Intermolecular addition reactions of N-alkyl-N-chlorosulfonamides to unsaturated compounds

• Gerold Heuger and
• Richard Göttlich

Beilstein J. Org. Chem. 2015, 11, 1226–1234, doi:10.3762/bjoc.11.136

• electrophilic themselves. Therefore we expected the addition to electron-rich enol ethers to proceed smoothly, however, with such electron-rich alkenes polar reaction pathways seem to become predominant (Table 3, entries 8 and 9). Whilst the formation of 11 from cyclohexene could result from an elimination of

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• This section will focus on Lewis acid-catalyzed ECA reactions, which employ stabilized nucleophiles such as silyl enol ethers and amines. Chiral Lewis acids play a dual role in these reactions. They activate the Michael acceptors by coordinating with the carbonyl oxygen and they provide a chiral

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• anodic oxidation of electron-rich olefins such as enol ethers 1 in methanolic solution generates radical cation 2 which can be used for a number of cyclization reactions (Scheme 2) [32][33]. Moeller et al. demonstrated that by intramolecular trapping of this highly reactive intermediate with a tethered

• coupling. In addition to enol ethers 1, vinyl sulfides and ketene acetals have successfully been cyclized according to Scheme 2 [34][35][36]. An interesting modification of this anodic coupling method was achieved by Yoshida, Nokami and co-workers using the “cation pool” concept [37][38][39]. In this

Atherton–Todd reaction: mechanism, scope and applications

• Stéphanie S. Le Corre,
• Mathieu Berchel,
• Hélène Couthon-Gourvès,
• Jean-Pierre Haelters and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2014, 10, 1166–1196, doi:10.3762/bjoc.10.117

• studied the enantioselective crossed aldol reaction of aldehydes with trichlorosilyl enol ethers. They obtained the aldol products in high yields with moderate to good enantioselectivities [101]. The chiral phosphoramidates used in this study and tested in many other enantioselective reactions (aldol

4-Hydroxy-6-alkyl-2-pyrones as nucleophilic coupling partners in Mitsunobu reactions and oxa-Michael additions

• Michael J. Burns,
• Thomas O. Ronson,
• Richard J. K. Taylor and
• Ian J. S. Fairlamb

Beilstein J. Org. Chem. 2014, 10, 1159–1165, doi:10.3762/bjoc.10.116

• part of our extensive studies on reactions involving 2-pyrone derivatives, we report herein a significant expansion of the Mitsunobu protocol to a variety of different coupling partners, along with an alternative route to the formation of 2-pyronyl enol ethers using an oxa-Michael addition to

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• University, Althanstrasse 14, A-1090 Vienna, Austria 10.3762/bjoc.10.70 Abstract Activated enol ethers derived from esters or the dinitrile of malonic acid, or from pentane-2,4-dione were treated with hydrazine hydrate. The structures of the obtained products – pyrazoles 5 – were studied with a focus on

• tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits. Keywords: bis-enehydrazines; enol ethers; NMR; pyrazole; tautomerism; Introduction Enol

• ethers are reactive species frequently used in organic synthesis [1]. They react predominantly with electrophiles. The introduction of one or more strong electron-withdrawing groups at the other end of the double bond from the alkoxy group causes an inversion of electron demand. These activated enol

Efficient carbon-Ferrier rearrangement on glycals mediated by ceric ammonium nitrate: Application to the synthesis of 2-deoxy-2-amino-C-glycoside

• Alafia A. Ansari,
• Y. Suman Reddy and
• Yashwant D. Vankar

Beilstein J. Org. Chem. 2014, 10, 300–306, doi:10.3762/bjoc.10.27

• synthesis of C-glycosides [12][13][14]. Among these, the Ferrier rearrangement [15] of glycals with protic acids [5][16][17] or Lewis acids [18][19][20][21][22] and carbon nucleophiles such as allylsilanes [23], silylacetylenes [24], silyl enol ethers [25], olefins [26], and organozinc reagents [27] has

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

• methodology [62][63][64]. The combination of the catalytic hetero-Diels–Alder/allyboration sequence with a ruthenium-catalyzed isomerization gave access to the 6,8-dioxabicyclo[3.2.1]octane skeleton of (+)-iso-exo-brevicomin (26, Scheme 18) [65]. When a Z/E mixture of 2-substituted enol ethers was used as

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• cycloheptadiene 265 via 264 in good yields. Further contributions to the topic have been put forward by the group of Echavarren [207] and Gung [208]. Cycloisomerization involving DVCPR Iwasawa and coworkers [209] discovered a cyclopropanation/DVCPR sequence of alkyne-substituted silyl enol ethers (for example 274

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• isomer in 10% yield (Scheme 43) [294]. The structures of these compounds were established by X-ray diffraction [294]. The cross-ozonolysis of enol ethers 172a,b with cyclohexanone enabled the synthesis of 1,2,4-trioxolanes 173a,b containing the easily oxidizable C–H fragment in the third position (Scheme

• unsymmetrical 1,2,4-trioxolanes, which are not accessible by direct ozonolysis of alkenes or the cross-ozonolysis of alkenes or enol ethers in the presence of carbonyl compounds. In addition, this method does not need tetrasubstituted alkenes or enol ethers as starting materials, which are difficult to prepare

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

• pentafluorosulfanylated compounds is constantly increasing [2], this expansion has not generally been accompanied by applications of these materials. Among aliphatic SF5-substituted compounds α-pentafluorosulfanylated aliphatic carbonyl compounds [16], readily prepared from the corresponding enol acetates or enol ethers

• SF5Cl to enol ethers and the subsequent acidic hydrolysis of 3. Formation of Schiff base 5 is problematic but, in contrast to the reactions of the analogous trifluoromethyl compounds, does successfully proceed. Even with a manifold of possible side reactions, β-lactam formation by the ketene–imine

• determined by single crystal X-ray diffraction studies. Thermal ellipsoids are set at 50% probability. (a) Complete structure of 7c. (b) PMP protecting group hidden for clarity. Synthesis of 2-pentafluorosulfanylaldehydes by addition of SF5Cl to enol ethers. Reaction of pentafluorosulfanylaldimines with

Gold(I)-catalyzed domino cyclization for the synthesis of polyaromatic heterocycles

• Mathieu Morin,
• Patrick Levesque and
• Louis Barriault

Beilstein J. Org. Chem. 2013, 9, 2625–2628, doi:10.3762/bjoc.9.297

• cyclization of non-cyclic enol ethers. As expected, the cyclization of enol ether 4 using [L2AuNCMe][SbF6] in dichloromethane afforded the cyclohexene 5 in 79% yield (Scheme 2). However, the anticipated 5-exo-dig product 6 was not observed when the catalyst [L1AuNCMe][SbF6] was utilized. Instead, the

• cyclizations of the enol ether 11a (R1 = p-BrC6H4, R2 = H) gave the corresponding benzothiophene 12a in 83% yield. The use of electron-poor silyl enol ether 11b (R1 = p-NO2C6H4, R2 = H) gave the desired product 12b, albeit in lower yield of 63%. Di- and trisubstituted silyl enol ethers 11c (R1 and R2 = H) and

Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

• Brian M. Casey,
• Dhandapani V. Sadasivam and
• Robert A. Flowers II

Beilstein J. Org. Chem. 2013, 9, 1472–1479, doi:10.3762/bjoc.9.167

• oxidation of several β-diketones and their related silyl enol ethers by CAN and the more lipophilic ceric tetra-n-butylammonium nitrate (CTAN) were measured in MeOH, MeCN and CH2Cl2 by using stopped-flow spectrophotometry [16]. In these experiments, initial oxidation of substrates generated radical cation

Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts

• Mostafa Kiamehr,
• Firouz Matloubi Moghaddam,
• Satenik Mkrtchyan,
• Volodymyr Semeniuchenko,
• Linda Supe,
• Alexander Villinger,
• Peter Langer and
• Viktor O. Iaroshenko

Beilstein J. Org. Chem. 2013, 9, 1119–1126, doi:10.3762/bjoc.9.124

• dielectrophiles has been a major research subject in both our laboratories. For example, we have studied reactions of quinolinium [36][37], isoquinolinium [38][39][40], quinazolinium [41][42] and quinoxalinium [43] salts with 1,3-bis(silyl enol ethers), i.e., masked 1,3-dicarbonyl compounds, which provided facile

• , which are subsequently cyclized by the addition of acid). In some cases the cyclization step failed, e.g., the reaction of 1,3-bis(silyl enol ethers) with pyridine in the presence of methyl chloroformate resulted in the formation of 1,4-dihydropyridines, which however, could not be cyclized by the

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• as 3 (R2 = alkyl) were employed in various synthetic transformations [6][7] (Scheme 1). In addition, Denmark’s group and others investigated the tandem [4 + 2]/[3 + 2] nitroalkene cycloaddition employing unactivated olefins or enol ethers as dienophiles and electron-deficient alkenes as 1,3

• -deficient C=C bond (Scheme 3). Thus, the approach of the enol ether to the β-nitro carbon was preferred by the less hindered Si face on the opposite side to the largest group. Secondary orbital and Coulombic interactions have been proposed to explain the endo approach of the enol ethers [9][33][41]. In the

Facile synthesis of functionalized tetrahydroquinolines via domino Povarov reactions of arylamines, methyl propiolate and aromatic aldehydes

• Jing Sun,
• Hong Gao,
• Qun Wu and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2012, 8, 1839–1843, doi:10.3762/bjoc.8.211

• dienophiles, vinyl enol ethers, vinyl enamides, vinyl sulfides, cyclopentadienes, indenes, alkynes and enamines have been mostly used in this method [12][13][14][15][16][17][18][19][20][21][22]. β-Enamino esters [23][24][25][26], which may be readily generated in situ by the addition of a primary amine to

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• -nucleophiles, which are listed in Figure 12 [61]. Figure 12 shows that the nucleophilicities N of the enamides 17 are comparable to those of silylated enol ethers, in between those of allylsilanes and enamines. Accordingly, we expected them to react readily with the iminium ions 3 at room temperature. However

Asymmetric organocatalytic decarboxylative Mannich reaction using β-keto acids: A new protocol for the synthesis of chiral β-amino ketones

• Chunhui Jiang,
• Fangrui Zhong and
• Yixin Lu

Beilstein J. Org. Chem. 2012, 8, 1279–1283, doi:10.3762/bjoc.8.144

• few decades [7]. Among them, the Mukaiyama–Mannich reaction performed with silyl enol ethers and sulfonyl aldimines, catalyzed by a chiral Lewis acid complex, is one of the most important synthetic methods [8][9][10][11][12][13]. Apparently, direct use of inactivated ketones as a donor would be of

Sonogashira–Hagihara reactions of halogenated glycals

• Dennis C. Koester and
• Daniel B. Werz

Beilstein J. Org. Chem. 2012, 8, 675–682, doi:10.3762/bjoc.8.75

• -Alkynylated glycals were obtained in very good yields whereas the alkynylation in position 2 gave poorer results. Chemoselective reduction of the triple bond in the resulting enyne system by the action of Raney-Ni furnished enol ethers, which could be readily refunctionalized. Methanol proved to be an

Facile isomerization of silyl enol ethers catalyzed by triflic imide and its application to one-pot isomerization–(2 + 2) cycloaddition

• Kazato Inanaga,
• Yu Ogawa,
• Yuuki Nagamoto,
• Akihiro Daigaku,
• Hidetoshi Tokuyama,
• Yoshiji Takemoto and
• Kiyosei Takasu

Beilstein J. Org. Chem. 2012, 8, 658–661, doi:10.3762/bjoc.8.73

• , Japan 10.3762/bjoc.8.73 Abstract A triflic imide (Tf2NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction

• sequence, Tf2NH catalyzes both of the reactions. Keywords: isomerization; one-pot reaction; organocatalysis; silyl enol ethers; triflic imide; Introduction Silyl enol ethers, which are isolable equivalents of metal enolates, are useful and important intermediates in synthetic chemistry [1][2][3]. They

• react as a good nucleophile for the introduction of a carbon skeleton or a functional group at the α-position of a carbonyl group under appropriate conditions. Although silyl enol ethers are easily prepared from the corresponding ketones, the regiochemical issue would arise in the case of asymmetric

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• (VIII) that participate in (4 + 2) annulations with polarized alkenes such as indoles, carbonyls, imines or silyl enol ethers [45]. Thus, different types of 6-membered carbocycles and heterocycles were prepared in good yields and notable regioselectivities. An example of these annulations, using indoles

Multicomponent reaction access to complex quinolines via oxidation of the Povarov adducts

• Esther Vicente-García,
• Rosario Ramón,
• Sara Preciado and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2011, 7, 980–987, doi:10.3762/bjoc.7.110

• through the Povarov MCR (the interaction of anilines, aldehydes and activated olefin inputs under acid catalysis) [4][5][6][7][8]. Interestingly, this process allows cyclic enol ethers and enamines to be used as electron-rich alkenes, leading to heterocycle-fused tetrahydroquinolines, usually as a mixture

• resulting from the reaction between 3-aminocoumarin, aldehydes and cyclic enol ethers have been oxidized with different types of reagents, such as bromide, palladium, DDQ, sodium periodate, manganese dioxide or CAN, but in all cases the main product was the elimination–oxidation compound [29]. Finally

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• enhancement. Recently, we further developed the gold(I)-catalyzed 7-exo-dig cyclization of acetylenic silyl enol ethers with L1 [57]. In this context, we expected that the use of L1 as a ligand in the gold-catalyzed intramolecular hydroamination of alkynes would enable the construction of nitrogen-containing

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• chirality transfer. Rüttinger et al. reported a gold-catalyzed synthetic route for the preparation of enynes (Scheme 4) [26]. The gold-catalyzed cyclization provided the corresponding exo-enol ethers 19 in moderate to high yield with complete regioselectivity. By contrast, Wilckens et al. reported the gold

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• . Upon coordination of the metal to the alkyne 59, the 1,4-dipole 61 can be formed from oxocarbenium 60. Carbonyl compounds and carbonyl derivatives, such as imines or silyl enol ethers, can also be used as dipolarophiles to generate bicyclic furans 62 in fairly good yields (Scheme 20, reaction 2