An efficient synthesis of the guaiane sesquiterpene (−)-isoguaiene by domino metathesis

• Yuzhou Wang,
• Ahmed F. Darweesh,
• Patrick Zimdars and
• Peter Metz

Beilstein J. Org. Chem. 2019, 15, 858–862, doi:10.3762/bjoc.15.83

• olefin 14 delivered aldehyde 4 with considerably higher efficiency compared to the known six-step preparation of ent-4 from (−)-menthone [21]. Asymmetric Michael addition [7][8][10] of aldehyde 4 to methyl vinyl ketone (15) proceeded with high catalyst-controlled diastereoselectivity (dr = 23:1) to yield

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• imidazopyridine-containing biaryls via central-to-axial chirality transfer (Scheme 1). Results and Discussion The substituents on the phenyl ring (R1) and at the propargylic position (R2) of carbamate 2 were varied to study their effects on the diastereoselectivity (Table 1). The electrolysis was conducted under

• imidazopyridine-based biaryl 3a in 68% yield with good diastereoselectivity (14:1 dr). Replacing the t-Bu group at the propargylic position with iPr (Table 1, entry 2) or on the phenyl ring with Ph (Table 1, entry 3) or OiPr (Table 1, entry 4) all resulted in low diastereoselectivity (2:1 to 3:1). The scope of

• tolerated albeit with reduced diastereoselectivity. The t-Bu group on the phenyl ring and at the propargylic position could be replaced with other bulky tertiary substituents to afford a range of functionalized biaryl products (3p–w). The electrochemical conditions were compatible with several functional

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

• achieve good diastereoselectivity during the carbometalation reaction, few conditions needed to be fulfilled in the design of the starting cyclopropenyl ring (Figure 1): The presence of a coordinating group (such as an oxygen) at the C3 position is crucial for the selective facial addition of the incoming

• different types of cyclopropene precursors. We concentrated our efforts on the reaction of diversely substituted 3-methyl-3-arylcyclopropenes 6. In this case, as there is no coordinating functionality to dictate the facial selectivity, the control of the diastereoselectivity may be more challenging

A chemoenzymatic synthesis of ceramide trafficking inhibitor HPA-12

• Seema V. Kanojia,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2019, 15, 490–496, doi:10.3762/bjoc.15.42

• -alcohol [53]. However, unlike in our case, the reaction proceeded with poor diastereoselectivity irrespective of the dihydroxylating agent used. To confirm the 1,3-anti diol stereochemistry of 7a, it was debenzylated using DDQ/CH2Cl2–H2O to furnish the trihydroxy compound 7a'. The 1H and 13C NMR spectra

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• ]. Subsequent oxidation of radical 7 by Cu(II) affords a formally cationic intermediate that is trapped by the carbamoyl oxygen to afford oxonium 8. The loss of the tert-butyl cation provides the oxyamination product 2, which can be isolated in good yields with excellent diastereoselectivity. Turnover of 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

• -position of the aromatic group at C3 significantly affected the diasteomeric ratio with an increase observed with the mesomeric donor methoxy group in favor of diastereomer 7b (7b/7’b = 78:22) compared to 7a/7’a, and a drop of diastereoselectivity when a fluorine atom (7c/7’c = 60:40) or a hydrogen atom

• diastereoselectivity. However, the sigmatropic rearrangement of the highly hindered di(tert-butyl)phosphinite 6j and tetra(isopropyl) phosphorodiamidite 6k did not occur (Scheme 7) [37]. The mechanism proposed by Rubin et al. involves a reversible addition of the Lewis base (DBU) on the cyclopropene double bond at C2

• activation barriers of the reactions leading to 8 and 8’, regardless of the aromatic substituent. Since 8 and 8’ were in rapid equilibrium with phosphinite 6, the diastereoselectivity should depend on the relative stabilities of the transition states TS1 and TS’1. An electron-donating group at the para

Synthesis of 1,2-divinylcyclopropanes by metal-catalyzed cyclopropanation of 1,3-dienes with cyclopropenes as vinyl carbene precursors

• Jesús González,
• Alba de la Fuente,
• María J. González,
• Laura Díez de Tejada,
• Luis A. López and
• Rubén Vicente

Beilstein J. Org. Chem. 2019, 15, 285–290, doi:10.3762/bjoc.15.25

• proceeded in reasonable yields while the diastereoselectivity strongly depends on the structure of the diene. An example of an intramolecular process as well as the use of furan and 1,4-cyclohexadiene as dienes are also reported. Keywords: cyclopropanation; cyclopropenes; dienes; divinylcyclopropanes

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• carbonyl group. Thus, when compound 40 prepared using readily available (S)-(+)-ketopinic acid was reacted with phenylselenyl chloride in methanol the adduct 41 was formed with high diastereoselectivity (de 96%) and was later separated chromatographically. Further transformations into dimethyl ester of (2S

• electrophilic hydroxylation at C4 When the lithium enolate of dimethyl N-Cbz-L-glutamate 63 was treated with Davis oxaziridine, an inseparable 9:1 mixture of diastereoisomers was formed with (2S,4S)-64 predominating (Scheme 16) [74]. For sodium and potassium enolates diastereoselectivity of the hydroxylation

Gold-catalyzed ethylene cyclopropanation

• Silvia G. Rull,
• Andrea Olmos and
• Pedro J. Pérez

Beilstein J. Org. Chem. 2019, 15, 67–71, doi:10.3762/bjoc.15.7

• exquisite control of chemo-, enantio- and/or diastereoselectivity being achieved [1][2]. Previous developments have involved a large number of C=C-containing substrates but, to date, the methodology has not been yet employed with the simplest olefin, ethylene, for synthetic purposes [3]. Since diazo

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• improve E/Z selectivity in CM reactions and diastereoselectivity in RCM reactions altering the environment of key metathesis intermediates. Complexes 24 and 25 were found to exist in solution as a single rotational isomer having the benzylidene moiety located under the mesityl group, and for complexes 24b

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• ) [35]. Indeed, the reaction of achiral pinacol (Z)-crotylboronate with 5 under neat conditions at room temperature gave a good level of diastereoselectivity for the hitherto unreported 3,4-syn-2,3-anti product 12b [36][37][38][39]. The syn relationship between C3 and C4 is controlled by the (Z

Green synthesis of new chiral 1-(arylamino)imidazo[2,1-a]isoindole-2,5-diones from the corresponding α-amino acid arylhydrazides in aqueous medium

• Nadia Bouzayani,
• Jamil Kraїem,
• Sylvain Marque,
• Yakdhane Kacem,
• Abel Carlin-Sinclair,
• Jérôme Marrot and
• Béchir Ben Hassine

Beilstein J. Org. Chem. 2018, 14, 2923–2930, doi:10.3762/bjoc.14.271

• state becomes unlikely and then the selectivity is important. Our model is in agreement with the diasteroisomeric ratio results. In fact, a total diastereoselectivity was observed, including 5d (R = Ph) since an epimerization of the initial asymmetric center was observed, therefore racemic trans-isomers

• observed with a total trans-diastereoselectivity controlled by intramolecular hydrogen bonds. Chemical structures of analogues. NOEs correlation showing the stereochemistry of the compound 5a. X-ray crystal structure of 5f shown at the 30% probability level. Strategy for the formation of 1-(arylamino)-1H

Synthesis of α-D-GalpN₃-(1-3)-D-GalpN₃: α- and 3-O-selectivity using 3,4-diol acceptors

• Emil Glibstrup and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2018, 14, 2805–2811, doi:10.3762/bjoc.14.258

• acceptors and donors are made from common building blocks, limiting protective manipulations, and in this context, unavoidable side reactions. Keywords: diastereoselectivity; glycosylation; regioselectivity; Introduction The disaccharide α-D-GalpNAc-(1-3)-β-D-GalpNAc is a widespread motif in glycobiology

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• stereoselectivity of the ring-formation step can be explained by the suprafacial addition of the allene to the double bond of the α,β-unsaturated compound 4, the diastereoselectivity being sterically controlled by the methyl group on the β-face. The transformation of the vinylsilane moiety in 5 into the

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• structures present in compounds 2–6. In addition, we expected that the higher hydrogen count and the non-planarity of the envisaged 1,3-cyclohexadiene ring would allow the determination of the diastereoselectivity of the coupling step more precisely than in the case of aromatic 8 that exists as mixture of

• diastereoselectivity, which means that every single example has to be explored independently. The assignment of the configuration and preferred conformation of product 18 was conducted on the basis of NOESY NMR experiments. Our analysis was aided by the observation that the 2-epimer 19 was accessible by oxidation of

Microfluidic light-driven synthesis of tetracyclic molecular architectures

• Javier Mateos,
• Nicholas Meneghini,
• Marcella Bonchio,
• Nadia Marino,
• Tommaso Carofiglio,
• Xavier Companyó and
• Luca Dell’Amico

Beilstein J. Org. Chem. 2018, 14, 2418–2424, doi:10.3762/bjoc.14.219

• commercially available precursors and a common 365 nm bulb. The reaction does not proceed under conventional batch conditions, highlighting the essential role of the developed MFP. A wide series of naphthochromenones and benzoxanthenes were synthesized in high yields and excellent diastereoselectivity. Finally

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

• Piotr Pomarański,
• Piotr Roszkowski,
• Jan K. Maurin,
• Armand Budzianowski and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2018, 14, 2384–2393, doi:10.3762/bjoc.14.214

• , both in ortho-methoxyphenyl and ortho-chlorophenyl series (Figure 5 and Figure 6). In the former one, however, the successive arylation is additionally affected by apparent O-chelation of the metal at the transition state which results in noticeable diastereoselectivity of this process, leading to a

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• *(C6H6)][B(C6F5)4]2 and LiOAc gave alcohol products 62 with high diastereoselectivity at ambient reaction conditions. The unique nature of cobalt was well presented by its superior reactivity and diastereoselectivity and it outmatched the rhodium catalyst. Different pyrazole derivatives with a wide range

Bi-mediated allylation of aldehydes in [bmim][Br]: a mechanistic investigation

• Mrunesh Koli,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2018, 14, 2198–2203, doi:10.3762/bjoc.14.193

• alcohol 2l' was obtained as the major diastereomer (Table 2, entry 11), although the reaction diastereoselectivity was inferior to that by the Luche’s protocol using Zn metal [42]. In all the reactions, the products were easily isolated by extracting the reaction mixture three times with Et2O followed by

Cobalt-catalyzed nucleophilic addition of the allylic C(sp³)–H bond of simple alkenes to ketones

• Tsuyoshi Mita,
• Masashi Uchiyama,
• Kenichi Michigami and
• Yoshihiro Sato

Beilstein J. Org. Chem. 2018, 14, 2012–2017, doi:10.3762/bjoc.14.176

• at 60 °C in DMA according to our previously established catalytic conditions (Co(acac)2 (10 mol %), Xantphos (20 mol %), and AlMe3 (1.0 equiv)) [29], branched homoallylic alcohol 3aa was obtained in only 23% yield with 1.6:1 diastereoselectivity (Table 1, entry 1). In constant to the C(sp3)–H

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• the presence of acetic anhydride [46]. As the peroxy compounds can react with alkenes, leading to the anti-products via epoxy intermediates, substrates must be added slowly by a syringe pump to provide reasonable yields and diastereoselectivity. The diastereoselectivity of the reaction can be

• diastereoselective catalytic fluorination was developed by the same group (Scheme 14, bottom) [65] using the lactate-based resorcinol derivative 44 as the catalyst. By this route chiral 4-fluoroisochromanones 46 could be accomplished in high enantio- and diastereoselectivity. The same I(III) intermediate 47 was

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• 98% to afford α-benzoyloxy propargylic derivatives 39. Again the strategy can be applied to the late-stage modification of steroids with high levels of diastereoselectivity. λ3-Iodane reagents: azidobenziodoxolone (ABX) and chlorobenziodoxolone In a similar manner to the previously described

• the limiting components, with nearly quantitative yields and complete diastereoselectivity [102][103][104][105]. Such a highly efficient atom-transfer process has provided the opportunity to design a tandem of C–N and C–C bond-forming reactions that relies on an initial step of catalytic nitrene

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst

• Kimihiro Komeyama,
• Shunsuke Sakiyama,
• Kento Iwashita,
• Itaru Osaka and
• Ken Takaki

Beilstein J. Org. Chem. 2018, 14, 1413–1420, doi:10.3762/bjoc.14.118

• % yield with a diastereoselectivity ratio of 92:8 (Table 1, entry 13). Additionally, preformed CoBr2(L3) gave a similar result (Table 1, entry 14). During the transformation, the chromium catalyst ligands inhibited the reaction (Table 1, entries 15–17). Also, the reaction was highly dependent on the

• good yields (Scheme 8). During the investigation of allenes, it was observed that, when oxygen substituents were present at the allenyl position, coupling products with reversed diastereoselectivity were obtained (Scheme 9). Thus, treatment of 4-benzyloxybuta-1,2-diene (5) with 1 and 3a under identical

• reaction conditions mainly afforded the anti-configured homoallylic alcohols 7–10 in 46–65% yield. A similar reversed diastereoselectivity was observed in the coupling reaction of silyloxy allene 6, leading to 11 in 46% yield (anti/syn = 73:27). A stoichiometric reaction using phenylchromium(II or III

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• -substituted benzaldehydes gave the best enantioselectivity, and the desired aldol products were obtained with anti diastereoselectivity (Scheme 26). In addition, when DMF was used as solvent, a positive effect on the enantioselectivity but negative effect on the diastereoselectivity were observed. The

• aldol reaction between 21 and 70 and offered superior diastereo- and enantioselectivities in the presence of chloroacetic acid (96% conversion, 86:14 anti diastereoselectivity and 73% ee) (Scheme 25). Under the optimum reaction media, a series of diverse benzaldehydes bearing electron withdrawing groups

• activity and stereoselectivity of catalyst 99. As shown in Figure 11, this catalytic system renders to use the calixarene cavity and in consequence of this both the high diastereoselectivity and enantioselectivity can be explained. Furthermore, when 99 used in 2 mol % can be recycled easily and re-used six

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

• diastereoselectivity of 90% de was achieved in the reaction of 1-benzoylacetone (R2 = Me, R3 = Ph) which afforded the corresponding single diastereoisomeric product in 96% yield and 95% ee. In 2018, Tanyeli et al. reinvestigated this type of reactions in the presence of related cinchona alkaloid-derived squaramide

• (34–80% de). The lowest diastereoselectivity (34% de) was obtained in the reaction of a disubstituted substrate (R1 = 4,7-Cl2), showing that it was sensitive to the substitution of the aryl moiety of the isatin. In fact higher diastereoselectivities (≥60% de) were achieved for all other substrates