Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• nitroalkenes in the presence of Ni(II) complexes with various chiral vicinal diamines was studied. This reaction provides convenient access to non-racemic 4-nitro-2-sulfonylbutan-1-ones with two stereocenters with high yield and excellent enantioselectivity (up to 99%). It has been established that the

• acids are attached to 1,2-disubstituted α,β-unsaturated sulfones in the presence of the Rh/(S,S)-chiraphos catalytic system. Modern methods for the synthesis of functionalized sulfones, with stereocenters in the side chain, by Michael addition are based, mainly, on the use of vinyl sulfones as Michael

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• afford polysubstituted cyclopropanols (or cyclopropylamines) potentially bearing several diastereo- and enantiomerically enriched adjacent stereogenic centers, including quaternary carbon stereocenters, as single diastereo- and enantiomer from a simple precursor, it would certainly provide an additional

• the oxidation of the cyclopropylcopper species proceeded equally well and gave the corresponding cyclopropanols possessing two adjacent quaternary carbon stereocenters (7i–r) in good yields and excellent diastereomeric ratios. Here again, the methyl, the alkyl group from the organometallic and the

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• by many different routes, controlling the configuration of the exocyclic olefin as well as that of stereocenters on and adjacent to the three-membered ring remains a challenging task [15]. In this context, cyclopropenes can serve as useful precursors of substituted and functionalized

• to access functionalized alkylidenecyclopropanes, with creation of a new carbon–carbon bond on the three-membered ring with the control of two contiguous stereocenters. Ireland–Claisen rearrangement of cyclopropenylcarbinyl esters The Ireland–Claisen rearrangement of silyl ketene acetals generated

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• N-Boc-isatin imines 3 with silyl ketene imines 27 catalyzed using a combination of Zn(OTf)2 and chiral N,N’-dioxide ligand 28 [48]. As shown in Scheme 9, this remarkable process afforded a wide range of chiral β-amino nitriles 29 exhibiting two vicinal tetrasubstituted stereocenters as almost single

A stereoselective and flexible synthesis to access both enantiomers of N-acetylgalactosamine and peracetylated N-acetylidosamine

• Bettina Riedl and
• Walther Schmid

Beilstein J. Org. Chem. 2018, 14, 856–860, doi:10.3762/bjoc.14.71

• configuration at C4 and C5 of the target compounds 5a and 5b. After the C4-chain of tartaric acid has been extended by two carbon atoms resulting in compounds 4a and 4b, two new stereocenters have been introduced by Sharpless epoxidation [17][18]. We applied this approach for the epoxidation of 4a with L

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• stereocenters were formed giving either the syn-2 or the anti-isomers 3. In all reactions one of the diastereomers was formed in large excess. In most cases, this isomer was isolated in an almost pure form after repeated chromatography, which explains the low isolated yields. Unfortunately, all products are

• oils and could not be crystallized. Thus, in order to determine the relative stereochemistry, we analyzed the vicinal coupling constants of the protons attached to the stereocenters. In the syn-isomers 2 these protons are anti to each other, while in the anti-isomers 3 these protons are in a syn

Stereochemical outcomes of C–F activation reactions of benzyl fluoride

• Neil S. Keddie,
• Pier Alexandre Champagne,
• Justine Desroches,
• Jean-François Paquin and
• David O'Hagan

Beilstein J. Org. Chem. 2018, 14, 106–113, doi:10.3762/bjoc.14.6

• bimolecular SN2 substitution would result in a complete inversion of configuration of the stereocenter and perfect enantiospecificity, while an SN1 mechanism would yield a fully racemized product. Any mixed pathway would generate products with partially racemized stereocenters. In this context, we decided to

A Brønsted base-promoted diastereoselective dimerization of azlactones

• Danielle L. J. Pinheiro,
• Gabriel M. F. Batista,
• Pedro P. de Castro,
• Leonã S. Flores,
• Gustavo F. S. Andrade and
• Giovanni W. Amarante

Beilstein J. Org. Chem. 2017, 13, 2663–2670, doi:10.3762/bjoc.13.264

• significant anti-angiogenesis activity [31]. It is worth mentioning that this product has three consecutive stereocenters and different sites of variation from the original natural product. The hydride comes from the less hindered side of the ketone moiety, leading to the formation of a hydroxy group in cis

Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity

• Tathagata Mukherjee,
• Soumik Biswas,
• Andreas Ehnbom,
• Subrata K. Ghosh,
• Ibrahim El-Zoghbi,
• Nattamai Bhuvanesh,
• Hassan S. Bazzi and
• John A. Gladysz

Beilstein J. Org. Chem. 2017, 13, 2486–2501, doi:10.3762/bjoc.13.246

• cases, CF2CF2OCF(CF3)CF2OCF(CF3)- segments have been found to impart higher fluorophilicites than similar perfluoroalkyl groups [42]. However, the multiple CF(CF3) stereocenters are disadvantageous, as they render such compounds mixtures of diastereomers, presenting an impediment to crystallization. In

A permutation approach to the assignment of the configuration to diastereomeric tetrads by comparison of experimental and ab initio calculated differences in NMR data

• Przemysław J. Boratyński

Beilstein J. Org. Chem. 2017, 13, 2478–2485, doi:10.3762/bjoc.13.245

• . Keywords: GIAO; NMR; stereochemistry assignment; Introduction In a stereodivergent synthesis [1] often two or more new stereocenters are created with or without control of stereochemistry and it is necessary to identify the configuration of the products. Any diastereomers exhibit disparate NMR spectra

• encompass all stereomers at two selected stereocenters. Thus all possible configurations, e.g., RR, RS, SR, and SS need to be distributed to four isomeric compounds. For four different items there are overall P4 = 4! = 24 possible permutations. In other words, there are 24 ways in which configurations could

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

• reduction with DIBAL-H [125]. Aldehyde (R)-17 was submitted to an asymmetric Brown crotylation reaction [126][127] to establish the C16 and C17 stereocenters. Of note, all four possible C16,C17-diastereomers of 18 were prepared (not shown) by using different combinations of (E)- or (Z)-butene and either

• moiety. The synthesis of alkyl iodide 23 departed from TBS-protected 5-hydroxypentanal 22 and proceeded via an asymmetric Brown crotylation to establish the C5 and C6 stereocenters. Intermediates 21 and 23 were combined under Smith’s modified [134] Negishi cross-coupling [124] conditions to furnish the

A speedy route to sterically encumbered, benzene-fused derivatives of privileged, naturally occurring hexahydropyrrolo[1,2-b]isoquinoline

• Olga Bakulina,
• Alexander Ivanov,
• Vitalii Suslonov,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2017, 13, 1413–1424, doi:10.3762/bjoc.13.138

• -diastereoselectivity of the CCR is well documented in the literature [33] and is, therefore, unsurprising. However, the stereocontrol achieved in this reaction over 3 stereocenters present in 10l (obtained in 81% yield as a single diastereomer) is certainly quite noteworthy and was confirmed by X-ray analysis (Figure

Synthesis of the heterocyclic core of the D-series GE2270

• Christophe Berini,
• Thibaut Martin,
• Pierrik Lassalas,
• Francis Marsais,
• Christine Baudequin and
• Christophe Hoarau

Beilstein J. Org. Chem. 2017, 13, 1407–1412, doi:10.3762/bjoc.13.137

• side-hydrolysis of sensitive functions, as well as epimerization of stereocenters [25]. The first condensation step leading to the thiazoline intermediate was successfully achieved, although in the presence of molecular sieves without KHCO3. The latter was then immediately dehydrated at low temperature

Construction of highly enantioenriched spirocyclopentaneoxindoles containing four consecutive stereocenters via thiourea-catalyzed asymmetric Michael–Henry cascade reactions

• Yonglei Du,
• Jian Li,
• Kerong Chen,
• Chenglin Wu,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2017, 13, 1342–1349, doi:10.3762/bjoc.13.131

• spirocyclopentaneoxindoles. Keywords: asymmetric synthesis; four consecutive stereocenters; Michael–Henry cascade reactions; spirocyclopentaneoxindoles; thioureas; Introduction The spirocyclic oxindole core represents an important scaffold that is encountered frequently in many biologically active molecules and natural

• spirocyclopentaneoxindoles containing multiple contiguous stereocenters remains challenging [23][24][25][26]. The medicinal properties of these frameworks mean that fast enrichment of spirooxindoles bearing diverse functional groups is of considerable importance. Recently, an increasing number of asymmetric catalysis

• asymmetric catalytic synthesis of saturated spirocyclopentaneoxindoles containing four consecutive stereocenters with 3-substituted oxindoles and nitrovinylacetamide using a bifunctional thiourea catalyst in good yields (up to 95%) with excellent diastereoselectivity (up to 3:97) and enantioselectivity (up

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

• Stephan Scheeff and
• Dirk Menche

Beilstein J. Org. Chem. 2017, 13, 1085–1098, doi:10.3762/bjoc.13.108

• characteristic (Z,Z,E)-triene, a thiazole side chain and a characteristic sequence of eight methyl and hydroxy-bearing stereocenters. Synthetic chemistry is of key importance to enhance the supply of these scarce polyketides to fully evaluate the biological potential and develop them as potential drug candidates

Polyketide stereocontrol: a study in chemical biology

• Kira J. Weissman

Beilstein J. Org. Chem. 2017, 13, 348–371, doi:10.3762/bjoc.13.39

• functionality in a defined way in three dimensions, allowing them to bind their biological targets with useful affinity (10−7 to 10−9 M [4]). Erythromycin A (1, Figure 1) is the prototypical polyketide, as its biosynthesis has been studied most heavily to date. The structure incorporates 10 stereocenters, and

Highly chemo-, enantio-, and diastereoselective [4 + 2] cycloaddition of 5H-thiazol-4-ones with N-itaconimides

• Shuai Qiu,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2016, 12, 2293–2297, doi:10.3762/bjoc.12.222

• ) were obtained for a series of spirocyclic 1,4-sulfur-bridged piperidinone-based succinimides. Keywords: [4 + 2] annulation; asymmetric organocatalysis; dipeptide-based Brønsted bases; 5H-thiazol-4-ones; N-itaconimides; Introduction Sulfur-containing tetrasubstituted carbon stereocenters are widely

An effective one-pot access to polynuclear dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties via a 1,3-dipolar cycloaddition strategy

• Alexei N. Izmest’ev,
• Galina A. Gazieva,
• Natalya V. Sigay,
• Sergei A. Serkov,
• Valentina A. Karnoukhova,
• Vadim V. Kachala,
• Alexander S. Shashkov,
• Igor E. Zanin,
• Angelina N. Kravchenko and
• Nina N. Makhova

Beilstein J. Org. Chem. 2016, 12, 2240–2249, doi:10.3762/bjoc.12.216

• of the stereocenters of compounds 4 are 2’R*, 3aS*, 3’R*, 4’R*, 9aR*. The homogeneity of compounds 4b–d,f–i,l–n was additionally confirmed by powder X-ray diffraction. The analysis of the experimental powder diffraction patterns of compounds 4b–d,f–i,l–n show that the investigated samples were single

• diastereomer is obtained in good to high yields, although multiple (five) stereocenters are present in products 4. The possible approaches of the azomethine ylide are shown in Figure 8. The X-ray diffraction structures of 4c, 4e, and 4r reflect that the cycloaddition proceeds via an exo-transition state

Chiral ammonium betaine-catalyzed asymmetric Mannich-type reaction of oxindoles

• Masahiro Torii,
• Kohsuke Kato,
• Daisuke Uraguchi and
• Takashi Ooi

Beilstein J. Org. Chem. 2016, 12, 2099–2103, doi:10.3762/bjoc.12.199

• efficient construction of vicinal quaternary and tertiary stereocenters [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In particular, the application of 3-aryl substituted oxindoles seems problematic; hence, the full potential of this useful carbon–carbon bond formation is yet to be realized [12

• -butylphenyl group, delivered a critical improvement in diastereoselectivity, affording 4aa quantitatively and establishing consecutive quaternary and tertiary stereocenters with almost complete fidelity (Table 1, entry 3). Further examination of the reactions under the influence of 1d, having 3,5-bis

• the scope of this mode of stereoselective Mannich-type reaction, which involve the generation of vicinal quaternary and tertiary stereocenters. Further investigations into the potential utility of ammonium betaine catalysis are underway in our laboratory. Chiral ammonium betaines. ORTEP diagram of 4ca

Enantioconvergent catalysis

• Justin T. Mohr,
• Jared T. Moore and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2016, 12, 2038–2045, doi:10.3762/bjoc.12.192

• . Deuterium labeling experiments have shown that the hydrogenation reaction occurs only on the chiral keto tautomer, and therefore the catalyst selects one enantiomer of the substrate when the reduction takes place. Enantioconvergent methods are not limited to carbon stereocenters. An exceptional example of

• reaction was reported by Stoltz for the generation of enantioenriched all-carbon quaternary stereocenters from racemic allyl β-ketoesters (e.g., (±)-20 → (+)-23, Scheme 5) [29]. This particular reaction is especially unusual since the stereoablative step requires scission of a C–C bond at a quaternary

Application of heterocyclic aldehydes as components in Ugi–Smiles couplings

• Katelynn M. Mason,
• Michael S. Meyers,
• Abbie M. Fox and
• Sarah B. Luesse

Beilstein J. Org. Chem. 2016, 12, 2032–2037, doi:10.3762/bjoc.12.191

• Diels–Alder (US-IMDA) reaction with substituted 2-furaldehyde and allylamine (Scheme 1), which provides direct access to N-arylepoxyisoindolines 1 through a simple, one-pot reaction [23]. Through this stereoselective tandem process, six new bonds and four stereocenters are generated in one synthetic

Bridgehead vicinal diallylation of norbornene derivatives and extension to propellane derivatives via ring-closing metathesis

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2016, 12, 1877–1883, doi:10.3762/bjoc.12.177

• compound 2a was formed from the corresponding O-allyl compound via CR. Based on the X-ray structure of 1a and the above observations, it is clear that the allyl groups in 2a are in endo configuration which can be explained as follows. Since the stereocenters are unaffected during the RCM sequence it is

Synthesis of the C8’-epimeric thymine pyranosyl amino acid core of amipurimycin

• Pramod R. Markad,
• Navanath Kumbhar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2016, 12, 1765–1771, doi:10.3762/bjoc.12.165

• attack of the secondary hydroxy group to the oxocarbenium ion Y led to a stable six-membered pyranose ring compound thus shifting the equilibrium in favour of bridged bicyclic system 12/13. In order to validate the configurational assignments at the newly generated stereocenters, the coupling constants

• configuration at the newly generated stereocenters at C5’ and C6’ (corresponding to the C7 and C8 of epoxide 8) [20]. In the 1H NMR of 14, appearance of a triplet at δ 2.30 (J = 12.7 Hz) and a doublet of doublet at δ 2.09 (J = 12.7 and 4.7 Hz), integrating for one proton each, were assigned to the methylene

• orientation indicating 5’S absolute configuration as anticipated from the SAE mnemonic in compound 8. As the C5’ and C6’ stereocenters in 14 are derived from the regioselective SN2 opening of epoxide 8 by NaN3, the configuration at the C6’ (carrying azido group) was therefore assigned as 6’R. In the 1H NMR

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• researchers have developed methods for the stereoselective synthesis of tertiary carbon stereocenters. One aesthetically pleasing approach is the enantioselective protonation of prochiral enolates and enolate equivalents [1][2][3][4][5][6][7][8][9][10]. While an attractive strategy, the enantioselective

• additions to other classes of Michael acceptors only being reported more recently. While many examples using sulfur and carbon nucleophiles have been reported, the addition of other heteroatom nucleophiles remains relatively unexplored. This approach for the synthesis of tertiary carbon stereocenters

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• asymmetric ruthenium-catalyzed cycloisomerization reactions in the literature. In 2011, our research group disclosed the ruthenium-catalyzed redox bicycloisomerization of 1,6- and 1,7-enynes to construct structurally complex [3.1.0] and [4.1.0] bicycles containing vicinal, quaternary all-carbon stereocenters