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

• particle size: 0.035–0.070 mm). NMR spectra were recorded on a Bruker Avance 300. FAB mass spectra were measured with a Micromass: ZabSpec. The enantiomeric excess of products was determined by chiral HPLC analysis in comparison with authentic racemic material. HPLC measurements were performed using

A novel asymmetric synthesis of cinacalcet hydrochloride

• Veera R. Arava,
• Laxminarasimhulu Gorentla and
• Pramod K. Dubey

Beilstein J. Org. Chem. 2012, 8, 1366–1373, doi:10.3762/bjoc.8.158

• of 73:27 (chiral HPLC analysis). From this crude mixture, 4a was isolated in pure form by recrystallization from 10% ethyl acetate–hexanes in 68% yield with 99.94% ee (Scheme 3). Malonic acid (13) was condensed with 8 and a catalytic amount of piperidine in pyridine under reflux to yield 3-(3

• were recorded on a Perkin-Elmer spectrophotometer as KBr pellets or neat. Analytical TLC is conducted on E-Merck 60 F254 aluminium-packed silica gel plates (0.2 mm). Developed plates were visualized under UV light or in an iodine chamber. Chiral HPLC analyses were recorded with on a Waters Alliance

Recyclable fluorous cinchona alkaloid ester as a chiral promoter for asymmetric fluorination of β-ketoesters

• Wen-Bin Yi,
• Xin Huang,
• Zijuan Zhang,
• Dian-Rong Zhu,
• Chun Cai and
• Wei Zhang

Beilstein J. Org. Chem. 2012, 8, 1233–1240, doi:10.3762/bjoc.8.138

• quinine ester C-1. Asymmetric fluorination of 1a.a Supporting Information Supporting Information File 374: Chiral HPLC chromatograms for fluorination products 2a–i. LC–MS, NMR spectra for fluorination products 2a–i and cinchona alkaloid derivatives C-1, C-2, C-3 and C-6. LC–MS spectra for 2h and HRMS

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• standard techniques (UV–vis, circular dichroism, chiral HPLC and NMR) has established that the chiral optical response differs greatly depending on the position of the sulfoxide group (C-2 or C-3). Cis isomers in both p-tolylsulfinyl azocompounds show an opposite arrangement of substituents around the N=N

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• present. Using this method it was possible to prepare chiral oxacalix[3]arenes incorporating t-Bu, iPr, Et or H in the para-position of the phenolic moieties, as seen in example 30 in Figure 11 [45]. The enantiomers can be separated by a chiral HPLC column and give opposite circular dichroic spectra, and

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

• . Reaction with 3-phenylpropionaldehyde through reactor setup. aIsolated yield, due to the instability of the aldehyde, the product was reduced in batch to the corresponding 2-aminoxy alcohol prior to isolation. bDetermined by chiral HPLC. Reaction with isovaleraldehyde through reactor setup. aIsolated yield

• , due to the instability of the aldehyde, the product was reduced in batch to the corresponding 2-aminooxy alcohol prior to isolation. bDetermined by chiral HPLC. Screening of the reactor setup. Screening of temperature and residence time. Supporting Information The Experimental Section describes

Asymmetric synthesis of quaternary aryl amino acid derivatives via a three-component aryne coupling reaction

• Elizabeth P. Jones,
• Peter Jones,
• Andrew J. P. White and
• Anthony G. M. Barrett

Beilstein J. Org. Chem. 2011, 7, 1570–1576, doi:10.3762/bjoc.7.185

• required constituent amino acid 11 or 10 was isolated in reasonable yields (Scheme 8). Chiral HPLC analysis confirmed the expected high enantioselectivity of these esters. These results are promising, as they demonstrate that if the aryl group is derived from a less sterically hindered benzyne precursor

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• -dimethylaniline and benzyl alcohol yielding (+)-10-F in 77% yield (84.9% ee by HPLC), whose configuration has already been established by correlation with 12-F. Comparison of the elution order on a chiral HPLC column with the (+)-sign of the optical rotation implied an (S)-configuration of this sample, and

Lithium phosphonate umpolung catalysts: Do fluoro substituents increase the catalytic activity?

• Anca Gliga,
• Bernd Goldfuss and
• Jörg M. Neudörfl

Beilstein J. Org. Chem. 2011, 7, 1189–1197, doi:10.3762/bjoc.7.138

• : Intramolecular O1–O2 distance 2.83 Å, 7: Intramolecular O1–O2 distance 2.81 Å, Figure 1 and Figure 2, respectively), are generated. Chiral HPLC and X-ray analyses revealed one pair of enantiomers for diol 6 and 7 (HPLC (Daicel-OD-H, 90:10 n-hexane/isopropanol; flow 0.5 mL/min): 6: tR1 = 10.4 min; tR2 = 13.2 min

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

• product 1, and other derivatives including compounds 2, was achieved in several steps using, as the key reaction, the silver(I) or lithium(I)-metalloazomethine ylide, under basic conditions, and tert-butyl acrylate. The enantiomeric samples were isolated by semi-preparative chiral HPLC [9][10]. The first

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

• Sebastian Schlecht,
• Walter Frank and
• Manfred Braun

Beilstein J. Org. Chem. 2011, 7, 615–621, doi:10.3762/bjoc.7.72

• boronate–amine complex 10 on the other hand, the racemization barrier of the latter was determined. For this purpose, a sample of the enantiomerically pure complex 10 was heated in n-decane at 60 °C, and the decay of the optical purity was followed by chiral HPLC. Thus, the racemization rate at 325.4 K was

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

• Lian-jun Liu,
• Feijun Wang,
• Wenfeng Wang,
• Mei-xin Zhao and
• Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

• solution of compound 11 (76.6 mg, 0.20 mmol) in DCM (0.6 mL) was added to the resulting solution and the mixture stirred at rt for 36 h. Column chromatography of the reaction mixture gave the desired product. The enantiomeric purity of the product was determined by chiral HPLC analysis. Monodentate NHCs

Supramolecular FRET photocyclodimerization of anthracenecarboxylate with naphthalene-capped γ-cyclodextrin

• Qian Wang,
• Cheng Yang,
• Gaku Fukuhara,
• Tadashi Mori,
• Yu Liu and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2011, 7, 290–297, doi:10.3762/bjoc.7.38

• of ee indicates a higher yield of first/second eluted enantiomer detected on the chiral HPLC analysis. These observations prompted us to design and synthesize a more rigidly capped 6A,6C-(2,6-naphthalenedicarboxyl)-γ-CD 6. This modification further enabled us to trigger the photocyclodimerization via

• the ee of chiral photodimers, both determined by chiral HPLC, are shown in Table 1. As a general tendency, the HH dimers were preferred by introducing the aromatic substituents. Thus, the HH/HT ratio was dramatically enhanced from 0.12 for native γ-CD to 0.4–1.0 for biphenyl- or naphthalene-modified γ

• . Photoirradiation was performed in a UNISOKU USP-203 cryostat with an appropriate interference filter for 300 nm or 360 nm. Irradiated samples were subjected to chiral HPLC analysis on a tandem column of Intersil ODS-2(GL Science) and Chiralcel OJ-R (Daicel) with a 36:64 mixture of acetonitrile and water as eluent

A two step synthesis of a key unit B precursor of cryptophycins by asymmetric hydrogenation

• Benedikt Sammet,
• Mathilde Brax and
• Norbert Sewald

Beilstein J. Org. Chem. 2011, 7, 243–245, doi:10.3762/bjoc.7.32

• catalyst [14][15] gave the anticipated methyl ester 4 (Scheme 1) in 97% yield with an ee exceeding 98% (determined by chiral HPLC). Hydrogenation of 10 with 10% Pd/C was envisaged to obtain rac-4 as a reference for the determination of the ee. Interestingly, due to this more reactive catalyst a complete

• , H2, MeOH, 16 h, (76%). Supporting Information Supporting Information File 44: Full experimental procedures and detailed analytical data for the synthesis of 10 and 4 including chiral HPLC spectra. Acknowledgements We wish to thank F. Mertink, K.-P. Mester and G. Lipinski for running the NMR spectra

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

• -ethyl-N-methylcarbamoyl chloride followed by reduction with NaBH4 (Scheme 3), was selected for our purpose. Subsequently, the enzymatic processes were carried out and the isolated reaction mixture was analysed by chiral HPLC. Initially, the CAL-B mediated acetylation of (RS)-4 was carried out in the

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• hours followed by crystallization from ether/hexane. That no racemization occurred during this process was demonstrated by conversion of the mandelic acid into methyl mandelate followed analysis by chiral HPLC (data presented in Supporting Information File 1), which gave an enantiomeric excess of 81

• Information Chiral GC traces for all chiral cyanohydrin acetates and chiral HPLC data for methyl mandelate. NMR spectra of cyanohydrins in the presence of mandelic acid. Additionally, all of the kinetic data used to determine the catalyst order, the activation parameters and construct the Hammett plot are

α,β-Aziridinylphosphonates by lithium amide-induced phosphonyl migration from nitrogen to carbon in terminal aziridines

• David. M. Hodgson and
• Zhaoqing Xu

Beilstein J. Org. Chem. 2010, 6, 978–983, doi:10.3762/bjoc.6.110

• excellent yield (89%), and without any degradation of enantiopurity (>99% ee, as determined by chiral HPLC analysis of the benzoyl derivative 17). Hydrogenolytic ring-opening of aziridinylphosphonates provides an attractive entry to α- or β-aminophosphonates [6]. α,β-Aziridinylphosphonates bearing a β-aryl

• -aminophosphonate (+)-18 [32][42] in 68% yield with >99% ee (determined by chiral HPLC analysis of the benzoyl derivative 19, Scheme 6). Conclusion In summary, lithiation-induced phosphonyl migration from nitrogen to carbon in terminal aziridines 1 effects simultaneous N-deprotection and accesses synthetically

Towards racemizable chiral organogelators

• Jian Bin Lin,
• Debarshi Dasgupta,
• Seda Cantekin and
• Albertus P. H. J. Schenning

Beilstein J. Org. Chem. 2010, 6, 960–965, doi:10.3762/bjoc.6.107

• that these hydrogen-bonded dimers or tetramers subsequently stack via π-π interaction and via van der Waals interactions into bundled fibers. Racemization The racemization of R-3 was investigated by chiral HPLC. After adding 1 equivalent of DBU to a solution of R-3 in octane at room temperature

• with the synthesis of the starting materials and X. Lou for the help with the chiral HPLC measurements. This research was supported by a Small Scale Collaborative Project grant: Bottom-up Resolution of Functional Enantiomers from Self-Organised Monolayers (Project acronym: RESOLVE) seventh framework

Total synthesis of the indolizidine alkaloid tashiromine

• Stephen P. Marsden and
• Alison D. McElhinney

Beilstein J. Org. Chem. 2008, 4, No. 8, doi:10.1186/1860-5397-4-8

• with (−)-DIPCl according to Buynak et al. (Scheme 4) [41]. The desired hydroxysilane 12 was obtained in 53% yield and with 91% ee as determined by chiral HPLC analysis. Compound 12 was converted by standard methods to the acetate 14 and the tetrahydropyranyl ether 15. The latter compound was formed as

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• 13 : 1 by addition of 2,6-tert-butyl-4-methyl-pyridine as an acid scavenger (entry 4). Ultimately, we found that use of CH2Cl2 as the solvent and Et3N as base provided 3a in 78% yield with 20:1 trans/cis selectivity (entry 5). However, chiral HPLC analysis indicated that 3a from entry 5 had an