Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins

• Robert Hilgraf,
• Nicole Zimmermann,
• Lutz Lehmann,
• Armin Tröger and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1256–1264, doi:10.3762/bjoc.8.141

• 4-H and 7a-H. In summary, we have completed the first enantioselective synthesis of all eight stereoisomers of trans-fused iridomyrmecins, starting from either of the cheaply available enantiomers of limonene. The acetate 4 is the decisive intermediate, and key reaction steps are two stereoselective

Algicidal lactones from the marine Roseobacter clade bacterium Ruegeria pomeroyi

• Ramona Riclea,
• Julia Gleitzmann,
• Hilke Bruns,
• Corina Junker,
• Barbara Schulz and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2012, 8, 941–950, doi:10.3762/bjoc.8.106

• mass spectra and unambiguously verified by the synthesis of reference compounds. An enantioselective synthesis of two exemplary lactones was performed to establish the enantiomeric compositions of the natural products by enantioselective GC–MS analyses. The lactones were subjected to biotests to

• . pomeroyi, an enantioselective synthesis of 7 and 8 was carried out (Scheme 2). For this purpose the lactone (2S,3R,4R)-2,4-dimethyl-5-oxotetrahydrofuran-3-yl 2-ethylpentanoate (18), a derivative of the antimycin degradation product blastmycinone, which has recently been obtained in an enantioselective

• (w), 733 (w), 583 (w) cm−1; UV–vis λmax (log ε): 238 (1.30), 233 (0.92) nm. Enantioselective synthesis of (2R,4S)-7 and (2S,4S)-8. Treatment of (2S,3R,4R)-18 (15 mg, 0.06 mmol; its synthesis is published elsewhere [29]) with Et3N (12 mg, 0.12 mmol, 2 equiv) in dry CH2Cl2 (1 mL) for 1 h at room

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• -unsaturated aldehydes [18], the enantioselective synthesis of cyclopentenes from α,β-unsaturated aldehydes and α,β-unsaturated ketones [19], and the preparation of cyclopentanes through the reaction of enals and β,γ-unsaturated α-ketoesters [20]. Discussion Recently, Rovis et al. reported that the acetate

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers

• Abigail Page and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1327–1333, doi:10.3762/bjoc.7.156

• on the enantioselective synthesis of diaryl ethers (a potential new class of chiral ligand having a structure related to the wide bite angle diphosphine DPEPhos) by biocatalytic oxidation or reduction, and which made use of desymmetrisation of a “pro-atropisomeric” substrate 4 to achieve the required

• stereochemical course of the lithiation–substitution reactions have been elucidated, and further work remains to exploit this transformation for the potential synthesis of new classes of chiral ligands [12]. Desymmetrising metallation for the enantioselective synthesis of atropisomers. Benzylic lithiation of a

• diaryl ether. Benzylic metallation of a diaryl ether α to a carbamate. Diastereo- and enantioselective synthesis of atropisomeric ethers by benzylic lithiation. Atroposelective stannylation. Stereospecific tin–lithium exchange/quench reactions. Proposed stereochemical pathway. Yields and selectivities in

Synthesis of enantiomerically enriched (R)-¹³C-labelled 2-aminoisobutyric acid (Aib) by conformational memory in the alkylation of a derivative of L-alanine

• Stephen P. Fletcher,
• Jordi Solà,
• Dean Holt,
• Robert A. Brown and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1304–1309, doi:10.3762/bjoc.7.152

• oligomers. We now report in detail a practical method for the enantioselective synthesis and enantiomeric assignment of a derivative of (R)-1*. Results and Discussion L-Alanine hydrochloride 2 was converted to its sodium salt either in situ with two equiv sodium hydride, or (preferably, and more

Asymmetric Au-catalyzed cycloisomerization of 1,6-enynes: An entry to bicyclo[4.1.0]heptene

• Alexandre Pradal,
• Chung-Meng Chao,
• Patrick Y. Toullec and
• Véronique Michelet

Beilstein J. Org. Chem. 2011, 7, 1021–1029, doi:10.3762/bjoc.7.116

• comprehensive study on gold-catalyzed enantioselective synthesis of bicyclo[4.1.0]heptenes, focusing on the scope and limitations of such systems. Results and Discussion Optimization of the catalytic system Based on our ongoing program on asymmetric gold catalysis [46][49][50][51][52], and on literature reports

Chiral gold(I) vs chiral silver complexes as catalysts for the enantioselective synthesis of the second generation GSK-hepatitis C virus inhibitor

• María Martín-Rodríguez,
• Carmen Nájera,
• José M. Sansano,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2011, 7, 988–996, doi:10.3762/bjoc.7.111

• have been used for the synthesis of a similar key molecule 5b (R1 = t-Bu, 88% ee), but the overall synthesis of the antiviral drug was not reported [27][28]. In this article, we describe the full study concerning the enantioselective synthesis of product 5b using silver(I) or gold(I) complexes

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• bond. Liu et al. has developed two highly stereoselective cationic gold(I)-catalyzed tandem cyclization reactions of alkynylindoles 322 [160]. The reaction proceeds with remarkable retention of chirality and allows the efficient enantioselective synthesis of polycyclic indolines 327 from the

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• in a formal enantioselective synthesis of frondosin A, a marine norsesquiterpenoid with promising biological activities (Scheme 28) [48]. Treatment of pivalate 95 and 6,6-dimethyl-1-vinylcyclohexene (96) with (S)-MeO-DTBM-BIPHEP-gold(I) complex afforded the corresponding bicyclic cycloheptenyl

• pivalate quantitatively. In situ hydrolysis and subsequent equilibration with NaOMe/MeOH yielded thermodynamically favored ketone 97 in 68% yield and >90% ee. Since this bicyclic enone has been recently elaborated to frondosins A and B [60][61] this approach represents a streamlined formal enantioselective

• synthesis of both molecules. In addition, 3- and 1-substituted cyclopropyl propargylic acetates 98 and 99 have also been intensively studied and provide access to 5- and 6-membered ring enones, respectively (Scheme 29) [62][63][64]. In the former substrates, experimental as well as computational evidence

A racemic formal total synthesis of clavukerin A using gold(I)-catalyzed cycloisomerization of 3-methoxy-1,6-enynes as the key strategy

• Jae Youp Cheong and
• Young Ho Rhee

Beilstein J. Org. Chem. 2011, 7, 740–743, doi:10.3762/bjoc.7.84

• compatible with the acid-sensitive functional group. Further application of the gold(I)-catalyzed cycloisomerization reaction of 3-methoxy-1,6-enynes to the enantioselective synthesis of more structurally complex cycloheptane natural products is in progress, and will be reported in due course. Retrosynthetic

Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2011, 7, 601–605, doi:10.3762/bjoc.7.70

• allene-yne that generates a chiral non-racemic spirooxindole from a chiral non-racemic allene. Furthermore, this reaction could also be applicable in the enantioselective synthesis of natural products that contain a spirooxindole core, such as welwitindolinone A isonitrile. We are currently working to

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

• Carolin Fischer and
• Burkhard Koenig

Beilstein J. Org. Chem. 2011, 7, 59–74, doi:10.3762/bjoc.7.10

• ,5S)-3,6-diazabicyclo[3.2.0]heptane 10. The use of Cs2CO3 instead of the conventional base t-BuONa increased the yield of 11 from 47% to 73% (Scheme 3) [52]. The enantioselective synthesis of A-366833 allowed large-scale preparation required for preclinical investigations. Oxcarbazepine (13, Trileptal

Achiral bis-imine in combination with CoCl₂: A remarkable effect on enantioselectivity of lipase-mediated acetylation of racemic secondary alcohol

• K. Arunkumar,
• M. Appi Reddy,
• T. Sravan Kumar,
• B. Vijaya Kumar,
• K. B. Chandrasekhar,
• P. Rajender Kumar and
• Manojit Pal

Beilstein J. Org. Chem. 2010, 6, 1174–1179, doi:10.3762/bjoc.6.134

• preliminary results on the synthesis and identification of a novel ligand for this process (Scheme 1) and its application in the preparation of the known drug rivastigmine [14]. While the uses of bis-imine/transition-metal complexes have been reported for the enantioselective synthesis of chiral compounds [15

Enantioselective synthesis of tricyclic amino acid derivatives based on a rigid 4-azatricyclo[5.2.1.0^2,6]decane skeleton

• Matthias Breuning,
• Tobias Häuser,
• Christian Mehler,
• Christian Däschlein,
• Carsten Strohmann,
• Andreas Oechsner and
• Holger Braunschweig

Beilstein J. Org. Chem. 2009, 5, No. 81, doi:10.3762/bjoc.5.81

• β-turn-inducing building blocks in peptidomimetics and for chiral auxiliaries in asymmetric organocatalysis. Keywords: amino acid; enantioselective synthesis; norbornane; polycyclic compounds; pyrrolidine; Introduction Unnatural amino acids with a rigid bowl-shaped backbone have received

• peptide building blocks and as bifunctional organocatalysts. In this paper we report on the first enantioselective synthesis of 7 and 8, which was achieved via the chiral ketone 9 as the key intermediate. Results and Discussion The key intermediate, the tricyclic amino ketone 9, was first prepared in

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• variously distributed around the molecular core, allows us to extend our knowledge of the molecular origin of the chirality amplification in liquid crystals. Results and Discussion The enantioselective synthesis as well as the configuration assignment of enantiopure dihydro[5]helicene quinones or

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• sordarin and sordaricin Narasaka et al. published a synthesis of racemic sordaricin in 2004 [16], and 2 years later, they described the first enantioselective synthesis of (−)-sordarin [17]. The retrosynthetic plan is outlined in Scheme 7. (−)-Sordarin would result through a β-selective glycosylation

• believed to involve single-electron oxidation of the cyclopropanol, fragmentation of a transient radical cation, and diastereoselective radical cyclization. In the enantioselective synthesis, this transformation was more efficiently achieved by treatment of enantioenriched 41b with the AgNO3-ammonium

• (Scheme 9). The latter was directly converted to a β-ketoester by reaction with ethyl diazoacetate in the presence of SnCl2. A final Knoevenagel cyclization afforded substance 45. The enantioselective synthesis implemented an improved procedure that relied on alkylation of the metallohydrazone of 43 with

Control of asymmetric biaryl conformations with terpenol moieties: Syntheses, structures and energetics of new enantiopure C₂-symmetric diols

• Y. Alpagut,
• B. Goldfuss and
• J.-M. Neudörfl

Beilstein J. Org. Chem. 2008, 4, No. 25, doi:10.3762/bjoc.4.25

• ] are often employed as chiral ligands in enantioselective synthesis. We recently reported the synthesis and the X-ray crystal structure of (M)-BIFOL [7] (biphenyl-2,2′-bisfenchol, Scheme 1) and its derivatives [8][9][10][11]. (M)-BIFOL exhibits, in a similar way as BINOLs, a flexible biaryl axis with M

Facile synthesis of two diastereomeric indolizidines corresponding to the postulated structure of alkaloid 5,9E- 259B from a Bufonid toad (Melanophryniscus)

• Angela Nelson,
• H. Martin Garraffo,
• Thomas F. Spande,
• John W. Daly and
• Paul J. Stevenson

Beilstein J. Org. Chem. 2008, 4, No. 6, doi:10.1186/1860-5397-4-6

• indolizidines are known [2]. Thus, in analogy to such 5,9Z indolizidines it might be anticipated that for the 5,9E indolizidines the stereochemistry at C9 will also be R. We now report an enantioselective synthesis of the tentative structure postulated for ent-indolizidine 5,9E-259B, which is outlined in Scheme

Analogues of amphibian alkaloids: total synthesis of (5R,8S,8aS)-(−)-8-methyl- 5-pentyloctahydroindolizine (8-epi-indolizidine 209B) and [(1S,4R,9aS)-(−)-4-pentyloctahydro- 2H-quinolizin- 1-yl]methanol

• Joseph P. Michael,
• Claudia Accone,
• Charles B. de Koning and
• Christiaan W. van der Westhuyzen

Beilstein J. Org. Chem. 2008, 4, No. 5, doi:10.1186/1860-5397-4-5

• development of enaminones as versatile intermediates for the synthesis of alkaloids and other nitrogen-containing heterocycles. In this paper we describe the enantioselective synthesis of indolizidine and quinolizidine analogues of bicyclic amphibian alkaloids via pyrrolidinylidene- and piperidinylidene

• )-3-{benzyl[(1R)-1-phenylethyl]amino}octanoate (+)-14 was achieved in 14 steps and an overall yield of 20.4%. Conclusion The methodology reported in this article was successfully applied to the enantioselective synthesis of the title compounds. It paves the way for the total synthesis of a range of

• total synthesis of (−)-indolizidine 209B 8. As a postscript to the above synthesis, we have now completed an enantioselective synthesis (Scheme 2) of the indolizidine analogue of 8, viz. (5R,8S,8aS)-8-epi-indolizidine 209B (−)-9, which we had previously made as a racemate [13]. Intermediate (−)-20 was

Large- scale ruthenium- and enzyme- catalyzed dynamic kinetic resolution of (rac)-1-phenylethanol

• Krisztián Bogár,
• Belén Martín-Matute and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2007, 3, No. 50, doi:10.1186/1860-5397-3-50

• natural products. [1][2][3][4] A few methods have been developed for the enantioselective synthesis of chiral alcohols including catalytic asymmetric hydrogenation [5][6][7][8][9][10][11][12][13][14] and enantioselective hydride addition [15][16] of prochiral ketones, asymmetric dialkylzinc addition to

Synthesis of crispine A analogues via an intramolecular Schmidt reaction

• Ajoy Kapat,
• Ponminor Senthil Kumar and
• Sundarababu Baskaran

Beilstein J. Org. Chem. 2007, 3, No. 49, doi:10.1186/1860-5397-3-49

• indolizidine skeleton using an epoxide initiated electrophilic cyclization of azide as a key step. This novel methodology has been efficiently applied in the stereo- and enantioselective synthesis of indolizidine 167B and 209D (Scheme 1). [16][17][18] Results and discussion In 2002, a new indolizidine alkaloid

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis

• Roger Hunter,
• Sophie C. M. Rees-Jones and
• Hong Su

Beilstein J. Org. Chem. 2007, 3, No. 38, doi:10.1186/1860-5397-3-38

• aldol strategy for the C-8 and C-8a stereogenic centres of castanospermine is presented using silyloxypyrrole chemistry. The results suggest that a full enantioselective synthesis can be realized provided that C-1 functionalisation is accomplished early in the synthesis, post-coupling. Background N

• destabilization of the intermediate oxocarbenium ion by the adjacent α-ammonium cation. Conclusion In summary, the present work has laid the foundation for a full enantioselective synthesis of castanospermine using a C-8/C-8a disconnection strategy. Future work will focus on C-1 transformation earlier in the

A convenient allylsilane- N-acyliminium route toward indolizidine and quinolizidine alkaloids

• Roland Remuson

Beilstein J. Org. Chem. 2007, 3, No. 32, doi:10.1186/1860-5397-3-32

• trimethylsilylmethylmagnesium chloride addition to ethyl (S)-3-hydroxybutanoate as we described. [50] The first three steps of the enantioselective synthesis were those previously described for the synthesis of racemic compounds (vide supra). Condensation of alcohol 32 with glutarimide under Mitsunobu conditions led to

• constitute the first total synthesis of naturally occurring (-)-lasubine II and (+)-subcosine II and unambiguously establish their absolute configuration as 2S,4S,10S. Allylsilane-N-acyliminium cyclisation. Enantioselective synthesis of (-)-indolizidine 167B by intramolecular allylsilane-N-acyliminium

• by reduction with LiAlH4 of indolizidinones 26. Access to (-)-dendroprimine by catalytic hydrogenation of indolizidinones 26. Synthesis of (±)-myrtine and (±)-epimyrtine. Enantioselective synthesis of (+)-myrtine and (-)-epimyrtine. Synthesis of (±)-lasubines I and II and (±)-2-epilasubine II

The first salen- type ligands derived from 3',5'-diamino- 3',5'-dideoxythymidine and -dideoxyxylothymidine and their corresponding copper(II) complexes

• Daniel Koth,
• Michael Gottschaldt,
• Helmar Görls and
• Karolin Pohle

Beilstein J. Org. Chem. 2006, 2, No. 17, doi:10.1186/1860-5397-2-17

• of diimino functionalized ligands are often used as catalysts for a wide variety of reactions. Enantioselective synthesis has gained in importance in the last few years, and the development of chiral ligands has become an important field in organic chemistry. Nucleosides provide a stable scaffold