Selective bromochlorination of a homoallylic alcohol for the total synthesis of (−)-anverene

• Frederick J. Seidl and
• Noah Z. Burns

Beilstein J. Org. Chem. 2016, 12, 1361–1365, doi:10.3762/bjoc.12.129

• reduced with dimethyl phosphonate [16][17]. While the mechanism of this Hirao reduction is not fully understood, the reaction was exquisitely mild and proceeded with high chemoselectivity for the geminal dihalide, delivering (−)-anverene (1) in high yield as a 7:1 mixture of E/Z isomers. Following

On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• ]. Formation of the imine E-7 and Cr(CO)6 from the carbene complex Cr(CO)5(Z-6) requires heating to 170 °C for 3 days under CO pressure (Scheme 1c) [42]. At room temperature and in the presence of base (KOt-Bu), M(CO)5(Z-8) (M = Cr, W) simply isomerize to a mixture of E/Z isomers M(CO)5(E-8)/M(CO)5(Z-8

A robust synthesis of 7,8-didemethyl-8-hydroxy-5-deazariboflavin

• Matthias Bender,
• Henrik Mouritsen and
• Jens Christoffers

Beilstein J. Org. Chem. 2016, 12, 912–917, doi:10.3762/bjoc.12.89

• , 4.00 mmol, 87%; mixture of E/Z isomers, ratio ca. 3:1), which was submitted to reduction without further purification. HRMS (ESI+): calcd for C11H19NNaO5 268.1161, found 268.1157 [M + Na]+. Reduction to the amine 10: A solution of the above reported oxime (985 mg, 4.00 mmol) in abs. THF (anhydrous, 20

Study on the synthesis of the cyclopenta[f]indole core of raputindole A

• Nils Marsch,
• Mario Kock and
• Thomas Lindel

Beilstein J. Org. Chem. 2016, 12, 334–342, doi:10.3762/bjoc.12.36

• presence of Boc-protected indole nitrogens an acid-catalyzed Meyer–Schuster rearrangement was dismissed. Instead, a transition metal-catalyzed rearrangement employing 1 mol % of MoO2(acac)2/[Au(PPh3)Cl]/AgOTf [37] afforded the α,β-unsaturated ketone 8 as a 2:1 mixture of E/Z isomers (86%), which could not

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• of E/Z isomers) [25], the identification of all ROCM components of the aforementioned mixtures was performed. The results of these experiments are given in Table 1 and Table 2. The collected data show that the reactions in diluted solutions (Table 1, entries 1, 7, 10, and 13) led mainly to ROMP

• , namely Grubbs II and Hoveyda–Grubbs II, favored the formation of ROMP products. A different distribution of E/Z-isomers was observed in the reaction of substrate 1 with alcohol 3 in the presence of the Steward–Grubbs ([Ru]5) catalyst (Table 2, entry 5). The E-isomers of both products 5 and 6 prevailed

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• reacted with azetidine-2,3-diones 176 under eco-friendly reaction conditions to generate bis(allene) 177. Compound 177 was then converted into bis(dihydrofuran) 178 by using AuCl3. Macrocyclization of 178 was carried out by using a Ru(II) or Ru(III) catalyst to generate 179 as a mixture of E/Z isomers

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

• , reaction of ketone 127 with the lithium anion of sulfone 128 and treatment of the obtained β-hydroxysulfone with SmI2 led to olefin 129 as a 2:1 mixture of E/Z-isomers. After reduction of the tert-butyl ester to the primary alcohol, the E/Z-isomers could be separated chromatographically. Cleavage of the

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• -ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single

• fast so that a separation of a pure sample failed. The iodo derivative 13e gave low yields and despite of intense efforts we were not able to obtain the compounds in pure form. Solutions of pure samples of the E/Z-isomers 13a–d and 14a,c,d, respectively, equilibrated slowly in chloroform solutions to

Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)

• Armin Tröger,
• Teris A. van Beek,
• Martinus E. Huigens,
• Isabel M. M. S. Silva,
• Maarten A. Posthumus and
• Wittko Francke

Beilstein J. Org. Chem. 2014, 10, 767–773, doi:10.3762/bjoc.10.72

• of 8 showed an E/Z-ratio of ca. 2:1 and was highly dominated by the anti-isomers (see Supporting Information File 1, Figure S1). The E/Z-isomers of the two pairs of diastereomers could be separated by gas chromatography. Analysis by coupled gas chromatography/mass spectrometry (GC–MS) showed the 70

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

• experimental aspects [49]. When the dechlorination was carried out in the presence of an aldehyde, the dimer was immediately converted to the expected corresponding homoallylic alcohols 14 in moderate to good yields as mixtures of E/Z isomers (Scheme 12). In 2005, Welker and co-workers started a series of

Synthesis and determination of the absolute configuration of (−)-(5R,6Z)-dendrolasin-5-acetate from the nudibranch Hypselodoris jacksoni

• I. Wayan Mudianta,
• Victoria L. Challinor,
• Anne E. Winters,
• Karen L. Cheney,
• James J. De Voss and
• Mary J. Garson

Beilstein J. Org. Chem. 2013, 9, 2925–2933, doi:10.3762/bjoc.9.329

• obtained by preparative enantioselective HPLC. Keywords: enantioselective HPLC; E/Z-isomers; Hypselodoris; natural products; nudibranch; sesquiterpene; Introduction Marine organisms have been proven a prolific source of natural products that potentially can be used as lead compounds or which have

• individual stereoisomers (see below). The 3:1 ratio of E/Z-isomers was confirmed via analytical HPLC. In principle, the rearrangement of 6 could afford either [1,2]-rearranged products (e.g. 7a/b or 8) or [2,3]-rearranged products such as 9 or 10 depending on which site adjacent to the ether oxygen is

• , although such data must be interpreted with care. With the individual characterization of the E/Z-isomers accomplished, preparative enantioselective HPLC separation of racemic (Z)-5-hydroxydendrolasin (7b) was next undertaken (Figure 4) and provided samples of both of the (+)-7b and (−)-7b isomers

Homolytic substitution at phosphorus for C–P bond formation in organic synthesis

• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 1269–1277, doi:10.3762/bjoc.9.143

• photoinduced addition of tetrafluorodiphosphine to alkenes and alkynes in the gas phase (Table 3) [31][32][33][34]. The addition provides a series of intriguing bidentate phosphine ligands. The addition to alkynes yields 1:1 mixtures of E/Z isomers. Due to the high reactivity of a difluorophosphanyl radical

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• their photochromic azo units have been equilibrated in the photostationary state. The composition of the photostationary state was investigated for compounds 15 and 2 by NMR spectroscopy. In the case of 15 the ratio of the E/Z isomers is 1/1.2 in the photostationary state corresponding to a degree of

A new phenylethyl alkyl amide from the Ambrostoma quadriimpressum Motschulsky

• Guolei Zhao,
• Chao Yang,
• Bing Li and
• Wujiong Xia

Beilstein J. Org. Chem. 2011, 7, 1342–1346, doi:10.3762/bjoc.7.158

• according to the synthetic plan shown in Scheme 5. Oxidation of the alcohol 12 with PCC afforded the corresponding aldehyde 16, followed by a Wittig reaction with salt 15 in the presence of two equiv LDA, which afforded the adduct 17 as an (E/Z)-mixture in 72% yield. The E/Z isomers of 17 were not separated

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

• , and thus proximity-facilitated tandem hydride transfer/cyclization sequence [33]. Since the yields of rac-15 from the alkene rac-13 were low, we turned our attention to an alternative approach via the enol ether 18, which was available from 9 as a 1:1 mixture of E/Z-isomers by Wittig reaction with

• , for example with MeO2CCH=PPh3 or MeO2CCH2P(O)(OEt)2/n-BuLi, failed. By contrast, Peterson-type olefination using TMSCH2CO2Et/LDA cleanly afforded the α,β-unsaturated ester 20 as a 77:23 mixture of the E/Z-isomers in 50% yield. The reduction of the conjugated double bond with Mg in methanol furnished