Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• Becquerel, 67087 Strasbourg, France 10.3762/bjoc.13.281 Abstract The acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicylic alkene using alcohol nucleophiles were investigated. Although this acid-catalyzed ring-opening reaction did not cleave the cyclopropane unit as planned, this

• ; alcohol nucleophiles; cyclopropanation; heterobicyclic compounds; ring-opening reactions; Introduction Heterobicyclic alkenes are useful templates to generate complex cyclic and acyclic systems [1][2]. 3-Aza-2-oxabicyclic alkenes are particularly interesting due to their asymmetric nature and the ability

• most cases, the starting material was completely consumed, the yields of these ring-opening reactions were only moderate (26–61%). This may be due to the decomposition or polymerization of the cyclopropanated 3-aza-2-oxabicyclic alkene under the reaction conditions. Through X-ray crystallography [20

Fluorinated cyclohexanes: Synthesis of amine building blocks of the all-cis 2,3,5,6-tetrafluorocyclohexylamine motif

• Tetiana Bykova,
• Nawaf Al-Maharik,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2017, 13, 728–733, doi:10.3762/bjoc.13.72

• building blocks for discovery chemistry programmes. The synthesis starts from a Birch reduction of benzonitrile, followed by an in situ methyl iodide quench. The resultant 2,5-cyclohexadiene was progressed via double epoxidations and then hydrofluorination ring opening reactions. The resultant fluorohydrin

Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

• Katrina Tait,
• Oday Alrifai,
• Rebecca Boutin,
• Jamie Haner and
• William Tam

Beilstein J. Org. Chem. 2016, 12, 2189–2196, doi:10.3762/bjoc.12.209

• Katrina Tait Oday Alrifai Rebecca Boutin Jamie Haner William Tam Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Guelph, Guelph, Ontario, N1G 2W1, Canada 10.3762/bjoc.12.209 Abstract Palladium-catalyzed ring-opening reactions of

• oxabenzonorbornadiene; palladium catalysis; ring-opening reactions; Introduction Heterobicyclic alkenes undergo important chemical transformations to provide highly substituted cyclic and acyclic systems [1][2]. Oxabicyclic alkene 1 specifically can undergo a variety of chemical transformations to generate highly

• conclusion, we have demonstrated the first examples of palladium-catalyzed type 2 ring-opening reactions of cyclopropanated oxabenzonorbornadienes with alcohols. The optimized conditions include PdCl2(CH3CN)2 with the alcohol nucleophile as the solvent at 60 °C or with toluene added at 90 °C to produce 2

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

• ] and the synthesis of carbamate-linked compounds using p-nitrophenyl carbonates, we herein report our results from nucleophilic ring opening reactions of DBU and DBN using p-nitrophenyl carbonates. Results and Discussion In the course of this study, we observed that in the absence of a nucleophile the

From N-vinylpyrrolidone anions to modified paraffin-like oligomers via double alkylation with 1,8-dibromooctane: access to covalent networks and oligomeric amines for dye attachment

• Daniela Obels,
• Melanie Lievenbrück and
• Helmut Ritter

Beilstein J. Org. Chem. 2016, 12, 1395–1400, doi:10.3762/bjoc.12.133

• thermo- [18] or/and pH [19] responsive polymers. Besides classical alkylation reactions, Reinecke et al. performed ring-opening reactions to insert functional groups and aromatic side chains [20][21]. Furthermore, they investigated the formation of homogeneous [22] and amphiphilic [23] N-VP networks

Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

• Michael Edmunds,
• Mohammed Abdul Raheem,
• Rebecca Boutin,
• Katrina Tait and
• William Tam

Beilstein J. Org. Chem. 2016, 12, 239–244, doi:10.3762/bjoc.12.25

• ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl2(PPh3)2, ZnCl2, Et3N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing

• ; oxabenzonorbornadiene; palladium catalysis; regioselectivity; ring-opening reactions; Introduction Palladium-catalyzed ring-opening reactions of 7-oxanorbornadiene with aryl iodides produce unsymmetrical, highly-substituted biphenyl derivatives making this reaction a very useful tool in organic synthesis [1][2][3][4

• materials [8]. Although there are several examples of palladium-catalyzed ring-opening reactions of oxabenzonorbornadiene (Scheme 1), there is relatively little literature regarding reactions of non-aromatic 7-oxanorbornadiene systems [9][10][11][12][13]. To our knowledge, there has only been one example of

Investigation on the reactivity of α-azidochalcones with carboxylic acids: Formation of α-amido-1,3-diketones and highly substituted 2-(trifluoromethyl)oxazoles

• Kandasamy Rajaguru,
• Arumugam Mariappan,
• Rajendran Suresh,
• Periasamy Manivannan and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2015, 11, 2021–2028, doi:10.3762/bjoc.11.219

• character of the C(2)–N double bond is higher than a normal imine (Figure 1) [10][26][27]. The generated substituted aziridines A2 may undergo further ring opening reactions. The α-azidochalcones 1 are suitable as precursors for the generation of 2H-azirines A1, though several other methods are available

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

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

• enormous strain and is therefore susceptible to ring-opening reactions with a variety of nucleophiles [3][4]. Such transformations lead to 1,2-heteroatom structures which are often found in pharmaceuticals and natural products. Yudin et al. described an electrochemical aziridination process where an

Regio- and stereoselective synthesis of new diaminocyclopentanols

• Evgeni A. Larin,
• Valeri S. Kochubei and
• Yuri M. Atroshchenko

Beilstein J. Org. Chem. 2014, 10, 2513–2520, doi:10.3762/bjoc.10.262

• case of 3d bearing two phenyl groups no epoxide ring opening was observed (Table 3, entries 3 and 4). Ring opening reactions for epoxides 6a,b Ring opening of epoxides 6a,b was investigated by the reaction with 9H-purin-6-amine (7d) and morpholine (7a) as the nucleophiles under the above conditions

• ring opening reactions of epoxides 3a,b, and this may be explained by the formation of 14a,b via the aziridimium intermediate 17. Based on earlier results [44], a mechanism of this transformation was hypothesized as shown in Scheme 2. The intermediate 17 is formed after the intramolecular rearrangement

• adduct due to the steric hindrance. Application of Lewis acid as a catalyst for the ring opening reactions of 6a,b provides an alternative mechanism that involves the formation of aziridinium intermediate 17. As a result, regioisomers 14a,b were obtained as the major products. Amine-based nucleophiles

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• excellent ee (up to 96%). In subsequent transformations, the β-lactone products underwent various ring opening reactions to provide very useful derivatives, such as 1,3-diketones and enol esters, with good diastereoselectivity. 2.12 Annulations through domino aza-MBH/Michael reactions Because

Multigramme synthesis and asymmetric dihydroxylation of a 4-fluorobut-2E-enoate

• James A. B. Laurenson,
• John A. Parkinson,
• Jonathan M. Percy,
• Giuseppe Rinaudo and
• Ricard Roig

Beilstein J. Org. Chem. 2013, 9, 2660–2668, doi:10.3762/bjoc.9.301

• . Nucleophilic ring opening reactions were performed on the crude cyclic sulfate mixtures because avoiding column chromatography at this stage led to a vast improvement in the overall yields. After ring opening, sulfate ester cleavage was achieved by stirring the concentrated residue in acid (20% H2SO4) and

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions

• Markus Leibeling and
• Daniel B. Werz

Beilstein J. Org. Chem. 2013, 9, 2194–2201, doi:10.3762/bjoc.9.258

• led to a total decomposition – most probably due to ring-opening reactions with bromosilanes [37]. Further, we investigated the influence of the amount of bromine on the reaction and concluded that stoichiometric quantities entirely fulfill the demands of the bromination (Table 1, entries 7 and 8

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

• Eietsu Hasegawa,
• Minami Tateyama,
• Ryosuke Nagumo,
• Eiji Tayama and
• Hajime Iwamoto

Beilstein J. Org. Chem. 2013, 9, 1397–1406, doi:10.3762/bjoc.9.156

• Eietsu Hasegawa Minami Tateyama Ryosuke Nagumo Eiji Tayama Hajime Iwamoto Department of Chemistry, Faculty of Science, Niigata University, Ikarashi-2 8050, Niigata 950-2181, Japan 10.3762/bjoc.9.156 Abstract Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol

• (II)-salt-promoted oxidative ring-opening reactions of selected bicyclic cyclopropanol derivatives. Results and Discussion In the initial phase of this effort, we examined the reaction of cyclopropyl silyl ether 1a (0.40 mmol) with copper(II) acetate, Cu(OAc)2 , (1.1 equiv) for 1 h at room temperature

• previous observation that ether is a better solvent than MeCN and DMF in Cu(BF4)2-promoted ring-opening reactions of cyclopropylsilyl ethers [39]. When CH2Cl2 is employed as solvent, formation of 2 becomes more efficient while the yield of 3 remains moderate (Table 1, entry 7). Although the effect of the

Exploration of an epoxidation–ring-opening strategy for the synthesis of lyconadin A and discovery of an unexpected Payne rearrangement

• Brad M. Loertscher,
• Yu Zhang and
• Steven L. Castle

Beilstein J. Org. Chem. 2013, 9, 1179–1184, doi:10.3762/bjoc.9.132

• [27]. Epoxide 17 was then subjected to ring-opening reactions with vinyl Grignard reagents in the presence of various copper salts. Surprisingly, only trace amounts of the desired product were detected, with recovered starting material and multiple byproducts typically comprising the majority of the

Preparation and ring-opening reactions of N-diphenylphosphinyl vinyl aziridines

• Ashley N. Jarvis,
• Andrew B. McLaren,
• Helen M. I. Osborn and
• Joseph Sweeney

Beilstein J. Org. Chem. 2013, 9, 852–859, doi:10.3762/bjoc.9.98

• -sulfonylation in aziridine chemistry, due to the ability of the group to activate the ring and the relative ease of its removal at the conclusion of a synthetic manipulation. We report here in full [30] the results of our studies on the synthesis of N-Dpp vinyl azidirines, and selected ring-opening reactions of

• using lower-order organocuprates. Previously, only 2-(2-carboxyethenyl)aziridines had been shown to undergo ring-opening reactions with a range of nucleophiles [41]. The π-allyl complexes derived from aziridines 1 and 2, formed in situ by using substoichiometric Pd(PPh3)4, underwent successful reaction

• mimic the high selectivity of the reaction with stannylcuprate. Complex mixtures of products were obtained from these reactions. Conclusion We have achieved the first syntheses and ring-opening reactions of N-Dpp vinyl aziridines. The ring-opening reactions are selective only when the nucleophilic co

Ring-opening reaction of 2,5-dioctyldithieno[2,3-b:3',2'-d]thiophene in the presence of aryllithium reagents

• Hao Zhong,
• Jianwu Shi,
• Jianxun Kang,
• Shaomin Wang,
• Xinming Liu and
• Hua Wang

Beilstein J. Org. Chem. 2013, 9, 767–774, doi:10.3762/bjoc.9.87

• between the structures of aryl groups and the efficiency of ring-opening reactions are discussed. Keywords: aryllithium reagents; 2'-arylthio-3,3'-bithiophene-2-carbaldehyde; dithieno[2,3-b:3',2'-d]thiophene; nucleophilicity; ring-opening reaction; Introduction Due to the promising optical and

• the synthesis of a series of symmetric substituted dithieno[2,3-b:3',2'-d]thiophenes and their ring-opening reactions in the presence of n-BuLi. The 3,3'-bithiophene-2-carbaldehydes were generated after quenching with an electrophile, i.e., dry DMF (Scheme 1) [5]. The uncommon ring opening of fused

• , high selectivity towards the ring opening was observed with n-BuLi when compared with other organolithium reagents. However, most of these ring-opening reactions mentioned above take place by using n-BuLi as the nucleophile to attack the sulfur atoms of thiophenes. Other organolithium reagents have

Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

• Holger F. Bettinger and
• Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

• ” conrotatory and disrotatory ring-opening reactions provide pathways for the isomerisation of 3 to 1,2-dihydro-1,2-azaborine. Similar to previous investigations of the ring opening of Dewar benzene (1), we find that the conrotatory pathway is lower in energy than the orbital-symmetry-forbidden disrotatory

4-Pyridylnitrene and 2-pyrazinylcarbene

• Curt Wentrup,
• Ales Reisinger and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 754–760, doi:10.3762/bjoc.9.85

• vacuum thermolysis (FVT) conditions cyanocyclopentadiene 6 is formed (Scheme 1). Several other carbene–nitrene rearrangements have been reported [3][4][5]. In addition to the ring expansion (1–2–3), two ring opening reactions have been investigated in recent years. Type I ring opening takes place in

Chemoenzymatic synthesis and biological evaluation of enantiomerically enriched 1-(β-hydroxypropyl)imidazolium- and triazolium-based ionic liquids

• Paweł Borowiecki,
• Małgorzata Milner-Krawczyk and
• Jan Plenkiewicz

Beilstein J. Org. Chem. 2013, 9, 516–525, doi:10.3762/bjoc.9.56

• oxide (1) under solvent-free conditions. The epoxide ring-opening reactions were carried for 24 h at elevated temperature (32 °C) and resulted in the formation of the appropriate alcohols (±)-3a and (±)-3b in high yields (Scheme 1). In the next step, the influence of crucial parameters in enzyme

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• phenylmagnesium reagent provided 3i whereas the reaction with a vinylmagnesium reagent gave 3j. The reaction mechanisms are shown in Scheme 25. They proposed that the carbon–carbon bond cleavage happened prior to the carbometalation reactions, which is different from other ring-opening reactions of cyclopropenes

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• , including homogeneous hydrogenation [1][2], C–H activation [3][4][5], asymmetric ring-opening reactions [6], and a variety of cycloisomerizations [7][8][9][10], and cycloadditions [11][12][13][14][15][16][17][18][19][20]. Traditionally these types of cycloisomerization and cycloaddition reactions are

Synthesis and ring openings of cinnamate-derived N-unfunctionalised aziridines

• Alan Armstrong and
• Alexandra Ferguson

Beilstein J. Org. Chem. 2012, 8, 1747–1752, doi:10.3762/bjoc.8.199

• -diphenylphosphinyl hydroxylamine. The resulting N-unfunctionalised aziridines are shown to be versatile synthetic building blocks that undergo highly selective ring-opening reactions with a wide range of nucleophiles. Keywords: amino acids; aziridination; organocatalysis; ring opening; stereoselectivity

Alkoxide-induced ring opening of bicyclic 2-vinylcyclobutanones: A convenient synthesis of 2-vinyl-substituted 3-cycloalkene-1-carboxylic acid esters

• Xiufang Ji,
• Zhiming Li,
• Quanrui Wang and
• Andreas Goeke

Beilstein J. Org. Chem. 2012, 8, 650–657, doi:10.3762/bjoc.8.72

• [18][19][20][21][22][23]. Ring-opening reactions of cyclobutanones are expected to be a valuable methodology for vicinal difunctionalization of double bonds. A prerequisite for this reaction to take place is the presence at C-2 of substituents capable of stabilizing the developing vicinal carbanion [6

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• steps similar to monocationic rearrangements, such as alkyl group shifts, Wagner–Meerwein shifts, hydride shifts, ring opening reactions, and other skeletal rearrangements. This review will describe these types of superelectrophilic reactions. Keywords: dication; rearrangement; superacid

• superelectrophiles are often densely charged species, they are also known for their tendencies to undergo rearrangement and charge migration reactions. These types of conversions will be examined in this review article, including ring opening reactions, carbon–carbon bond shifts, skeletal rearrangements, and charge

• migrations or hydride shifts. Simple Friedel–Crafts type reactions and cyclizations will not be covered. Review Ring opening reactions Several types of superelectrophiles are known to undergo ring opening reactions. The ring opening reaction step can be followed by the reaction with a nucleophile. For

Carbasugar analogues of galactofuranosides: α-O-linked derivatives

• Jens Frigell and
• Ian Cumpstey

Beilstein J. Org. Chem. 2010, 6, 1127–1131, doi:10.3762/bjoc.6.129

• or α-galacto carbapyranose 1,2-epoxides [16]. We considered the reactivity of a diastereomeric epoxide to the α-galacto carbafuranose epoxide 1, i.e., a β-talo epoxide 4, in nucleophilic ring-opening reactions. The same steric and electronic arguments on regioselectivity would predict attack at C1 in