Lewis acid-promoted hydrofluorination of alkynyl sulfides to generate α-fluorovinyl thioethers

• Davide Bello and
• David O'Hagan

Beilstein J. Org. Chem. 2015, 11, 1902–1909, doi:10.3762/bjoc.11.205

• , giving the Z-stereoisomer 2c in 45% and 57% yields, respectively. We then maintained the phenyl moiety on the alkyne side of the sulfide, and replaced the benzyl group with a cyclohexyl fragment directly connected to the sulfur atom (compound 1d). This material allowed too for a stereoselective reaction

• , giving rise to the Z-stereoisomer of 2d in 47% and 68% yields, respectively. At this stage we decided to explore two simple variations of the groups directly connected to the ethynyl moiety, that are, a cyclopropyl group and the bulky tert-butyl group. Thus, we reacted cyclopropylethynyl(phenyl)sulfane

• completely stereoselective, furnished the Z-stereoisomer 2f in 40% and 62% yields, respectively, along with a 2% of difluorinated compound 4f. The formation of this byproduct could not be avoided; in fact lower temperatures or shorter reaction times did not change the outcome, and the contaminant 4f could

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

• allyl alcohol (4). The plausible mechanism of the formation of ROCM and ROMP products from exo- or endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles 1 or 2. For simplicity of the scheme, the reaction of only exo-stereoisomer 1 as a substrate is presented. Results of ROCM reactions of nitriles 1 and 2

Electrochemical oxidation of cholesterol

• Jacek W. Morzycki and
• Andrzej Sobkowiak

Beilstein J. Org. Chem. 2015, 11, 392–402, doi:10.3762/bjoc.11.45

• obtained in 32, 31, and 7% yields, respectively (Scheme 4). It is noteworthy that the reaction afforded a single stereoisomer of 11 or 12. Several important observations provided in the paper can give an idea on a plausible mechanism of cholesterol oxidation. First, in the absence of HMP and O2 only

Total synthesis of the proposed structure of astakolactin

• Takayuki Tonoi,
• Keisuke Mameda,
• Moe Fujishiro,
• Yutaka Yoshinaga and
• Isamu Shiina

Beilstein J. Org. Chem. 2014, 10, 2421–2427, doi:10.3762/bjoc.10.252

• stereoisomer (1’), with a Johnson–Claisen rearrangement, an asymmetric Mukaiyama aldol reaction, and our MNBA-mediated lactonization as key steps. It was found that the 1H and 13C NMR data of synthesized 1 and 1’ are not identical with those of the natural compound. Further studies to elucidate the complete

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

• spectrum there are 5 signals in the region from 108 to 40 ppm. The doublet at 108 ppm indicates the structure with sp2-hybridized carbon (CH(A)) and the triplet at 44 ppm indicates the existence of one geminal carbon atom. The tetracyclic oxazoline stereoisomer rel-(2S)-10 undergoes spontaneously oxazoline

Synthesis and bioactivity of analogues of the marine antibiotic tropodithietic acid

• Patrick Rabe,
• Tim A. Klapschinski,
• Nelson L. Brock,
• Christian A. Citron,
• Paul D’Alvise,
• Lone Gram and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2014, 10, 1796–1801, doi:10.3762/bjoc.10.188

• product was sufficiently pure for its direct usage in a Diels–Alder reaction with tetrachlorocyclopropene, resulting in the adduct 19 as a single stereoisomer. The formation of only one stereoisomer is explainable by an E/Z isomerisation of 18 and a Diels–Alder reaction that only proceeds from (Z)-18, but

Streptopyridines, volatile pyridine alkaloids produced by Streptomyces sp. FORM5

• Ulrike Groenhagen,
• Michael Maczka,
• Jeroen S. Dickschat and
• Stefan Schulz

Beilstein J. Org. Chem. 2014, 10, 1421–1432, doi:10.3762/bjoc.10.146

• the diastereomeric mixture of Wittig salts. Conclusively, 10 must be the last possible 1Z,3Z-stereoisomer. Both compounds 10 and 11 could not be isolated in pure form, but their mass spectra and retention times were identical to those of the natural products. The mass spectrum of compound 8 indicated

Synthesis of a sucrose dimer with enone tether; a study on its functionalization

• Zbigniew Pakulski,
• Norbert Gajda,
• Magdalena Jawiczuk,
• Jadwiga Frelek,
• Piotr Cmoch and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2014, 10, 1246–1254, doi:10.3762/bjoc.10.124

• of 10. Indeed, treatment of enone 10 with Zn(BH4)2 under the standard conditions afforded allylic alcohol 11 as single stereoisomer in 65% yield. Based on our model, the R-configuration might be safely assigned to the new stereogenic center. This assignment was further verified independently by

• circular dichroism spectroscopy (CD) using the in situ dimolybdenum methodology (see next chapter). Next steps of the synthesis consisted of the protection of the C6–OH as benzyl ether (to 12) and osmylation of the double bond. The cis-dihydroxylation provided, as single stereoisomer, a diol to which

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

• G. Gangadhararao,
• Ramesh Kotikalapudi,
• M. Nagarjuna Reddy and
• K. C. Kumara Swamy

Beilstein J. Org. Chem. 2014, 10, 996–1005, doi:10.3762/bjoc.10.99

• compound 7 was further confirmed by X-ray crystallography (Figure 2). The C=CHMe distance of 1.317(2) Å clearly indicates a double bond between these two carbon atoms. The other stereoisomer in which the methyl group is trans to the nitrogen was not observed. Interestingly though, the removal of the acyl

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

• -butyldimethylsilyl)]-β-cyclodextrin (50% in OV1701) as the stationary GC phase, operated at 100 °C. Under these conditions, the (2S,4S,6S)-enantiomer [30] is the later eluting stereoisomer, giving an α-value of (tr2:tr1) = 1.019 (see Supporting Information File 1, Figure S4). As a result of our investigations we

Synthesis of complex intermediates for the study of a dehydratase from borrelidin biosynthesis

• Frank Hahn,
• Nadine Kandziora,
• Steffen Friedrich and
• Peter F. Leadlay

Beilstein J. Org. Chem. 2014, 10, 634–640, doi:10.3762/bjoc.10.55

• -unsaturated aldehyde 11 in a pure form. Synthesis of DH substrate surrogate For the synthesis of the DH substrate surrogate 5a we aimed at an anti-selective aldol reaction, which permits efficient access to the desired 2D,3D-stereoisomer followed by a smooth transformation into the SNAc thioester in the

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• -stereoisomer (with respect to C-3 of the 1,2-oxazine ring) was isolated after column chromatography. A product derived from the minor isomer of nitrone 3 was not detected and was apparently lost during the reaction or the purification. Since the stereogenic center of the 1,3-dioxolane ring is converted into an

The regioselective synthesis of spirooxindolo pyrrolidines and pyrrolizidines via three-component reactions of acrylamides and aroylacrylic acids with isatins and α-amino acids

• Tatyana L. Pavlovskaya,
• Fedor G. Yaremenko,
• Victoria V. Lipson,
• Svetlana V. Shishkina,
• Oleg V. Shishkin,
• Vladimir I. Musatov and
• Alexander S. Karpenko

Beilstein J. Org. Chem. 2014, 10, 117–126, doi:10.3762/bjoc.10.8

• the most reactive sites of the reagents. The reaction proceeds regioselectively with the addition of the most nucleophilic methylene group carbon of the azomethine ylide to the most electrophilic sites of the acrylamide and benzoylacrylic acid, which affords only one stereoisomer of cycloadducts 4 and

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of ¹³C chemical shifts

• Simone Di Micco,
• Angela Zampella,
• Maria Valeria D’Auria,
• Carmen Festa,
• Simona De Marino,
• Raffaele Riccio,
• Craig P. Butts and
• Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

• coupling between vicinal protons H-15b–H-16 were chosen as the reference NOE for the 1D NOESY data set and the derived distance was adjusted for each stereoisomer in order to get the lowest MAE. To narrow the number of diastereoisomers, we initially analysed the relative configuration of C-7 and C-8, to

• polar and protic solvent such as methanol. Comparison of predicted 13C chemical shifts for 2a,b,e,f with the experimental values (Table 4) suggests the best fit with the experimental data for stereoisomer 2b. In particular, 2a presents a MAE more than twice the value found for 2b. The MAE of 2e is

• observed. The stereoisomer 2b shows all calculated 13C values falling in the proposed error limit of 2 ppm. For 2b, we observed a maximum error of 1.5 ppm. On the other hand, we found a |Δδ| of 2.5 ppm for 2f. Parallel with the MAE and |Δδ| analysis, we compared the calculated 13C chemical shifts with the

Total synthesis of the endogenous inflammation resolving lipid resolvin D2 using a common lynchpin

• John Li,
• May May Leong,
• Alastair Stewart and
• Mark A. Rizzacasa

Beilstein J. Org. Chem. 2013, 9, 2762–2766, doi:10.3762/bjoc.9.310

• stereoisomer analogues of RvD2 (1). Removal of the TIPS group with TBAF gave terminal alkyne 12. Alkyne 12 then underwent smooth hydrozirconation utilizing the procedure reported by Negishi [24] were ZrCp2HCl is generated in situ by reduction of ZrCp2Cl2 with DIBALH in THF. Iodinolysis of the zirconium species

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• , attempted separation by silica gel chromatography led to extensive decomposition. The product imine consisted of a single stereoisomer as determined by 19F NMR, tentatively assigned as the E-isomer. Similar to the formation of 1, it was easy to follow formation of the imine by 19F NMR with the resonance

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• detected, instead the syn-adduct 30 was obtained as the sole stereoisomer. By lowering the temperature to −40 °C and keeping the amount of reagents the same, the selectivity was inverted! Only the anti-adduct 29 was isolated. This change in selectivity was explained with two different transition states. At

New developments in gold-catalyzed manipulation of inactivated alkenes

• Michel Chiarucci and
• Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

• diastereoselection (i.e. cis stereoisomer as the major product) was recorded in the case of hydroxymethyl derivative 43. The challenging task of direct hydroamination with simple amines was faced, by means of in situ protection of the basic functionality as an ammonium salt (Scheme 12) [48]. The best catalyst for

Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes

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

Beilstein J. Org. Chem. 2013, 9, 2422–2433, doi:10.3762/bjoc.9.280

• is TS11exo (Figure 7), is in good agreement with the experimental results in which a high ee of the corresponding stereoisomer was observed. The formation of the enantiomer (TS11ent) was found to have an activation barrier of 4.5 kcal mol−1 higher in energy. That difference can be a consequence of

• compound 16 was identified (almost as unique diastereoisomer) in low chemical yield (<5%) together with two pyrrole derivatives 17 (only one stereoisomer), and 18. The last compound was formed by a retro-cycloaddition of the pyrroline 7aa with elimination of NMM, which was favoured by a prolonged heating

A concise enantioselective synthesis of the guaiane sesquiterpene (−)-oxyphyllol

• Martin Zahel and
• Peter Metz

Beilstein J. Org. Chem. 2013, 9, 2028–2032, doi:10.3762/bjoc.9.239

• completion of the synthesis of (−)-oxyphyllol (1) from 4. To our delight, a direct regio- and diastereoselective Co(II)-catalyzed hydration [12] of the olefin in 4 succeeded to give the required α-stereoisomer 3 in 58% isolated yield after chromatographic separation of the minor β-alcohol. Compared to the

An approach towards azafuranomycin analogs by gold-catalyzed cycloisomerization of allenes: synthesis of (αS,2R)-(2,5-dihydro-1H-pyrrol-2-yl)glycine

• Jörg Erdsack and
• Norbert Krause

Beilstein J. Org. Chem. 2013, 9, 1936–1942, doi:10.3762/bjoc.9.229

• . Fortunately, the correct stereoisomer was enriched at the stage of the dihydropyrrole 18 due to several purification steps. Desilylation of 15 with tetrabutylammonium fluoride trihydrate (94% yield) and conversion of 16 into the α-aminoallene 17 under Mitsunobu conditions (45% yield) [38][39][62] set the

Stereoselective synthesis of the C79–C97 fragment of symbiodinolide

• Hiroyoshi Takamura,
• Takayuki Fujiwara,
• Isao Kadota and
• Daisuke Uemura

Beilstein J. Org. Chem. 2013, 9, 1931–1935, doi:10.3762/bjoc.9.228

• protecting groups and subsequent stereoselective spiroacetalization were performed in one-pot with CSA in MeOH to provide spiroacetal 19 as a single stereoisomer [19][20]. The stereochemistry of 19 was elucidated by the observed NOE correlations between H-83 and H-91 as indicated by an arrow. The plausible

Diastereoselective radical addition to γ-alkyl-α-methylene-γ-butyrolactams and the synthesis of a chiral pyroglutamic acid derivative

• Tomoko Yajima,
• Eriko Yoshida and
• Masako Hamano

Beilstein J. Org. Chem. 2013, 9, 1432–1436, doi:10.3762/bjoc.9.161

• pyroglutamic acid derivative 13 as a single stereoisomer (Scheme 3). Conclusion In this study, we investigated the cis- and trans-stereoselective radical additions to α-methylene-γ-alkyl- γ-lactams. Strong cis-selectivities were observed using various γ-substituents under non-chelating conditions. The

Lanostane- and cycloartane-type triterpenoids from Abies balsamea oleoresin

• Serge Lavoie,
• Charles Gauthier,
• Jean Legault,
• Sylvain Mercier,
• Vakhtang Mshvildadze and
• André Pichette

Beilstein J. Org. Chem. 2013, 9, 1333–1339, doi:10.3762/bjoc.9.150

• ), 6 (δH 7.13) and 7 (δH 7.07), this suggested that the trans-stereoisomer was isolated instead of the cis-one (See Table 2 and Supporting Information File 1). This was further confirmed by NOESY correlation of H-24 to H-20 and H3-30, but not to H3-27. Consequently, the structure of 2 was determined as

Efficient regio- and stereoselective access to novel fluorinated β-aminocyclohexanecarboxylates

• Loránd Kiss,
• Melinda Nonn,
• Reijo Sillanpää,
• Santos Fustero and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2013, 9, 1164–1169, doi:10.3762/bjoc.9.130

• stereoisomer of 5 (Scheme 3, Figure 4). It is noteworthy that in this latter case hydroxylated amino ester 14 could not be prepared by the alternative diastereoselective epoxidation and regioselective oxirane opening strategy: according to our previous results, the opening of epoxide 15 derived from 10

• proceeded via a trans-diaxial chair conformation with the nucleophile attack on C4, thereby providing the 5-hydroxylated derivative [57][60]. Next, hydroxylated cyclohexane amino ester 14 was converted with Deoxo-Fluor in CH2Cl2 at 0 °C to 4-fluorinated ethyl β-aminocyclohexanecarboxylate 16, a stereoisomer

• -difluorinated cyclohexane amino ester 18, a stereoisomer of 9 (Scheme 4). Conclusion In conclusion, a simple and convenient procedure has been developed for the introduction of one or two fluorine atoms onto the skeleton of either cis- or trans-β-aminocyclohexanecarboxylates. The synthetic concept involves