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

A facile, rapid, one-pot regio/stereoselective synthesis of 2-iminothiazolidin-4-ones under solvent/scavenger-free conditions

• Murugan Sathishkumar,
• Sangaraiah Nagarajan,
• Poovan Shanmugavelan,
• Murugan Dinesh and
• Alagusundaram Ponnuswamy

Beilstein J. Org. Chem. 2013, 9, 689–697, doi:10.3762/bjoc.9.78

• obtained. Thus, the present investigation affording a single regioisomeric product exclusively is the first report wherein the allylic strains are noted to direct the high regioselectivity. Finally, the stereoselective formation of the (Z)-stereoisomer is also explicable based on allylic strain, which is

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• to 3.4:1 by replacement of the solvent (Table 1, entries 4 and 5). Thus, we developed an effective method for synthesis of the requisite stereoisomer 8 by applying a TBSOTf-promoted Diels–Alder reaction [25][26]. Most importantly, the C4-stereocenter behaved as the control element to introduce the

• afforded 22 as a single stereoisomer, and the obtained 22 was oxidized with DMDO to provide α-hydroxy aldehyde 23 as a diastereomeric mixture (dr = 2.8:1). Compound 23 then reacted with benzyl hydroxylamine to produce oxime 24, LiAlH4-treatment of which led to 25. The regioselective ring expansion of seven

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• replaced with various primary amines, one example being cyclopropylamine, which furnishes piperidine 129 as one stereoisomer. In the case of 1,2-diaminoethane, a further cyclisation is observed leading to bicyclic piperidine 130. All three components involved in this modular approach can be modified to

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• single stereoisomer was formed, with the H at the ring junction and the R group anti to each other. The stereochemistry of the cycloadducts was assigned by comparison with spectral data from previous work. This stereochemistry is consistent with that of previously reported intramolecular [4 + 2

trans-2-(2,5-Dimethoxy-4-iodophenyl)cyclopropylamine and trans-2-(2,5-dimethoxy-4-bromophenyl)cyclopropylamine as potent agonists for the 5-HT₂ receptor family

• Adam Pigott,
• Stewart Frescas,
• John D. McCorvy,
• Xi-Ping Huang,
• Bryan L. Roth and
• David E. Nichols

Beilstein J. Org. Chem. 2012, 8, 1705–1709, doi:10.3762/bjoc.8.194

• successful in leading to compounds with high affinity at the 5-HT2 family of receptors; and the more potent stereoisomer of the cyclopropane analogues had the expected (−)-(1R,2S)-configuration. Screening for affinity at various serotonin receptor subtypes, however, revealed that the cyclopropane congeners

• in leading to compounds with high affinity at the 5-HT2 family of receptors; and the more potent stereoisomer of the cyclopropane analogues had the expected (−)-1R,2S-configuration. However, at appropriate doses, although (−)-4 and (−)-5 may be useful as tools to probe 5-HT2 receptor function, one

The preferred conformation of erythro- and threo-1,2-difluorocyclododecanes

• Yi Wang,
• Peer Kirsch,
• Tomas Lebl,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2012, 8, 1271–1278, doi:10.3762/bjoc.8.143

• hyperconjugative interactions with the anti-periplanar C–H bonds, similar to that found in 1,2-difluoroethane in the well know gauche effect [10][11]. On the other hand, the erythro stereoisomer 5a would have a C–F bond projecting into the ring in an endo manner, if the vicinal fluorines were edge/edge located

• . The structures and relative energies for the erythro 5a and threo 5b isomers are shown in Figure 6. These data indicate that the corner/edge conformers are more stable than the alternative edge/edge conformers for each stereoisomer. This is consistent with the conclusions from the experimental VT 19F

• NMR study. For the erythro stereoisomer 5a, three conformers I–III were considered. Conformers I and II each have a fluorine pointing into the ring (endo), and thus there is an increase in transannular ring strain, raising the energy of these conformers by 2.81 and 3.72 kcal·mol−1 respectively above

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

• ]. Actually, 18 was first identified in the defensive secretions of dolichoderine ants [25]. The same substance (or its enantiomer) has been found as a defensive compound of Nematine larvae [30] and in adults and larvae of the thrips Calloccithrips fuscipennis [31]. A stereoisomer of dolichodial

• – anisomorphal (19) – is a component of the defensive secretion of the walking stick Anisomorpha buprestoides [32], whilst a third stereoisomer – peruphasmal (20) – has been identified in another walking stick, Peruphasma schultei [33][34]. Recent investigations show that the qualitative and quantitative

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

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• upon intramolecular aldol condensation [25][26][27]. Subsequently, the aldehyde 15 was reduced to the allylic alcohol 19 with LiAlH4 and converted into the acetate 20 [28]. Hydroboration of 20 using disiamylborane proceeded with high stereoselectivity affording 16 as a single stereoisomer [17][28

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step

• Dieter Enders,
• Jeanne Fronert,
• Tom Bisschops and
• Florian Boeck

Beilstein J. Org. Chem. 2012, 8, 1112–1117, doi:10.3762/bjoc.8.123

• ), the (S)-proline catalyzed 5-enolexo aldol key step of this synthesis could be performed in good yield (71%). To our delight, we found in this case an exceedingly high diastereo- (99%) and enantioselectivity (99%) for the aldol reaction, furnishing the aldol product 14 as a single stereoisomer. The

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

• define a specific orientation or conformation of each stereoisomer (trans or cis). Recently, Carreño et al. [132][133] synthesized different enantiomerically pure sulfinyl azobenzenes. The sulfinyl group is a key component in the design of a molecular sunflower, a device that by means of light can

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

• Zakir Hussain,
• Henning Hopf,
• Khurshid Ayub and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

• compound(s) was found to give a mixture of stereoisomers. However, in the present case, we were only able to isolate 4 as a single stereoisomer. Furthermore, the procedure for the synthesis of compounds 4 and 5 is essentially the same as described previously for analogous compounds [10]. The complete

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

• Yoshihiro Nishida,
• Yuko Shingu,
• Yuan Mengfei,
• Kazuo Fukuda,
• Hirofumi Dohi,
• Sachie Matsuda and
• Kazuhiro Matsuda

Beilstein J. Org. Chem. 2012, 8, 629–639, doi:10.3762/bjoc.8.70

• conformation. Here, it should be mentioned that the conformer distribution coincides between I-a (Figure 3, entry 5) and DPPC (Figure 3, entry 2) at the head moiety [gt (33%), gg (34%) and tg (33%)]. The above analysis was carried out also for the stereoisomer I-b and the related glycolipids (Figure 4, entries

• conformer in I-b is reversed (anticlockwise) from the case of DPPC and GGPL-I (clockwise), as depicted in Figure 3 and Figure 4. Conclusion We have proposed a synthetic pathway to a GGPL-I homologue and its stereoisomer, in which our one-pot α-glycosylation methodology was effectively applied. We envisage

Conserved and species-specific oxylipin pathways in the wound-activated chemical defense of the noninvasive red alga Gracilaria chilensis and the invasive Gracilaria vermiculophylla

• Martin Rempt,
• Florian Weinberger,
• Katharina Grosser and
• Georg Pohnert

Beilstein J. Org. Chem. 2012, 8, 283–289, doi:10.3762/bjoc.8.30

• not be resolved due to the substantial overlap of the signals. An isomer of 5 bearing also a conjugated tetraene unit was isolated and tentatively assigned to a stereoisomer with an E-configured double bond between C11 and C12 and open stereochemistry of the C7/C8 bond. Despite the stereocenter at C4

Synthesis of fused tricyclic amines unsubstituted at the ring-junction positions by a cascade condensation, cyclization, cycloaddition then decarbonylation strategy

• Iain Coldham,
• Adam J. M. Burrell,
• Hélène D. S. Guerrand,
• Luke Watson,
• Nathaniel G. Martin and
• Niall Oram

Beilstein J. Org. Chem. 2012, 8, 107–111, doi:10.3762/bjoc.8.11

• alkene. A single stereoisomer of product 2 was formed. Alternatively, glycine could be used and led to a tricyclic product via an intermediate azomethine ylide formed by decarboxylation. Unfortunately, when the substrate 1 (R = H) was used, heating with glycine or glycine ethyl ester did not yield the

• glycine ethyl ester in toluene gave the desired tricyclic product 13a as the major stereoisomer, together with a small amount of the separable stereosiomer 13b (Scheme 4). The major isomer 13a was assumed to have the all-cis configuration based on related chemistry (compare with product 2 [19][20], Scheme

• glycine in toluene gave the desired tricyclic product 19 as a single stereoisomer. NOESY studies verified the stereochemistry as shown. Only one of the two alkene groups acts as the dienophile, as expected for conformational reasons. This synthesis (six steps from nitrile 3) represents an efficient entry