A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• substrate [36][37]. The activity and enantioselectivity achieved by proline in many cases is thought to be due to a templating effect of the OH group directing the aldehyde in a preferred position via hydrogen bonding [24][25]. It is still controversial whether oxazolidinone formation plays a pivotal role

• in-source fragmentation when slightly harsher ionization conditions are used. This fragmentation is in perfect accordance with the zwitterionic iminium structures II’ and III and can also be rationalized for the oxazolidinone alternative II’’, whereas it requires an additional hydrogen shift from the

• enamine structure II. On the other hand, the comparison with the fragmentation of the structurally related ion [II*b]+ (Figure 5b) is instructive. It doubtlessly possesses an enamine structure since it can neither form a zwitterionic iminium ion nor undergo lactonization to oxazolidinone II’’b because of

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• bearing a chiral oxazolidinone auxiliary, facile access to the cis-aziridine series was possible by using chiral chloroallyl phosphonamide 47a. Thus, the addition of the anion of 47a to tert-butylglyoxylate O-benzylamine (139) led to aziridine 140 as a single diastereomer. Ozonolysis followed by reductive

Amino acid motifs in natural products: synthesis of O-acylated derivatives of (2S,3S)-3-hydroxyleucine

• Oliver Ries,
• Martin Büschleb,
• Markus Granitzka,
• Dietmar Stalke and
• Christian Ducho

Beilstein J. Org. Chem. 2014, 10, 1135–1142, doi:10.3762/bjoc.10.113

• confirmes the stereocenters to have the proposed (2R,3S)-configuration. In their synthesis of (2S,3S)-3-hydroxyleucine, Zhu and co-workers cyclized amino alcohol 5 towards an oxazolidinone, with the carbonyl group simultaneously providing O- and N-protection [32]. Removal of this protecting group required

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines – development of a phosphite-driven cyclodehydration

• Peter H. Huy,
• Julia C. Westphal and
• Ari M. P. Koskinen

Beilstein J. Org. Chem. 2014, 10, 369–383, doi:10.3762/bjoc.10.35

• –4:1 syn/anti. The slightly diminished yield of 9c (74–77%) compared to 9a and 9b (85–93%) is rationalized by formation of the oxazolidinone 10c as sideproduct. This cyclic carbamate results from the condensation of the alcoholate moiety of II with the Cbz-function passing the syn-periplanar

• ), Boc2O (1d). Synthesis of hydroxy ketones 7 (R = Me (a), Bn (b), Ph (c) and EtSMe (d); PG = Cbz (a–c), Boc (d)). Synthesis of amides 5e and 5f and ketone 7e. Synthesis of amino alcohols syn-9a–d and oxazolidinone 10a. (for 7a–c conditions A: H2 (1 atm), Pd/C, HCl, MeOH (THF/MeOH 1:1), rt, 3 h; for 7d

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes

• Ludovic Eberlin,
• Fabien Tripoteau,
• François Carreaux,
• Andrew Whiting and
• Bertrand Carboni

Beilstein J. Org. Chem. 2014, 10, 237–250, doi:10.3762/bjoc.10.19

• -component adducts were isolated in good yields up to 92%. A single diastereomer was detected with maleimides; the diastereoselectivity being lower with methyl acrylate and vinyl oxazolidinone (Scheme 7). A one-pot, palladium-mediated cycloisomerization of ene-ynes 5 was applied to the synthesis of the

Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions

• Quynh Pham Bao Nguyen and
• Taek Hyeon Kim

Beilstein J. Org. Chem. 2013, 9, 2113–2119, doi:10.3762/bjoc.9.248

• ]. Additionally, in the solid phase asymmetric alkylation reactions, in which Evans' 2-oxazolidinone chiral auxiliaries were used, the yield and stereoselectivity were too dependent on the base, reaction time, and supported resins. As an example, the base-catalyzed epimerization of the chiral center was

• than that in the solution phase (89% de) [27] due to the sterical hindrance of the polymeric support. While the most extensively explored Evans' 2-oxazolidinone chiral auxiliary required a complicated linker [15] and solid supports [14], as well as special treatment, in which the excess base

Synthesis of enantiomerically pure (2S,3S)-5,5,5-trifluoroisoleucine and (2R,3S)-5,5,5-trifluoro-allo-isoleucine

• Holger Erdbrink,
• Elisabeth K. Nyakatura,
• Susanne Huhmann,
• Ulla I. M. Gerling,
• Dieter Lentz,
• Beate Koksch and
• Constantin Czekelius

Beilstein J. Org. Chem. 2013, 9, 2009–2014, doi:10.3762/bjoc.9.236

• sodium cyanide to afford nitrile 3. Acid hydrolysis of 3 provided the enantiomerically pure carboxylic acid (R)-4 [19], which was then coupled to the oxazolidinone via the mixed anhydride (Scheme 1). With N-acyloxazolidinone 5 in hand, the optically active fluorinated α-amino acids (L-5,5,5

Regio- and stereoselective carbometallation reactions of N-alkynylamides and sulfonamides

• Yury Minko,
• Morgane Pasco,
• Helena Chechik and
• Ilan Marek

Beilstein J. Org. Chem. 2013, 9, 526–532, doi:10.3762/bjoc.9.57

• preformed organocopper species (Table 2, entries 7–10) [25]. Carbocupration of cyclic N-alkynylcarbamate (chiral oxazolidinone moiety) Recently, our group was particularly interested in the carbometallation reaction of ynamides bearing chiral cyclic carbamates 7, particularly the Evans's oxazolidinone [27

• carbocupration reaction is again at the center of interest but this time for the regioselective addition of organocopper derivatives to various ynamide species. Particularly interesting is the carbocupration of N-alkynyl carbamates 7, bearing Evans’s oxazolidinone chiral auxiliary, which leads to the formation

Development of peptidomimetic ligands of Pro-Leu-Gly-NH₂ as allosteric modulators of the dopamine D₂ receptor

• Swapna Bhagwanth,
• Ram K. Mishra and
• Rodney L. Johnson

Beilstein J. Org. Chem. 2013, 9, 204–214, doi:10.3762/bjoc.9.24

• highly moisture-labile oxazolidinone 30 of Seebach's “self-regeneration of chirality” methodology [47]. Stereoselective alkylation of 30 provided alkylated oxazolidinone 31 and cleavage of this N,O-acetal provided α-alkylated proline 32, which when Boc-protected gave 33. The formation of 34a and 34b was

• ) oxidative cleavage of the double bond with OsO4/NaIO4, and (3) hydrogenolysis of the benzyl ester [36][48]. Although the Seebach methodology provides a highly stereoselective way to α-alkylated prolines, there are several shortcomings to the originally developed protocols [47]. In the oxazolidinone

• formation reaction, these shortcomings include the need for a large excess of the costly pivalaldehyde, long condensation reaction times of 3–4 days, and issues surrounding the isolation and handling of the moisture-sensitive oxazolidinone. By replacing pentane (capable of forming a 2% azeotrope with water

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• preferred TS-C, because it yields the more stable oxazolidinone [91]. Figure 21 shows that the enaminocarboxylate 33− reacts 50 to 60 times faster with benzhydrylium ions than pyrrolidinocyclohexene 36 and even 800 to 900 times faster than the methyl ester 37 [92]. We consider the high rates of the

Electrochemical generation of 2,3-oxazolidinone glycosyl triflates as an intermediate for stereoselective glycosylation

• Toshiki Nokami,
• Akito Shibuya,
• Yoshihiro Saigusa,
• Shino Manabe,
• Yukishige Ito and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2012, 8, 456–460, doi:10.3762/bjoc.8.52

• , Wako, Saitama 351-0198, Japan 10.3762/bjoc.8.52 Abstract Glycosyl triflates with a 2,3-oxazolidinone protecting group were generated from thioglycosides by low-temperature electrochemical oxidation. The glycosyl triflates reacted with alcohols to give the corresponding glycosides β-selectively at low

• amino sugars [7][8], the selectivity highly depends on the nature of the glycosyl acceptors and reaction conditions. In the last decade, 2,3-oxazolidinone protected 2-amino-2-deoxy-glycosides have been developed as glycosyl donors for the stereoselective synthesis of amino sugars [9][10][11][12][13][14

• already reported a chemically generated glycosyl triflate equipped with an acetylated 2,3-oxazolidinone protecting group [11][19], we envisioned that the electrochemically generated glycosyl triflate with a 2,3-oxazolidinone protecting group could be a useful intermediate to reveal stereoselectivity in

Continuous proline catalysis via leaching of solid proline

• Suzanne M. Opalka,
• Ashley R. Longstreet and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2011, 7, 1671–1679, doi:10.3762/bjoc.7.197

• through a column of solid proline, presumably forming a soluble oxazolidinone intermediate. This transports a catalytic amount of proline from the packed-bed into the reactor coil for subsequent combination with a solution of nitrosobenzene, affording the desired optically active α-aminooxy alcohol after

• formation of the active enamine intermediate through breakdown of the putative oxazolidinone intermediate: A substrate-dependent model. Here, we report that a packed-bed of solid proline can be used to create a homogeneous catalyst, and we use this system to perform continuous α-aminoxylations. Not only do

• the flow of a combination of solvents, reactants and cocatalysts through the packed-bed would produce the active, homogeneous, oxazolidinone catalyst. To test our hypothesis, we used a Vapourtec R series reactor system [51] consisting of HPLC pumps for solvent and reagent inputs, a low-temperature

Continuous-flow enantioselective α-aminoxylation of aldehydes catalyzed by a polystyrene-immobilized hydroxyproline

• Xacobe C. Cambeiro,
• Rafael Martín-Rapún,
• Pedro O. Miranda,
• Sonia Sayalero,
• Esther Alza,
• Patricia Llanes and
• Miquel A. Pericàs

Beilstein J. Org. Chem. 2011, 7, 1486–1493, doi:10.3762/bjoc.7.172

• conversion versus time data for propanal; see Table 1, entry 1). Although not conclusive, these data suggest that the deactivation process is of a chemical nature, possibly due to the formation of an oxazolidinone between proline and the aldehyde [80][81][82], rather than a physical denaturation of the

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• palladium catalyzed reaction furnished oxazolidinone derivatives in similar yields. It was shown that, if one face of the double bond is blocked by substituents such as H or CN, the reaction also takes place. On the basis of these results, it was assumed that an antiperiplanar orientation of the metal and

• nucleophile is not necessary to form oxazolidinones. The metal is probably bonded to the allylic system from the same face as the nucleophile. Keywords: bicyclic endoperoxides; biscarbamates; oxazolidinone; Pd-catalyzed allylic reaction; singlet oxygen; Introduction Palladium-catalyzed carbon–carbon bond

• formation reactions in synthetic organic chemistry have attracted considerable attention in recent years [1]. Palladium-catalyzed allylation is also a particularly useful method for the activation of allylic substrates [2]. Trost et al. described a highly stereoselective synthesis of oxazolidinone 2

Application of the diastereoselective photodeconjugation of α,β-unsaturated esters to the synthesis of gymnastatin H

• Ludovic Raffier and
• Olivier Piva

Beilstein J. Org. Chem. 2011, 7, 151–155, doi:10.3762/bjoc.7.21

• dienoate chain. The configuration at the C-2 carbon atom of this precursor was controlled by using a diastereoselective alkylation of an acyl oxazolidinone. In some cases, a Claisen condensation took place and afforded a β-ketoamide in noticeable amounts diminishing the overall yield of the sequence [15

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• . Photooxygenation of trans-7,8-diacetoxy- and cis-7,8-dichlorobicyclo[4.2.0]octa-2,4-diene afforded the bicyclic endoperoxides. Reduction of the latter with thiourea followed by a Pd(0) catalyzed ionization/cyclization reaction gave the corresponding oxazolidinone derivatives. Oxidation of the double bond with

• KMnO4 or OsO4 followed by acetylation gave the acetate derivatives, the exact configuration of which was determined by spectroscopic methods. Hydrolysis of the oxazolidinone rings and removal of the acetate groups furnished the desired aminocyclitols. Keywords: aminocyclitol; cyclitols; endoperoxide

• added to a solution of 5 mol % of the catalyst, prepared by stirring a mixture of ligand (triisopropylphosphite) and tris(dibenzylideneacetone)–dipalladium-chloroform complex in THF. Subsequent purification by column chromatography gave oxazolidinone 13 in 48% yield (Scheme 1). The structure of 13 was

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

Ru-catalyzed dehydrogenative coupling of carboxylic acids and silanes - a new method for the preparation of silyl ester

• Guo-Bin Liu and
• Hong-Yun Zhao

Beilstein J. Org. Chem. 2008, 4, No. 27, doi:10.3762/bjoc.4.27

• , hexamethyldisilazane, aminosilanes, N-trimethylsilylalkanamines, N-trimethylsilyl-2-oxazolidinone, N-trimethylsilylacetamide, or trialkylsilyl 2-methallylprop-2-ene-1-sulfinates have been extensively utilized for the transformation of carboxylic acids into the desired silyl esters [28][29][30][31][32][33][34][35][36