Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes

• Lucie Brulíková,
• Aidan Harrison,
• Marvin J. Miller and
• Jan Hlaváč

Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184

• -ethyl-2-oxazoline in methanol [69]. Additionally, acylnitroso compounds can be generated by the rearrangement of diazonitroalkanes 26 [70], the photochemical cleavage of 1,2,4-oxadiazole-4-oxides 25 [71] and the cycloreversion of 9,10-dimethylantracene adducts 27 (Scheme 7) [72][73]. Dienes: There is a

• ). Recent research of the Whiting group revealed a wide spectrum of results on the reactions of hydroxamic acid analogues 35 with various dienes 37 using the copper/oxazoline/air catalytic system (Scheme 10) [69]. Conclusions of an experimental as well as a computational approach to understanding the

• reactions of acylnitroso compounds in [4 + 2] cycloadditions indicate several facts. The copper–oxazoline complex behaves as an excellent catalyst for the aerobic oxidation of acylhydroxamic acids. However, this system is useful only for hydroxamic acids containing a heteroatom between the aryl and carbonyl

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• (Scheme 2) [15][16][17]. A Mg-(bis)oxazoline complex serves as both a Lewis acid for the activation of α-substituted acrylates 6 towards radical addition and as a chiral template for an enantioselective hydrogen atom transfer from Bu3SnH to the α-ester radical intermediate. The authors found that the

• stoichiometric chiral Mg-(bis)oxazoline complex was required to achieve high enantioselectivity. Higher enantioselectivity was generally observed for reactions using secondary or tertiary alkyl halides. When performing radical conjugate additons to give 2-hydroxymethyl esters 7c, the authors observed a complete

NeoPHOX – a structurally tunable ligand system for asymmetric catalysis

• Jaroslav Padevět,
• Marcus G. Schrems,
• Robin Scheil and
• Andreas Pfaltz

Beilstein J. Org. Chem. 2016, 12, 1185–1195, doi:10.3762/bjoc.12.114

• intermediate is a NeoPHOX derivative bearing a methoxycarbonyl group at the stereogenic center next to the oxazoline N atom. The addition of methylmagnesium chloride leads to a tertiary alcohol, which can be acylated or silylated to produce NeoPHOX ligands with different sterical demand. The new NeoPHOX

• efficiency and excellent enantioselectivity. Among the many oxazoline-derived ligands that have been reported in the literature, SimplePHOX [17] and ThrePHOX [18] have emerged as some of the most versatile and most easily accessible ligand classes. However, although iridium complexes derived from these

• state-of-the-art oxazoline-based ligands is the high cost of tert-leucinol as starting material, which reduces their potential for industrial-scale application. We therefore thought of ways to replace the tert-butyloxazoline ring by an equally effective oxazoline unit derived from a less expensive

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• allylated product in 93% yield and 72% ee value when cat. 2 was used (Scheme 2). Kesavan and co-workers described that the Pd/bis(oxazoline) (L1) complex can catalyze the asymmetric allylation of 3-O-Boc-oxindole, yielding the 3-allyl-3-hydroxyoxindoles in good yields (up to 93% yield) and with high

• the Cu(OTf)2 as the catalyst (10 mol %) and a fluorinated bis(oxazoline) L2 as the ligand (10 mol %), affording the products in moderate yields (up to 66% yield) and with good to excellent enantioselectivities (up to 92% ee). Interestingly, the fluorinated bis(oxazoline) L2 can be recovered and reused

Enantioselective carbenoid insertion into C(sp³)–H bonds

• J. V. Santiago and
• A. H. L. Machado

Beilstein J. Org. Chem. 2016, 12, 882–902, doi:10.3762/bjoc.12.87

• (sp3)–H bond has gained special attention, as in the works of Muler and Boléa [9], Flynn [10], Stattery [11] and their respective co-workers. The most selective copper carbenoids are those generated from chiral bis(oxazoline) ligands in the presence of copper(I) triflate (CuOTf) (Figure 3). The rhodium

• transformation was regio and stereoselective where the main product was trans-γ-lactam (56). The chiral rhodium complexes (S)-17, (S)-18 and (S)-23 were also evaluated and yielded similar regio- and diastereoselectivity, however, with lower enantioselectivity when compared to the bis(oxazoline)/CuCl2/NaBARF

• carbene, triplet carbene and carbenoids. Classification of the carbenoid intermediates by the electronic nature of the groups attached to the divalent carbene carbon. Chiral bis(oxazoline) ligands used in enantioselective copper carbenoid insertion. Chemical structures of complexes (R)-18 and (S)-18

Synthesis and in vitro cytotoxicity of acetylated 3-fluoro, 4-fluoro and 3,4-difluoro analogs of D-glucosamine and D-galactosamine

• Štěpán Horník,
• Lucie Červenková Šťastná,
• Petra Cuřínová,
• Jan Sýkora,
• Kateřina Káňová,
• Roman Hrstka,
• Ivana Císařová,
• Martin Dračínský and
• Jindřich Karban

Beilstein J. Org. Chem. 2016, 12, 750–759, doi:10.3762/bjoc.12.75

• acetal with acetic anhydride gave a mixture containing 1,2-oxazoline 41 as the main product (Scheme 5). The structure of oxazoline 41 was confirmed by single crystal X-ray diffraction analysis which also confirmed the retention of configuration during the preceding fluorine introduction. To prevent

• oxazoline formation, the order of reactions was reversed, and triethylsilyl triflate (TESOTf)-catalyzed [58] acetolysis of the 1,6-anhydro bridge in 19 gave 42 (Table 1) as a mixture of anomers from which the α-anomer crystallized. TESOTf as a catalyst for acetolysis gave better results than sulfuric acid

• 8, and oxazoline 41 was therefore tested for 24 h on the human prostate cancer PC-3 cell line, and human ovarian cancer A2780 cell line using the MTT assay, and the obtained IC50 values were compared with those obtained for cisplatin and 5-fluorouracil. All of the tested compounds induced only

Antibiotics from predatory bacteria

• Juliane Korp,
• María S. Vela Gurovic and
• Markus Nett

Beilstein J. Org. Chem. 2016, 12, 594–607, doi:10.3762/bjoc.12.58

• possess antioxidative properties and might thus confer resistance towards oxidative stress [63]. Structurally, the DKxanthenes harbor a hydrophilic asparagine moiety attached to a hydrophobic polyene chain bearing an additional oxazoline and pyrrol ring system. Their production seems to be universal among

Spiro-fused carbohydrate oxazoline ligands: Synthesis and application as enantio-discrimination agents in asymmetric allylic alkylation

• Jochen Kraft,
• Martin Golkowski and
• Thomas Ziegler

Beilstein J. Org. Chem. 2016, 12, 166–171, doi:10.3762/bjoc.12.18

• present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O

• benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as

• for metal-catalyzed asymmetric syntheses [16] we recently described the preparation of spiro-fused oxazoline ligands of type C from D-fructose [17]. We could demonstrate that our oxazoline ligands, in contrast to A, were able to form air and moisture-stable palladium complexes of type D upon reaction

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• , highlighting both the accomplishments and the future work needed in this important area. Throughout the discussion below, it is clear that there are privileged ligand architectures of these copper-catalyzed alkynylations. High enantioselectivities have been achieved with pyridine bis(oxazoline) (Pybox), bis

• (oxazoline) (Box), and Quinap-type ligands (Figure 1). Review Additions to iminium ions Although this review will focus on enantioselective additions to cyclic electrophiles, it is worth noting that the first enantioselective additions of chiral copper acetylides to imines or iminium ions utilized acyclic

Recent advances in copper-catalyzed asymmetric coupling reactions

• Fengtao Zhou and
• Qian Cai

Beilstein J. Org. Chem. 2015, 11, 2600–2615, doi:10.3762/bjoc.11.280

• of trans-4,5,9,10-tetrahydroxy-9,10-dihydrophenanthrene at room temperature (Scheme 4). In 1994, Meyers and Nelson [23][24] developed a copper-mediated asymmetric biaryl coupling with oxazoline as the chiral auxiliary to afford the biaryl-coupling products in high diastereomeric purity (dr = 93:7

• )hexopyranose derivatives. Preparation of 3,3’-disubstituted MeO-BIPHEP derivatives. Enantioselective synthesis of trans-4,5,9,10-tetrahydroxy-9,10-dihydrophenanthrene. Copper-catalyzed coupling of oxazoline-substituted aromatics to afford biaryl products with high diastereomeric purity. Total synthesis of O

Synthesis of D-fructose-derived spirocyclic 2-substituted-2-oxazoline ribosides

• Madhuri Vangala and
• Ganesh P. Shinde

Beilstein J. Org. Chem. 2015, 11, 2289–2296, doi:10.3762/bjoc.11.249

• Madhuri Vangala Ganesh P. Shinde Department of Chemistry, Indian Institute of Science Education and Research, Pune 411 008, India 10.3762/bjoc.11.249 Abstract The TMSOTf-mediated synthesis of β-configured spirocyclic 2-substituted-2-oxazoline ribosides was achieved using a “Ritter-like” reaction

• spirooxazolines are stable and were obtained in good yield with high stereoselectivity due to the conformational rigidity imparted by the 3,4-isopropylidene group. Keywords: fructose; oxazoline; riboside; Ritter reaction; spiro; Introduction 2-Oxazolines represent a unique class of 5-membered heterocyclic

• compounds with a wide range of applications spanning different chemistry disciplines. 2-Oxazoline derivatives are extensively studied due to their presence in numerous bioactive natural products [1][2][3] and synthetic drugs with anticancer, antibiotic, antidiabetic, and antifungal properties (Figure 1, 1–4

Recent advances in copper-catalyzed C–H bond amidation

• Jie-Ping Wan and
• Yanfeng Jing

Beilstein J. Org. Chem. 2015, 11, 2209–2222, doi:10.3762/bjoc.11.240

• or secondary sulfonamides 15 with the assistance of 1,10-phenanthroline as a ligand (Scheme 3). Notably, the asymmetric version of a similar amidation had been previously achieved by Clark et al. via copper catalysis in the presence of a chiral oxazoline ligand, which allowed the synthesis of

• alkene substrates were systematically investigated by Chemler and co-workers. For example, they [67] developed the copper-catalyzed protocol for the sulfonamidation reaction of alkenes 68 via direct C–H activation to provide N-vinylsufonamides 69 in the presence of an oxazoline ligand. On the other hand

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• , heteroaryl, and alkyl, etc. to produce α,β-unsaturated acylimidazolidinones 215. Next, the Evan’s asymmetric DA methodology involving a [4 + 2] cycloaddition of chiral bis(oxazoline) in the presence of Cu(OTf)2 was employed to furnish the required norbornene system 216. Later, it was converted into a lactam

Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

• Sara J. Krivickas,
• Chiho Hashimoto,
• Junya Yoshida,
• Akira Ueda,
• Kazuyuki Takahashi,
• John D. Wallis and
• Hatsumi Mori

Beilstein J. Org. Chem. 2015, 11, 1561–1569, doi:10.3762/bjoc.11.172

• -TTF (2), TTF (3), BEDT-TTF (4), EDT-TTF-methyl-oxazoline 5, and trans-dimethyl-EDT-TTF (6). (a) Crystal structure, (b) θ21-type donor arrangement of molecules A and A’ [(S,S) and (R,R)-2 indicated by red and blue with charge of +0.59(8)], B and B’ [(R,R) and (S,S)-2, blue and red with +0.23(7)], and C

New palladium–oxazoline complexes: Synthesis and evaluation of the optical properties and the catalytic power during the oxidation of textile dyes

• Rym Hassani,
• Mahjoub Jabli,
• Yakdhane Kacem,
• Jérôme Marrot,
• Damien Prim and
• Béchir Ben Hassine

Beilstein J. Org. Chem. 2015, 11, 1175–1186, doi:10.3762/bjoc.11.132

• University of Versailles Saint-Quentin-en-Yvelines, Institut Lavoisier de Versailles, UMR CNRS 8180, 45, avenue des Etats-Unis, 78035 Versailles, France 10.3762/bjoc.11.132 Abstract The present paper describes the synthesis of new palladium–oxazoline complexes in one step with good to high yields (68–95

• used for the total synthesis of natural products and nanocompounds [5]. It is only since 1986 that oxazoline-based ligands have been utilized in asymmetric catalysis. This initiated considerable research activity in this field and triggered the synthesis of numerous chiral ligands containing at least

• one oxazoline ring [6]. Oxazoline units are expected to readily coordinate to a metal center and have been shown to bind a wide range of transition metals [7]. The wide variety of ligands with one or more oxazoline rings incorporating different heteroatoms, additional chiral groups, and specific

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

• Flavia Pop and
• Narcis Avarvari

Beilstein J. Org. Chem. 2015, 11, 1105–1111, doi:10.3762/bjoc.11.124

• ethylenedithiotetrathiafulvalene-oxazoline (EDT-TTF-Ox) donors [5][6], due to a structural disorder effect [7]. Evidence was thus provided, and confirmed later on with a second complete series of conducting salts based on the same donors [8], that the presence of chiral centers can modulate the structural disorder of radical

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• and co-workers developed various N-sulfinyl homoallylic amines (76) [160] and N-cinnamyl sulfonamides (77) [161] ligands for the rhodium-catalyzed asymmetric 1,4-arylation of a variety of α,β-unsaturated carbonyl compounds. Finally, in 2012, Franzén and co-workers designed an indole-olefin-oxazoline

• either a Sc(OTf)3–3,3′-bis(diethylaminomethyl)-1,1′-bi-2-naphthol complex (85) or Cu(OTf)2–(S,S)-2,2′-isopropylidene-bis(4-tert-butyl-2-oxazoline) complex (86) (Figure 6). The latter bis(oxazoline) and its derivatives have become common chiral ligands in Lewis acid-mediated reactions [179]. The Evans

• group has developed several methods for Diels–Alder and aldol reactions that employed chiral bis(oxazoline) copper(II) complexes [180]. Starting in 1999, Evans and co-workers published a series of papers which reported the Mukaiyama–Michael addition to various α,β-unsaturated Michael acceptors [181][182

Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space

• Simon A. Herbert,
• Laura J. van Laeren,
• Dominic C. Castell and
• Gareth E. Arnott

Beilstein J. Org. Chem. 2014, 10, 2751–2755, doi:10.3762/bjoc.10.291

• Simon A. Herbert Laura J. van Laeren Dominic C. Castell Gareth E. Arnott Department of Chemistry and Polymer Science, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa 10.3762/bjoc.10.291 Abstract The diastereoselective oxazoline-directed lithiation of calix[4]arenes is

• reported with diastereoselective ratios of greater than 100:1 in some instances. Notably, it has been found that the opposite diastereomer can be accessed via this approach merely through the choice of an alkyllithium reagent. The inherently chiral oxazoline calix[4]arenes have also been preliminarily

• examined as ligands in the palladium-catalyzed Tsuji–Trost allylation reaction, returning results comparable to their planar chiral ferrocene counterparts pointing towards future application of these types of compounds. Keywords: calix[4]arene; inherently chiral; ortholithiation; oxazoline; Tsuji–Trost

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• the van Leusen reaction from trans-3-(2-vinylphenyl)acrylaldehyde which is prepared from o-vinylbenzaldehyde and (formylmethylene)triphenylphosphorane. The 4- and 5-(2-vinylstyryl)oxazoles afford, by photochemical intramolecular cycloaddition, diverse fused oxazoline-benzobicyclo[3.2.1]octadienes

• , which are identified and characterized by spectroscopic methods. The photoproducts formed are relatively unstable and spontaneously or on silica gel undergo oxazoline ring opening followed by formation of formiato- or formamido-benzobicyclo[3.2.1]octenone derivatives. On irradiation of 4-(2-vinylstyryl

• intramolecular photocycloaddition to diverse fused tetracyclic oxazoline compounds which further spontaneously or during the work-up procedure hydrolyze to benzobicyclo[3.2.1]octenone derivatives. This is a new method for the synthesis of functionalized benzobicyclo[3.2.1]octenes. Results and Discussion cis

Rational design of cyclopropane-based chiral PHOX ligands for intermolecular asymmetric Heck reaction

• Marina Rubina,
• William M. Sherrill,
• Alexey Yu. Barkov and
• Michael Rubin

Beilstein J. Org. Chem. 2014, 10, 1536–1548, doi:10.3762/bjoc.10.158

• Abstract A novel class of chiral phosphanyl-oxazoline (PHOX) ligands with a conformationally rigid cyclopropyl backbone was synthesized and tested in the intermolecular asymmetric Heck reaction. Mechanistic modelling and crystallographic studies were used to predict the optimal ligand structure and helped

• regio- and enantioselectivities. On the other hand, superior results were obtained using chiral ligands of the P,N-type [15][41][42][43][44]. Particularly, excellent enantioselectivities were achieved using different variations of phosphanyl-oxazoline (PHOX) ligands [45][46][47][48][49][50][51][52

• substrates [59]. A highly efficient asymmetric arylation in the presence of sugar-derived phosphite-oxazoline ligands was reported by Diéguez and Pàmies [47][48]. PHOX ligands are very appealing due to their high catalytic potential and modular design, which permits easy preparation of a series of analogues

Design, automated synthesis and immunological evaluation of NOD2-ligand–antigen conjugates

• Marian M. J. H. P. Willems,
• Gijs G. Zom,
• Nico Meeuwenoord,
• Ferry A. Ossendorp,
• Herman S. Overkleeft,
• Gijsbert A. van der Marel,
• Jeroen D. C. Codée and
• Dmitri V. Filippov

Beilstein J. Org. Chem. 2014, 10, 1445–1453, doi:10.3762/bjoc.10.148

• attached to the anomeric center of the glucosamine moiety using oxazoline 6 [37][38][39]. Deacetylation and subsequent installation of the benzylidene protective group then gave alcohol 9. Coupling of 9 with (S)-2-chloropropanoic acid in the presence of sodium hydride resulted in the formation of protected

Synthesis of 1-[bis(trifluoromethyl)phosphine]-1’-oxazolinylferrocene ligands and their application in regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates

• Zeng-Wei Lai,
• Rong-Fei Yang,
• Ke-Yin Ye,
• Hongbin Sun and
• Shu-Li You

Beilstein J. Org. Chem. 2014, 10, 1261–1266, doi:10.3762/bjoc.10.126

• branched monosubstituted allyl acetate favoring the branched products. However, linear products were favored when the linear allyl substrates were employed [23][24]. The chiral oxazoline–phosphite ligands introduced by Pfaltz and coworkers proved to be highly efficient for regio- and enantiocontrol in the

• an elegant synthesis of bis(perfluoroalkyl)phosphine-oxazoline ligands where small but strongly electron-withdrawing substituents were introduced at the phosphorus [34]. 1,2-Ferrocene based P,N-ligands were synthesized and gave excellent regio- and enantioselectivities in the Pd-catalyzed allylic

• ). Good regioselectivity (b/l: 81/19) was obtained with 2-buten-3-yl carbonate as a substrate (entry 14, Table 2). We conducted some control experiments to probe the effect of the bis(trifluoromethyl) group in the ligands (Scheme 3). With ferrocence-based biphenyl phosphine-oxazoline L2 as the ligand, the

Organocatalytic asymmetric fluorination of α-chloroaldehydes involving kinetic resolution

• Kazutaka Shibatomi,
• Takuya Okimi,
• Yoshiyuki Abe,
• Akira Narayama,
• Nami Nakamura and
• Seiji Iwasa

Beilstein J. Org. Chem. 2014, 10, 323–331, doi:10.3762/bjoc.10.30

• α-chloro-α-fluoro-β-keto esters via the sequential chlorination–fluorination of β-keto esters with the Cu(II) complex of SPYMOX [9], a spiro chiral oxazoline ligand developed by our research group [9][10][11][12]. In that study, we succeeded in determining the absolute stereochemistry of the α

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• reaction conditions showed that cesium fluoride proved the best base. PhI(OAc)2 was the preferred oxidant over other hypervalent iodine compounds or sources of F+ or CF3+; additionally, the presence of a bis(oxazoline) as a ligand was beneficial to the reaction, as well as that of TEMPO to prevent