Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• including cinchona alkaloid derivatives, chiral phosphoric acids, chiral amino alcohols, chiral thioureas, chiral guanidines, and chiral 1,2,3-triazolium chlorides. In this review, the research work of enantioselective desymmetrization of meso-aziridines is organized into sections according to the employed

• yields. Interestingly, meso-N-tosylaziridines reacted sluggishly in both chloroform and toluene as the solvents under the same catalytic system, and the reason of this phenomenon is unknown. Chiral thioureas Jacobsen [50] and co-workers presented an enantioselective catalytic desymmetrization of meso-N

• -benzoylaziridines with HCl by a series of chiral thioureas (Figure 8, OC-28 to OC-44). In most of the cases, a diluted reaction mixture is necessary to obtain good enantioselectivities and OC-41 proved to be the best catalyst to provide β-chlorobenzamides (Scheme 8, 60 to 66) in high yields and enantioselectivities

Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

• Carsten S. Kramer and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 1414–1418, doi:10.3762/bjoc.9.158

• carbenes, guanidines, thioureas, amidinium ions, diols, and Brønsted acids showed their value to give densely functionalized Diels–Alder products in high selectivities [1][2][3][4][5][6][7]. In addition, some organocatalysts enabled even the formation of quaternary centers in Diels–Alder cycloadditions [3

• of one equivalent of Brønsted acid 8 had no effect (Table 2, entry 4), the addition of TADDOL (9) improved the reaction speed (Table 2, entry 5). By the use of Schreiner's catalyst 10 [7], the highest conversion speed was observed (Table 2, entry 6). After this finding, Jacobsen's thioureas 11 [13

• ] (Table 2, entry 7) and 12 [14] (Table 2, entry 8) were also tested whereby the 3,5-bis(trifluoromethyl)phenyl-substituted thiourea 12 was superior to catalyst 11. The fact that thioureas as well as diol 9 improved the reaction speed was coherent, since both catalysts are well known to catalyze the Diels

A facile, rapid, one-pot regio/stereoselective synthesis of 2-iminothiazolidin-4-ones under solvent/scavenger-free conditions

• Murugan Sathishkumar,
• Sangaraiah Nagarajan,
• Poovan Shanmugavelan,
• Murugan Dinesh and
• Alagusundaram Ponnuswamy

Beilstein J. Org. Chem. 2013, 9, 689–697, doi:10.3762/bjoc.9.78

• hypnotic [7][8], antitubercular [9], cardiovascular [10] and cyclooxygenase (COX) inhibitory [11] activities (Figure 1). A common strategy involved in the prevailing synthetic protocols for 2-iminothiazolidin-4-ones [12][13][14] is the cyclization of thioureas with α-halocarboxylic acids [15] or acyl

Efficient synthesis of β’-amino-α,β-unsaturated ketones

• Isabelle Abrunhosa-Thomas,
• Aurélie Plas,
• Nishanth Kandepedu,
• Pierre Chalard and
• Yves Troin

Beilstein J. Org. Chem. 2013, 9, 486–495, doi:10.3762/bjoc.9.52

• under different protocols in which the stereoselectivity of the reaction can be introduced through the use of a chiral catalyst [9][10] (Lewis acid, Brønsted acids, L-proline, Cinchona alkaloids derivatives, thioureas, etc.), or by the addition of chiral amines to α,β-unsaturated esters [11][12] or the

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• thiochromenes; and (3) Organocatalytic aza-Michael reactions to access functionalized 1,2-dihydroquinolines, using chiral proline and its derivatives (Figure 2), chiral bifunctional thioureas, cinchona alkaloids and other organocatalysts (Figure 3). For each reaction, the initial screening result of various

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity

• Tatyana E. Shubina,
• Matthias Freund,
• Sebastian Schenker,
• Timothy Clark and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2012, 8, 1485–1498, doi:10.3762/bjoc.8.168

• guanidine-thiourea organocatalysts would perform as well as or even better than amine-thioureas and imidazole-thioureas. Generally, guanidines are well-known basic catalysts in organic synthesis, but only scattered examples of chiral guanidines as organocatalysts are known [49]. Indeed, only one guanidine

Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis

• Marcus Frings,
• Isabelle Thomé and
• Carsten Bolm

Beilstein J. Org. Chem. 2012, 8, 1443–1451, doi:10.3762/bjoc.8.164

• catalysts in high overall yields without affecting the stereohomogeneity of the sulfur-containing core fragment. Keywords: anhydride opening; catalytic asymmetric Biginelli reaction; organocatalysis; sulfoximines; thioureas; Introduction Since their discovery in the middle of the last century

• reactions in a highly enantioselective manner has no end in sight. In this context, thiourea-based organocatalysts have caught significant attention due to their ability to activate substrates through hydrogen-bonding [42][43][44][45][46][47]. Usually, these chiral thioureas are classified into several

• categories, for example, being mono- or bis-thioureas. Furthermore, they can be mono- or bifunctional with variably weak amine (primary, secondary, tertiary) or amide groups attached. Figure 2 illustrates a few selected examples of the aforementioned chiral thioureas which have successfully been applied in

Highly enantioselective access to cannabinoid-type tricyles by organocatalytic Diels–Alder reactions

• Stefan Bräse,
• Nicole Volz,
• Franziska Gläser and
• Martin Nieger

Beilstein J. Org. Chem. 2012, 8, 1385–1392, doi:10.3762/bjoc.8.160

• ) [33]. The yields were good to excellent in all procedures (Table 1). These thioureas were used in an intermolecular Diels–Alder reaction of diene 10 [36] with acrolein (11) to obtain cannabinoid tricycle 5 shown in Scheme 2. In all cases we only achieved one cis-diastereomer and the carbonyl function

• from 68% to 99% depending on the substitution of the thiourea-catalyst 9a–l (Table 2). When the substitution of the various thioureas 9a–l is further compared with the obtained yields in the Diels–Alder reaction (Table 2), the following tendencies are also observed. A noticeable fact is that, in

• contrast to the thioureas with a cyclopropyl- and m-halophenyl-moiety (Table 2, entries 7–9), the corresponding bis(trifluoromethyl)thioureas (Table 2, entries 16–18) provide a higher conversion. Next to the previously described thiourea catalysts, we also analyzed iminium-ion catalysts according to

Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts

• Saet Byeol Woo and
• Dae Young Kim

Beilstein J. Org. Chem. 2012, 8, 699–704, doi:10.3762/bjoc.8.78

• , bifunctional tertiary-amine thioureas, thiophosphorodiamides, and squaramide-based organocatalysts [34][35][36]. Findings In the framework of our research program for the development of synthetic methods for the enantioselective construction of stereogenic carbon centers [37][38][39][40][41][42], we recently

A general and facile one-pot process of isothiocyanates from amines under aqueous conditions

• Nan Sun,
• Bin Li,
• Jianping Shao,
• Weimin Mo,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2012, 8, 61–70, doi:10.3762/bjoc.8.6

• for potential medical applications [3][4][5][6]. Morevoer, isothiocyanates are pivotal intermediates in organic synthesis, especially in the synthesis of various heterocyclic compounds [7][8] and unsymmetric thioureas [9][10][11][12]. Although many synthetic methods for the preparation of

• isothiocyanates – is still a challenge in organic chemistry. Results and Discussion Previously, Furumoto reported the application of cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) as a desulfurylation reagent in the synthesis of carbodiimides from thioureas under mild conditions [60]. In that reaction

• , the S-nucleophiles first reacted with TCT and then decomposed to release the product carbodiimides and by-product 2,4,6-trimercapto-1,3,5-triazine (TMT) [61]. Considering that TCT is an efficient desulfurylation reagent of thioureas to synthesize carbodiimides and that it is affordable in large scale

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• SO17 1BJ, United Kingdom Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia 10.3762/bjoc.7.140 Abstract The conformational properties of 1,3-diindolylureas and thioureas were studied by a combination of heteronuclear NMR spectroscopy and quantum

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

• Kumaresh Ghosh and
• Debasis Kar

Beilstein J. Org. Chem. 2011, 7, 254–264, doi:10.3762/bjoc.7.34

• hydrogen bond donors and acceptors are of considerable importance. Among the different binding motifs for anions, the hydrogen bonding properties of NH groups in neutral amines [13], amides [14], ureas/thioureas [15][16], indoles [17][18][19] and pyrroles [20] as well as in guanidinium [21] and imidazolium

A new and facile synthetic approach to substituted 2-thioxoquinazolin-4-ones by the annulation of a pyrimidine derivative

• Nimalini D. Moirangthem and
• Warjeet S. Laitonjam

Beilstein J. Org. Chem. 2010, 6, 1056–1060, doi:10.3762/bjoc.6.120

• -thioxoquinazolin-4-ones, as most of the methods reported are for quinazolin-2,4(1H,3H)-diones. Recently, Saeed et al. [18] reported the base catalyzed intramolecular nucleophilic cyclization of substituted thioureas in the presence of DMF to afford 2-thioxoquinazolin-4-ones. The preparation of 2-thioxoquinazolin-4

• active methylene compounds, such as, malononitrile and ethylcyanoacetate. Results and Discussion DTBA are among the simplest synthetic intermediates and can be easily prepared in a one-pot reaction by treating 1,3-diaryl thioureas with malonic acid in the presence of acetyl chloride. DTBA undergoes

Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea

• assemblies as a hydrogen bond donor. For this purpose, we synthesized the bis-thiourea S4, from the corresponding bis-thioisocyanate, because thioureas are known to be strong hydrogen bond donors and weak hydrogen bond acceptors [34][35]. Before evaluating the chain stopper efficiency of these compounds, i.e

• ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. Depending on the solvent used, the bis-urea either forms filaments with a single monomer in the cross-section or tubes with three monomers in the cross-section. For both supramolecular architectures

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• , thioureas can be easily transformed into carbodiimides and thus serve as key intermediate in the synthesis of other pseudoamide functionalities (urea, guanidine, etc.) [70][71][72][76][77][78][79]. Thirdly, thiourea bridges provide efficient anchoring points for bidentate hydrogen-bonding recognition, which

• monosaccharide units in glycooligomers is particularly attractive with regard to molecular recognition processes. Like thioureas and ureas, guanidines can also form bidentate hydrogen bonds. In addition, because of their positively charged character, guanidines can exert strong electrostatic interactions with

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• prepared from the (acylamino)cyanoacetates 5b,c, which in turn were derived from ethyl cyanoglyoxylate oxime (4) by reduction followed by acylation by isobutyric anhydride or azidoacetyl chloride (Figure 3). Reaction of the aminooxazoles 3b,c with benzoylisothiocyanate afforded the thioureas 6b,c. Direct

• cyclization of 6b,c to oxazolo[5,4-d]pyrimidines 2b,c by treatment with ammonia in methanol was unsuccessful. However, thioureas 6b,c were converted to the desired 2-substituted the oxazolo[5,4-d]pyrimidines 2b,c by stepwise methylation followed by cyclization in the presence of ammonia in methanol. Although

The first organocatalytic carbonyl- ene reaction: isomerisation- free C-C bond formations catalysed by H-bonding thio- ureas

• Matthew L. Clarke,
• Charlotte E. S. Jones and
• Marcia B. France

Beilstein J. Org. Chem. 2007, 3, No. 24, doi:10.1186/1860-5397-3-24

• interest in hydrogen bond mediated catalysis,[11] we have investigated thioureas as H-bonding additives for organocatalytic carbonyl ene reactions and report these results here. Despite the explosive growth in organocatalytic reactions in recent years, [12][13][14][15][16] this represents, to the best of