Synthesis and biological evaluation of 1,2-disubstituted 4-quinolone analogues of Pseudonocardia sp. natural products

• Stephen M. Geddis,
• Teodora Coroama,
• Suzanne Forrest,
• James T. Hodgkinson,
• Martin Welch and
• David R. Spring

Beilstein J. Org. Chem. 2018, 14, 2680–2688, doi:10.3762/bjoc.14.245

• natural products. The chemistry developed towards the allylic alcohols 5 and 6, outlined in Scheme 1, seemed ideal to this end. A range of alkynes 10 could undergo Sonogashira coupling with the commercially available acid chloride 9. The resultant ynones 11 could then undergo conjugate addition with

• resulted for 11b, which was attributed to difficulties in obtaining its precursor 10b with high purity which stemmed from its volatility. These ynones were then subjected to a conjugate addition with an assortment of primary amines 12a–f (Scheme 3). The reactions proceeded with excellent yield in all cases

• -quinolone Pseudonocardia sp. natural products, which encompassed variation of both the side chain and N-substituent. This represented an extension of the chemistry which we employed towards the natural products, utilising sequential Sonogashira coupling, high-yielding conjugate addition, and metal-catalysed

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• the enolate intermediate 111 followed by the generation of a C–C bond via conjugate addition delivered intermediate carbene 113. A 1,2-hydrogen shift led to the formation of products 108 with enantioselectivities up to 79% (Scheme 24). Later, Maruoka et al. improved the enantioselectivity up to 95% ee

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• as a fairly air-stable red-brown solid. b. Nucleophilic addition to 4,5-benzotropone (11): Ried’s group realized the reaction of 4,5-benzotropone (11) and its derivatives with lithium acetylide as a nucleophile between −50 and −32 °C [130]. While the possible 1,4-conjugate addition product 149 was

Gram-scale preparation of negative-type liquid crystals with a CF₂CF₂-carbocycle unit via an improved short-step synthetic protocol

• Tatsuya Kumon,
• Shohei Hashishita,
• Takumi Kida,
• Shigeyuki Yamada,
• Takashi Ishihara and
• Tsutomu Konno

Beilstein J. Org. Chem. 2018, 14, 148–154, doi:10.3762/bjoc.14.10

• the 1,2-addition reaction of Int-I proceeds in preference to the conjugate addition reaction, the desired octa-1,7-diene 5a should be produced in higher yield. However, no significant improvement was observed after various attempts such as employing a more nucleophilic lithium reagent instead of the

• the other hand, the β-carbon at the α,β-unsaturated carbonyl moiety of Int-I may be susceptible to attack by the vinylic Grignard reagent, as shown by the purple arrow in Scheme 3, because of the high electrophilicity and lack of steric hindrance. As a consequence, Int-I also undergoes conjugate

• addition reaction, a Michael addition reaction, giving rise to the corresponding magnesium enolate Int-L. The subsequent hydrolysis of Int-L then leads to the γ-hydroxyketone 8a', which easily tautomerizes into the more stable 5-membered hemiacetal 8a. From the above insight into the reaction mechanism, if

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• acceptors in organic synthesis [1][2][3][4][5]. Unlike the parent α-nitroalkenes, α-nitrosoalkenes are unstable species usually generated in situ, and their synthetic potential has been studied in significantly less detail [6][7]. Because of relatively short lifetimes of α-nitrosoalkenes, conjugate addition

• years, there has been a considerable growth of interest to the conjugate addition of carbon-centered nucleophiles to α-nitrosoalkenes. This is mainly due to the development of new precursors, from which nitrosoalkenes are generated at low stationary concentrations under very mild conditions that allows

• the potential use of this strategy in the synthesis of natural products. Weinreb and co-workers performed a comprehensive investigation of the stereoselectivity of the conjugate addition to α-nitrosoalkenes using both cyclic [29] and acyclic substrates [30]. They have demonstrated that the

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

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• intramolecular conjugate addition to an α,β-unsaturated ester [12][13][14][15] or copper-catalyzed annulation of N-arylamidines [41], among others [42]. Most of the already mentioned methods have been applied to the synthesis of 3,4-dihydroquinazolines. Among them, only a few were used for the preparation of 1,4

Phosphazene-catalyzed desymmetrization of cyclohexadienones by dithiane addition

• Matthew A. Horwitz,
• Elisabetta Massolo and
• Jeffrey S. Johnson

Beilstein J. Org. Chem. 2017, 13, 762–767, doi:10.3762/bjoc.13.75

• Matthew A. Horwitz Elisabetta Massolo Jeffrey S. Johnson Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA 10.3762/bjoc.13.75 Abstract We report a desymmetrization of cyclohexadienones by intramolecular conjugate addition of a tethered dithiane

• nucleophile. Mild reaction conditions allow the formation of diversely functionalized fused bicyclic lactones. The products participate in facially selective additions from the convex surface, leading to allylic alcohol derivatives. Keywords: conjugate addition; cyclohexadienones; dearomatization

• ] nucleophiles using bifunctional cinchona alkaloid catalysts. The Sasai and Enders groups used a phosphinothiourea to enable a Rauhut–Currier reaction to form bicyclic enones [16]. The Tian and Lin group used alkyne-tethered cyclohexadienones in an arylrhodation/conjugate addition sequence that

Solid-phase enrichment and analysis of electrophilic natural products

• Frank Wesche,
• Yue He and
• Helge B. Bode

Beilstein J. Org. Chem. 2017, 13, 405–409, doi:10.3762/bjoc.13.43

• calculated mass of 3 (Figure 1) derived from the derivatization of epoxystilbene 1, an oxidized isopropylstilbene derivative from this strain. Since only a single peak could be seen within the chromatogram, we assume that the conjugate addition took place only on the less hindered position in epoxide 1

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• substituted carbocycles [119][120]. An example in described in Scheme 22. The 5-membered ring is formed via a K2CO3 mediated SN2 – conjugate addition sequence between malononitrile and 6-bromo-2-hexenoate derivatives 67a,b. Dicyanocyclopentanes 68a,b are treated with tributyltin hydride/AIBN giving the

First DMAP-mediated direct conversion of Morita–Baylis–Hillman alcohols into γ-ketoallylphosphonates: Synthesis of γ-aminoallylphosphonates

• Marwa Ayadi,
• Haitham Elleuch,
• Emmanuel Vrancken and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2906–2915, doi:10.3762/bjoc.12.290

• were prepared by reductive amination of γ-aminophosphonyl ketones using sodium borohydride [41], or by conjugate addition of diethyl methylphosphonite to 2-cyclohexenone followed by Bucherer–Bergs amino acid synthesis [42]. Another synthetic approach for a series of α-fluorinated-γ-aminophosphonates

• , entries 1–5), as well as five-membered cyclic MBH alcohol 1f (Table 2, entry 6). A putative reaction pathway could start from a first β-conjugate addition of DMAP onto the allylic alcohol 1a (i), followed by the elimination of the hydroxide ion that would afford the intermediate I (ii). Similarly, a

• second β’-conjugate addition of triethyl phosphite onto I (iii), followed by the release of DMAP would provide the phosphonium intermediate II (iv). Finally, the hydroxide ion is expected to react with II via an Arbuzov rearrangement to provide the desired γ-ketoallylphosphonate 2a (v) (Scheme 3). We

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• directionality that might make these interactions of a great value to the field of organocatalysis [71][72][73]. Molecular iodine has been used for many decades as a mild catalyst or promoter of various organic transformations such as conjugate addition, imine formation or aldolate dehydration reactions [74][75

• -workers have re-evaluated the molecular iodine-catalyzed conjugate addition to α,β-unsaturated carbonyls or nitrostyrenes (Scheme 14) [80]. Based on their computational studies, they proposed that iodine activates the enone moiety by forming a halogen bond with the carbonyl and thus forming a more

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

• Ahlem Abidi,
• Yosra Oueslati and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2402–2409, doi:10.3762/bjoc.12.234

• -allylated product 3j in 12% yield, along with the tricyclic compound 6j, in good yield, which is resulting from the intramolecular conjugate addition of 3j carbanion on the enone moiety (Table 3, entry 2). Under the same conditions, the keto ester 2j reacted with alcohol 1a, in DMF at 80 °C for 6 h longer

• conjugate addition of the β-keto ester carbanion onto the enone moiety (Scheme 2) [50][51]. The structure of the tricyclic compound 6j was elucidated on the basis of X-ray diffraction analysis (Figure 2). In a previous report, Alexakis and co-workers have demonstrated that copper-catalyzed conjugate

• addition of Grignard reagents onto α-methyl cyclic enones, affording mainly the trans-2,3-disubstituted cyclohexanones as being the thermodynamic products [52]. Similarly, we believe that the intramolecular conjugate addition of carbanion 3j onto α-substituted enone moiety is under thermodynamic control

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

• class of sulfur-containing pro-nucleophiles in a highly enantio- and diastereoselective conjugate addition to nitroalkenes, providing α,α-disubstituted α-mercapto carboxylic acids [5]. Since then, several asymmetric variants using 5H-thiazol-4-ones as nucleophiles have been disclosed; such as amination

• [6], allylation [7], conjugate addition to enones [8], and γ-addition with allenoates [9]. All these examples focused on nucleophilic addition reactions of the C5 atom of 5H-thiazol-4-ones. Recently, we described an organocatalytic asymmetric [4 + 2] cyclization of 5H-thiazol-4-ones with a series of

• excellent catalytic efficacy as demonstrated in a series of asymmetric reactions [18]. It was found that the reaction was completed after 48 hours, affording the desired [4 + 2] annulation adduct 3a in 55% yield with 64% ee. A significant amount of conjugate addition adduct led to the unsatisfactory

p-Nitrophenyl carbonate promoted ring-opening reactions of DBU and DBN affording lactam carbamates

• Madhuri Vangala and
• Ganesh P Shinde

Beilstein J. Org. Chem. 2016, 12, 2086–2092, doi:10.3762/bjoc.12.197

• products [12]. Subsequently, Ma and Dolphin isolated chlorin-e6 lactams from the reaction of methyl pheophorbide with DBU and DBN promoted by trialkyl triflates [13]. Additionally, the conjugate addition reaction of DBU to diarylpyrone [14] and Baylis–Hillman acetates [15] also gave caprolactam products. A

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• they differ by a central, annelated furan-3-one moiety instead of an acrylate unit (Scheme 25) [149]. Their biosynthesis proceeds from chalcones by an oxidation–conjugate addition cascade catalysed by plant phenol oxidases (PPOs) [150][151]. The PPO aureusidin synthase plays a central role in aurone

• biosynthesis in Antirrhinum majus [152][153]. It catalyses the oxidation of phenols 180 and o-catechols 181 to o-quinones 182 and concomitant conjugate addition of a phenolic hydroxy group, leading to the formation of the central furan-3-one unit [154]. This enzyme is flavin-dependent and acts under

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

• are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals. Keywords: asymmetric catalysis; conjugate addition; enantioselective protonation; enolate; Introduction Due to their ubiquity in natural products and drugs, many

• -stereoselective step allows for the generation of a prochiral enolate intermediate that then undergoes enantioselective protonation (Figure 1). Two general strategies can be used when applying a conjugate addition–enantioselective protonation manifold. In the first strategy, a chiral enolate can be protonated by

• an achiral proton source (pathway A). In the second, an achiral enolate can be protonated by a chiral proton source (pathway B). Both strategies have been harnessed by various research groups for conjugate addition–enantioselective protonation reactions. This review covers the many conjugate addition

1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis

• Antonia Mielgo and
• Claudio Palomo

Beilstein J. Org. Chem. 2016, 12, 918–936, doi:10.3762/bjoc.12.90

• )-ones 1 as pronucleophiles in organocatalyzed Michael addition reactions 2-Thio-1H-imidazol-4(5H)-ones 1 (R = SBn) have been reported to be effective equivalents of N-subtituted (alkyl, aryl, allyl) α-amino acids in conjugate addition reactions to both, nitroalkenes and α-silyloxy enones as Michael

• published [73]. This study shows that α’-oxyenones are very efficient key enoate equivalents in Brønsted base-catalyzed asymmetric conjugate addition of a range of soft nucleophiles such as α-substituted oxindoles, cyanoesters, oxazolones, azlactones and thiazolones to afford the corresponding

The aminoindanol core as a key scaffold in bifunctional organocatalysts

• Isaac G. Sonsona,
• Eugenia Marqués-López and
• Raquel P. Herrera

Beilstein J. Org. Chem. 2016, 12, 505–523, doi:10.3762/bjoc.12.50

• % of this compound was employed in the enantioselective conjugate addition of the hydroxylamine derivatives 31 to the enoates 30, affording the final products 32 with good yield (up to 98%) and high enantiomeric excess (up to 98% ee). This provided an efficient method that allows the preparation of

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• Mannich–Michael pathway instead of the more “reasonable” Michael–Mannich pathway. In 2012, Wang and co-workers reported a novel domino Friedel–Crafts alkylation (via conjugate addition)-hemiacetalization catalyzed by rosin-derived tertiary amine-thiourea 187 (Scheme 61) [82]. Reagent 87 was successfully

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• cyclopropanation using dimethyl bromomalonate (57) and some form of Michael acceptor. In this process, the enolate resulting from the initital conjugate addition attacks the C–Br bond to form a three-membered ring. In our work in this area, we designed a new cupreine derived catalyst HCPN-59 to add dimethyl

• nitroolefins, and (b) Lin’s similar process with α-nitroesters using the symmetric hydrocupreidine system HCPD-44. A diastereodivergent sulfa-Michael addition developed by Melchiorre and co-workers. Melchiorre’s vinylogous Michael addition. Simpkins’s TKP conjugate addition reactions. Hydrocupreine catalyst

Synthesis and reactivity of aliphatic sulfur pentafluorides from substituted (pentafluorosulfanyl)benzenes

• Norbert Vida,
• Jiří Václavík and
• Petr Beier

Beilstein J. Org. Chem. 2016, 12, 110–116, doi:10.3762/bjoc.12.12

• transformations: electrophilic aromatic hydroxylation to the intermediate 6, oxidation to ortho-benzoquinone 7, Baeyer–Villiger (BV) oxidation, hydrolysis to muconic acid derivative 8, and finally intramolecular conjugate addition affording 3. Under certain conditions, small amounts of intermediates 6 and 8 were

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• already at that time the great potential of modern synthetic organic chemistry. More than 20 years later, in 1984, Oishi and co-workers reported a different strategy which culminated in the total synthesis of racemic β-caryophyllene (22) (Scheme 5) [34]. Their synthesis commenced with conjugate addition

• allenic sulfone [44] which, upon conjugate addition of diethyl amine followed by hydrolysis afforded a β-ketosulfone. For the following ring closure, the primary alcohol was desilylated and converted to the corresponding allylic carbonate 71. The cyclononene structure 72 was then assembled via a palladium

• -catalyzed conjugate addition of silyl ketene acetal 81a to enone ent-80. Deprotonation and trapping of the resulting enolate with formaldehyde furnished lactone 82 in a regio- and stereoselective fashion. Introduction of the exocyclic double bond proved to be challenging and therefore salt-free, highly

Copper-catalyzed stereoselective conjugate addition of alkylboranes to alkynoates

• Takamichi Wakamatsu,
• Kazunori Nagao,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2015, 11, 2444–2450, doi:10.3762/bjoc.11.265

• Takamichi Wakamatsu Kazunori Nagao Hirohisa Ohmiya Masaya Sawamura Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan 10.3762/bjoc.11.265 Abstract A copper-catalyzed conjugate addition of alkylboron compounds (alkyl-9-BBN, prepared by hydroboration of

• alkenes with 9-BBN-H) to alkynoates to form β-disubstituted acrylates is reported. The addition occurred in a formal syn-hydroalkylation mode. The syn stereoselectivity was excellent regardless of the substrate structure. A variety of functional groups were compatible with the conjugate addition

• . Keywords: alkylborane; alkynoate; conjugate addition; copper; multisubstituted alkene; Introduction Copper-mediated conjugate additions of organometallic reagents to alkynoates are powerful tools for the synthesis of multisubstituted alkenes [1][2][3][4][5][6][7][8]. Because of their broad availability

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• Chimie, 8 Rue de l’Ecole Normale, 34296 Montpellier Cedex 5, France 10.3762/bjoc.11.263 Abstract The copper-catalyzed asymmetric conjugate addition (ACA) of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as

• ; sequential addition; Introduction Amongst the variety of synthetic methods available for the formation of C–C or C–heteroatom bonds, the asymmetric conjugate addition (ACA) of nucleophiles to electron-deficient alkenes is one of the most relevant and versatile for the synthesis of complex chiral molecules

• compound to an extended Michael acceptor was reported independently as early as 1972, by the Näf [4] and Corey [5] groups, who studied the reactivity of pentadienyl methyl ester (1, Figure 2). In both cases, the 1,6-conjugate addition of a stoichiometric amount of a Gilman reagent proceeded in a selective