of 74% ee were obtained but only in the presence of large amounts of cinchona alkaloid-based thiourea-containing organocatalysts (15 mol %) and after an unacceptably long
Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds
Beilstein J. Org. Chem. 2015, 11, 1486–1493, doi:10.3762/bjoc.11.161
- tandem process (Table 1, entries 9 and 10). The use of Lewis acids as co-catalysts was also tested although the efficiency of the process did not improve neither with Ti(OiPr)4 nor with BF3·OEt2 (Table 1, entries 11 and 12). Alternatively, thiourea derivatives have proven to be very effective hydrogen
One-pot odourless synthesis of thioesters via in situ generation of thiobenzoic acids using benzoic anhydrides and thiourea
Beilstein J. Org. Chem. 2015, 11, 1265–1273, doi:10.3762/bjoc.11.141
- the reaction of benzoic anhydrides, thiourea and various organic halides (primary, allylic, and benzylic) or structurally diverse, electron-deficient alkenes (ketones, esters, and nitriles) in the presence of Et3N has been developed. In this method, thiobenzoic acids were in situ generated from the
- reaction of thiourea with benzoic anhydrides, which were subjected to conjugate addition with electron-deficient alkenes or a nucleophilic displacement reaction with alkyl halides. Keywords: benzoic anhydride; Michael addition; nucleophilic displacement; thioester; thiourea; Introduction Thioesters have
- preparation of alkane thiols using thiourea and alkyl halides is a well-known reaction in organic synthesis. In addition, two methods for the synthesis of thioacids from acyl chlorides using N,N-dimethylthioformamide [51] or thioacetamide [52] have been reported. As far as we know, a similar reaction using
Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams
Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60
Sequence-specific RNA cleavage by PNA conjugates of the metal-free artificial ribonuclease tris(2-aminobenzimidazole)
Beilstein J. Org. Chem. 2015, 11, 493–498, doi:10.3762/bjoc.11.55
- approach towards tris(2-aminobenzimidazole), we adopted Lipton's method to the synthesis of aminobenzimidazoles. Thiourea 3 was prepared as described before [15], starting with the Boc-protection of tris(2-aminoethyl)amine (1) followed by the stepwise reaction of the free NH2 group of product 2 with
- thiocarbonyldiimidazole and methyl 3,4-diaminobenzoate (Scheme 2). The cyclisation to form the first benzimidazole unit was then achieved by reacting thiourea 3 with Mukaiyama’s reagent in the presence of NEt3 at rt yielding 88% of 4. Although the yield is slightly lower compared to the cyclisation with HgO (97% yield
- ), the mild and metal-free reaction conditions are a big advantage of this new method. For the subsequent two conversions, again the known procedures were used. Thiourea 6 was prepared by deprotection of 4 with SOCl2 in MeOH and addition of 2-nitrophenylisothiocyanate followed by reduction of the nitro
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