Self-assembly of metallosupramolecular rhombi from chiral concave 9,9’-spirobifluorene-derived bis(pyridine) ligands

• Rainer Hovorka,
• Sophie Hytteballe,
• Torsten Piehler,
• Georg Meyer-Eppler,
• Filip Topić,
• Kari Rissanen,
• Marianne Engeser and
• Arne Lützen

Beilstein J. Org. Chem. 2014, 10, 432–441, doi:10.3762/bjoc.10.40

• the conclusions drawn from the 1H NMR spectra. Two individual peaks for the two diastereomers can be detected when (rac)-3 is employed for complexation and the intensities of the signals of the racemic homochiral diastereomer are approximately three times as large as those of the signals of the

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines – development of a phosphite-driven cyclodehydration

• Peter H. Huy,
• Julia C. Westphal and
• Ari M. P. Koskinen

Beilstein J. Org. Chem. 2014, 10, 369–383, doi:10.3762/bjoc.10.35

• a single diastereomer according to 1H NMR. Importantly for up-scaling, only a slight excess of L-Selectride (1.3 equiv) or Superhydride (1.5 equiv), respectively, was required for the quantitative conversion of 7a–d to the intermediate II. Therefore the deprotonation of the free OH-group of 7 must

• starting material 14a was dissolved in the less polar CH2Cl2 (rather than THF), the dr further increased to >19:1 (entry 6). Moreover, N-Selectride provided the product 9a almost as a pure diastereomer (entry 7, solvent THF), only a very small trace of the syn-diastereomer was visible in the 1H NMR (400

• temperature, immediate L-Selectride reduction (giving intermediate V), HCl quenching and Et3N-induced cyclisation afforded the piperidine trans-11a in an excellent ee (≥99%) and as a single diastereomer according to crude 1H NMR. Although the reduction is performed in the presence of a secondary amino

Decandrinin, an unprecedented C₉-spiro-fused 7,8-seco-ent-abietane from the Godavari mangrove Ceriops decandra

• Hui Wang,
• Min-Yi Li,
• Félix Zongwe Katele,
• Tirumani Satyanandamurty,
• Jun Wu and
• Gerhard Bringmann

Beilstein J. Org. Chem. 2014, 10, 276–281, doi:10.3762/bjoc.10.23

• shown in Figure 4. A plausible biogenetic precursor of decandrinin (1) might be the naturally more common β-diastereomer of 7,13-ent-abietadien-3-ol (2). Accordingly, its 3β-OH group would be oxidized to yield int A, whose C-9 would then be hydroxylated to afford int B. Oxidative cleavage at the ∆7,8

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

• -component adducts were isolated in good yields up to 92%. A single diastereomer was detected with maleimides; the diastereoselectivity being lower with methyl acrylate and vinyl oxazolidinone (Scheme 7). A one-pot, palladium-mediated cycloisomerization of ene-ynes 5 was applied to the synthesis of 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

• single diastereomer) which may be due to the stabilized carbenium ion formed at the benzylic position. This rearrangement presents a relatively rare example of an intramolecular aldol-like reaction of an enol ether with an activated acetal (which may also be regarded as a special case of a Prins reaction

• . For this reason, it is assumed that the 2-H proton of 13 is cis-orientated to the 1-H and 4-H protons and consequently shows an (R)-configuration. Ketones 11, 12 and 13 were subsequently smoothly reduced with sodium borohydride in ethanol. In all cases, only one diastereomer (hydroxy group at C-10

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• equatorial attack in the rearrangement of cyclohexenyl acetates and observed a strong preference for the stereochemically controlled axial approach. The size of the protecting groups had a strong influence on the face-selectivity, furnishing in case of the TBS derivative only one diastereomer. By

• AIBN gave the desired α-allylated product 61. We used the high substrate control to construct the first quaternary center at C13 by trapping the potassium enolate of 61 with MeI, furnishing the desired product as a single diastereomer. Isomerization of the terminal double bond with cat. PdCl2(CH3CN)2

• tetraallyltin and BuLi affording a 2:1 mixture of diastereomers, with the desired diastereomer being the minor product. The stereochemistry was unambiguously confirmed by crystal structure analysis of a derivative of the major diastereomer [36]. Thus, the preference for the axial attack predominates the aimed

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

• established that (+)-5-hydroxydendrolasin (7) has an R configuration. Likewise, the 1H NMR spectrum of the MPA ester of (−)-7b was identical to that of the synthetic diastereomer (R,S)-11. Taking into account the change in sign of [α]D between the alcohol and its acetate derivative, these data verified that

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

• ]. Structural characterization of SF5-containing β-lactams Isolated as a single diastereomer, the relative stereochemistry of 7a, the product of the Staudinger reaction of 5a, is shown in Figure 1. The cis relative stereochemistry of β-lactam is consistent with 1,2-lk conrotatory ring closure of the E-imine 5a

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

• and 50 mol % of ZnBr2 was added, the reaction gave the anti-adduct 49 as the major diastereomer (12:1 anti/syn). When the amount of ZnBr2 was lowered to half (25 mol %) the selectivity rose to 20:1 (anti/syn). The selectivity was reversed to 1:15 (anti/syn) favouring the syn-adduct 16, when the

The total synthesis of D-chalcose and its C-3 epimer

• Jun Sun,
• Song Fan,
• Zhan Wang,
• Guoning Zhang,
• Kai Bao and
• Weige Zhang

Beilstein J. Org. Chem. 2013, 9, 2620–2624, doi:10.3762/bjoc.9.296

• mixture of diastereomers [19]. This mixture was separated using silica gel chromatography to achieve a 78% overall yield over three steps. The unwanted syn-diastereomer 4' was converted into the required anti-diastereomer 4 via Mitsunobu inversion followed by removal of the benzoate group under basic

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C₃-building block

• Volker M. Schmiedel,
• Stefano Stefani and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2013, 9, 2564–2569, doi:10.3762/bjoc.9.291

• diastereomer were obtained in five steps with a good overall yield of 42% with respect to aldehyde 6. This result was very encouraging and we therefore started the preparation of the enantiopure natural product and its stereoisomers. Synthesis of enantiopure jaspine B using a carbohydrate-derived alkoxyallene

• jaspine B (1) and its (2S,3R,4R)-diastereomer 2 in 91% yield. Unfortunately, none of the diastereomeric mixtures obtained in all steps depicted in Scheme 6 were easily separable by HPLC, either due to the instability of the obtained compounds or the similar Rf values of the tetrahydrofuranol pairs 9/10

• to an enhanced difference of dipole moments and hence Rf values of the two isomers (Scheme 7). Final hydrogenolysis of the separated diastereomers 16 and 17 led to deprotection of the hydroxy group and simultaneous reduction of the azido group. Jaspine B (1) and its (2S,3R,4R)-diastereomer 2 were

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A

• Jie Zhang,
• Hong-Kui Zhang and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2013, 9, 2358–2366, doi:10.3762/bjoc.9.271

• of (R)-3-(tert-butyldimethylsilyloxy)glutarimide 14. After O-desilylation and Dess–Martin oxidation, the resulting keto-lactam 10 was subjected to a highly trans-stereoselective addition of the methylmagnesium iodide to give carbinol 11 as sole diastereomer. An efficient ring closure procedure

• as an advanced intermediate for the synthesis of pumiliotoxin 251D [12]. Later on, Nubbemeyer and co-workers used the Horner olefination to convert 5 and its diastereomer into (+)-PTX 251D (2) and the 8-epimer of PTX 209F (4), respectively [17]. Recently, (8S,8aS)-5 has been used for the synthesis of

• minor diastereomer. Similar results have been reported by Nubbemeyer [27] and Li [8]. In view of the fruitless efforts of Nubbemeyer [27] and Li [8] in inversing the diastereoselectivity of the methylation reaction of keto-lactam 7, an alternative approach was envisaged. To develop a diastereoselective

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

• Peter A. Wade,
• Alma Pipic,
• Matthias Zeller and
• Panagiota Tsetsakos

Beilstein J. Org. Chem. 2013, 9, 2137–2146, doi:10.3762/bjoc.9.251

• in 10% yield was a competing reaction in toluene: further studies with additional substrates may lead to a useful new 3-component synthesis of nitro compounds, especially considering the observation that only one diastereomer (mixture of o,p-isomers) was observed. Interestingly, reaction with (Z)-3

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

• Thomas C. Nugent,
• Richard Vaughan Williams,
• Andrei Dragan,
• Alejandro Alvarado Méndez and
• Andrei V. Iosub

Beilstein J. Org. Chem. 2013, 9, 2103–2112, doi:10.3762/bjoc.9.247

• drs (Table 2). Based on these Pt, Pd, and Ni results two important conclusions were arrived at: i) on average, when using an active-surface catalyst such as Pd/C or Pt/C, the trans-imine provides the major diastereomer, (S,S)-3, while the cis-imine the minor diastereomer (S,R)-3 (Scheme 1). Hence, the

• relationship between imine cis/trans ratios and their reduction product (chiral amine) diastereomer ratios. Density functional theory modeling of the experimentally explored imines discussed in this paper did not support the alternative hypothesis that we set out to consider, namely that the carbonyl

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• diazolactams 43a/b was developed. The necessary cycloglycosidative coupling of 45 and (+)-41 was promoted by camphorsulfonic acid to give the DMB-protected K252a [(−)-46] as a 2:1 mixture, slightly favoring the desired diastereomer. Cleavage of the N-protecting group gave (−)-K252a [(−)-27] as its unnatural

• provided the depicted endo-diastereomer in good yield. Exchange of the N-benzyl for a Boc-protecting group and cleavage of the silyl enol ether gave the corresponding ketone, which was first converted to an enol-triflate and then to the tricyclic alkene 73. At this stage, the syntheses of cytochalasin B

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

• stage for the gold-catalyzed cycloisomerization. This was carried out with 10 mol % each of AuCl and imidazole in toluene at 100 °C to give the desired dihydropyrrole 18 in ca. 67% yield. Similar to the diastereomer 10b, compound 18 could not be purified in a sufficient manner even after repeated column

• )}. For the debromination of dihydropyrrole 19, we first tested radical conditions ((n-Bu)3SnH/AIBN), but these led to complete decomposition. This is surprising since carbamates are known to be stable under radical conditions [70]. Indeed, treatment of diastereomer 11b with (n-Bu)3SnH/AIBN afforded 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

• to the Sharpless AD [15] with AD-mix-β to furnish the C79–C97 fragment 27 in 72% yield as a single diastereomer (Scheme 5). The configuration of the resulting two vicinal hydroxy groups at C93 and C94 of 27 were unambiguously confirmed by the modified Mosher method, respectively (see Supporting

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• a small amount of THF to dissolve the starting material). The oxy-Michael addition with chiral thiourea and phenylboronic acid proceeded to give a single diastereomer; however, after 48 h at 50 °C, only 17% of the syn diol was formed, and 56% of the starting material was re-isolated. Under the

• acetonide diastereomer. In the course of investigating why 66 and 67 failed to react, attempts were made to trap the anion of 67 with a more reactive electrophile. Allyl bromide reacted rapidly, affording the product 73 as a single diastereomer (Scheme 19). The configuration of this compound, as well as

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

• as a single diastereomer [11][12] (Scheme 2). Hydrolysis with CF3CO2H and converting the hydroxy group to the chloride yielded the corresponding lactam 9 [13]. The chiral auxiliary was removed by DBU-assisted elimination to the enamine and subsequent hydrolysis [14]. Introducing the pivaloyl group

α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

• Åsmund Kaupang and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2013, 9, 1407–1413, doi:10.3762/bjoc.9.157

• N-methylene groups of the amide [44]. With the exception of the piperazine derivative 5d, the observed diastereomeric ratio in the β-lactam products was approximately 6:1, favouring the diastereomer in which the bromine atom and the ring fragment are in a trans relationship (hereafter referred to as

Catalytic asymmetric tandem Friedel–Crafts alkylation/Michael addition reaction for the synthesis of highly functionalized chromans

• Jiahuan Peng and
• Da-Ming Du

Beilstein J. Org. Chem. 2013, 9, 1210–1216, doi:10.3762/bjoc.9.137

• , entries 3–5), the reaction gave the opposite stereoselectivities probably because of the lower steric hindrance compared with I and II. Although the opposite diastereomer was obtained in good yield and stereoselectivity with the use of ligand IV, ligand I was the preferred one according to the results. In

• decreased significantly (Table 4, entry 11). The configuration of the major diastereomer of 3g was determined to be C15(S), C16(R), C17(S) (Figure 2), and those of other products were assigned by analogy [51]. The results of the substrate scope are unsatisfactory. The yields of the desired products 3 were

• was stirred for another 24 h at room temperature. The solvent was removed under vacuum. Purification by column chromatography afforded the desired products 3. Diphenylamine-linked bis(oxazoline). X-ray crystal structure of the major diastereomer of 3g (one symmetric molecule and two solvent molecules

The conjugation of nonsteroidal anti-inflammatory drugs (NSAID) to small peptides for generating multifunctional supramolecular nanofibers/hydrogels

• Jiayang Li,
• Yi Kuang,
• Junfeng Shi,
• Yuan Gao,
• Jie Zhou and
• Bing Xu

Beilstein J. Org. Chem. 2013, 9, 908–917, doi:10.3762/bjoc.9.104

• diastereomer of 1a, hydrogelator 1b exhibits quite different behavior in terms of self-assembly and hydrogelation. For example, at a concentration of 0.8 wt %, 1b forms a solution at pH 9.0 and 60 °C, and the solution remains after the conditions have been adjusted to pH 7.0 and room temperature. Further

Synthesis of skeletally diverse alkaloid-like molecules: exploitation of metathesis substrates assembled from triplets of building blocks

• Sushil K. Maurya,
• Mark Dow,
• Stuart Warriner and
• Adam Nelson

Beilstein J. Org. Chem. 2013, 9, 775–785, doi:10.3762/bjoc.9.88

• diastereoiomers; following column chromatography, the major diastereomer 22 was obtained in 70% yield, and was converted into the corresponding amino alcohol 23. The configuration of the amino alcohol 23 was determined by conversion into the corresponding benzamide and comparison with racemic and enantiomerically

Carbolithiation of N-alkenyl ureas and N-alkenyl carbamates

• Julien Lefranc,
• Alberto Minassi and
• Jonathan Clayden

Beilstein J. Org. Chem. 2013, 9, 628–632, doi:10.3762/bjoc.9.70

• -coordinating solvent suppresses rearrangement of the product [4]) at −40 °C: it underwent clean carbolithiation of the double bond, and on protonation urea 4a was obtained as a single diastereomer in 85% yield (Scheme 2 and Table 2, entry 1). Other E-alkenyl ureas bearing a range of substituted aromatic rings

• E-3b–f were likewise treated with alkyllithium reagents s-BuLi, iPrLi and t-BuLi, this time in toluene. As before, a noncoordinating solvent was used to suppress rearrangement. In each case the addition product 4b–f was obtained in good yield always as a single diastereomer (Table 2, entries 2–5 and

• materials, Z-3e and Z-3f (Scheme 2 and Table 2, entries 6 and 8), the other diastereomer of the product urea epi-4 was obtained selectively: the carbolithiation–protonation is completely diastereospecific. Both geometrical isomers of 3 presented similar reactivity and the products 4 were obtained in similar

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

• potent steroid contraceptive desogestrel (79), as outlined in Scheme 16 [36]. Thus, radical addition to alkene 76 furnishes intermediate 77, after deprotection of the second ketone group. Exposure of the latter compound to base results in the formation of bicycle 78 as one diastereomer. While the