Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• ]. Even so, industrial processes using CO2 as chemical feedstock are limited to the production of few large scale chemicals such as urea, methanol, salicylic acid as well as inorganic and organic carbonates [5]. Since CO2 is captured in huge amounts from the flue gases of fossil fuel combustion, it would

• CO2, active and selective catalysts for these reactions are scarce [9]. The reaction of CO2 with epoxides yields alternating polycarbonates, polyethercarbonates or cyclic carbonates (Scheme 1). The production of CO2-based polymers is considerably more challenging compared to the formation of cyclic

• carbonates. In consequence, industrially relevant catalysts, combined with efficient processes, have only recently emerged for the manufacture of alternating polycarbonates [10] and polyethercarbonates [11]. The respective research has mainly focussed on homogeneous zinc–alkoxide complexes [12] and chromium

Highly selective palladium–benzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions

• Antonio Monopoli,
• Pietro Cotugno,
• Carlo G. Zambonin,
• Francesco Ciminale and
• Angelo Nacci

Beilstein J. Org. Chem. 2015, 11, 994–999, doi:10.3762/bjoc.11.111

• -2-ylidene complex I was found to be a chemoselective catalyst for the Tsuji–Trost allylation of active methylene compounds carried out under neutral conditions and using carbonates as allylating agents. The proposed protocol consists in a simplified procedure adopting an in situ prepared catalyst

• from Pd2dba3 and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed. Keywords: active methylene compounds; allylic carbonates; Pd–benzothiazol-2-ylidene complex; Tsuji–Trost

• , as a precatalyst in the Tsuji–Trost allylation of active methylene compounds using carbonates as allylating agents (Scheme 1). Results and Discussion Allylic carbonates are suitable reagents for the Tsuji–Trost allylation as they enable to work under neutral conditions. The base required for

CO₂ Chemistry

• Thomas E. Müller and
• Walter Leitner

Beilstein J. Org. Chem. 2015, 11, 675–677, doi:10.3762/bjoc.11.76

• fixation of CO2, which can be applied in the synthesis of carboxylic acids [8]. Also highly interesting is the combination of enzymatic and photocatalytic approaches for activating CO2 [9]. Bifunctional catalyst systems are frequently needed and well-understood in the synthesis of cyclic carbonates [10

Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

• yields (up to 95%, Scheme 4). McBurney et al. prepared various N-heterocycles, using oxime carbonates as excellent precursors for the photoinduced generation of iminyl radicals, whereby at standard photolysis conditions, 3-substituted 6-methylphenanthridines were obtained in good to quantitative yields

• -halobenzyl)arylamines, oxime carbonates, isocyanobiphenyls, etc.). Phenanthridines are usually obtained within 2–3 reaction steps, by application of different radical initiators. An intriguing alternative is the radical generation by UV irradiation with or even without a photocatalyst. The major advantage of

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• temperatures and pressures to activate CO2 [2][3]. Efficient chemical incorporation of CO2 is limited to rather reactive substrates, like epoxides [4][5][6] and amines [7][8][9] to produce cyclic carbonates and carbamates, respectively, and even then, elevated reaction temperatures and/or complex catalyst

• systems are sometimes required. Urea is the main industrial product for which CO2 is applied as a C1 building block in a reaction with ammonia, still requiring pressures around 200 bar to drive the equilibrium to acceptable yields [10][11]. Another important end product of CO2 are inorganic carbonates

(CF₃CO)₂O/CF₃SO₃H-mediated synthesis of 1,3-diketones from carboxylic acids and aromatic ketones

• JungKeun Kim,
• Elvira Shokova,
• Victor Tafeenko and
• Vladimir Kovalev

Beilstein J. Org. Chem. 2014, 10, 2270–2278, doi:10.3762/bjoc.10.236

• , and acid anhydrides, dialkyl carbonates, methoxymagnesium methyl carbonate, N-acylimidazoles, acyl cyanides, and acylbenzotriazoles [4]. Though recently many modifications of this method have been proposed [5][6][7][8][9][10][11], it is noticeable that none of these techniques implements a direct

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

• phosphines possessing various chiral skeletons that have been used in asymmetric nucleophilic organocatalytic reactions, including annulations of allenes, alkynes, and Morita–Baylis–Hillman (MBH) acetates, carbonates, and ketenes with activated alkenes and imines, allylic substitutions of MBH acetates and

• carbonates, Michael additions, γ-umpolung additions, and acylations of alcohols. Keywords: asymmetric catalysis; chiral phosphine; nucleophilic; organocatalysis; organophosphorus; synthesis; Introduction During the past two decades, tertiary phosphine catalysts have been applied extensively in a wide range

• developments in nucleophilic chiral phosphine-catalyzed asymmetric reactions, including annulations of allenes, ketenes, alkynes, and Morita–Baylis–Hillman (MBH) carbonates with activated alkenes and imines, allylic substitution of MBH acetates and carbonates, Michael additions, γ-umpolung additions, and

Relay cross metathesis reactions of vinylphosphonates

• Raj K. Malla,
• Jeremy N. Ridenour and
• Christopher D. Spilling

Beilstein J. Org. Chem. 2014, 10, 1933–1941, doi:10.3762/bjoc.10.201

• phosphorus; relay; vinyl phosphonate; Introduction Over the last two decades, we have developed reactions for the formation of chiral non-racemic γ-substituted vinylphosphonates [1][2][3][4][5][6][7][8][9]. In particular, carbonate derivatives 1 (phosphono allylic carbonates) of allylic hydroxy phosphonates

• complete chirality transfer. Various carbon, nitrogen, and oxygen nucleophiles participate in the palladium-catalyzed substitution reactions of phosphono allylic carbonates 1. Vinylphosphonates formed in this way, for example 2a–e (Figure 1), have been used in the synthesis of the natural products

• relay step in the cross metathesis reaction mechanism. Natural products prepared using vinyl phosphonate intermediates. Palladium catalysed reaction of phosphono allylic carbonates. Approaches to the synthesis of centrolobine. Relay ring closing metathesis and relay cross metathesis. Cross metathesis

Comparing kinetic profiles between bifunctional and binary type of Zn(salen)-based catalysts for organic carbonate formation

• Carmen Martín and
• Arjan W. Kleij

Beilstein J. Org. Chem. 2014, 10, 1817–1825, doi:10.3762/bjoc.10.191

• employed as active catalysts for the formation of cyclic carbonates from epoxides and CO2. A series of kinetic experiments was carried out to obtain information about the mechanism for this process catalyzed by these complexes and in particular about the order-dependence in catalyst. A comparative analysis

• opposed to the binary catalyst that is connected with a first-order dependence on the catalyst concentration and a monometallic mechanism. Keywords: CO2 chemistry; cyclic carbonates; kinetic studies; salen complexes; zinc; Introduction Carbon dioxide may be regarded as an ideal, renewable carbon feed

• stock for the synthesis of organic compounds being also of interest in an industrial context [1][2][3][4][5]. This inexpensive, abundant and nontoxic source of carbon has been extensively used to convert epoxides into their respective cyclic carbonates [6][7][8][9] (Scheme 1), that find useful

Synthesis of 1-[bis(trifluoromethyl)phosphine]-1’-oxazolinylferrocene ligands and their application in regio- and enantioselective Pd-catalyzed allylic alkylation of monosubstituted allyl substrates

• Zeng-Wei Lai,
• Rong-Fei Yang,
• Ke-Yin Ye,
• Hongbin Sun and
• Shu-Li You

Beilstein J. Org. Chem. 2014, 10, 1261–1266, doi:10.3762/bjoc.10.126

• . Substrates bearing either an electron-donating group or electron-withdrawing group on the aromatic ring of the aryl allyl carbonates all proceeded smoothly in full conversion within 12 h. In all cases, the reactions gave excellent regioselectivity favoring the formation of the branched products in good to

• -substituted cinnamyl carbonates occurred smoothly to give excellent regio- and enantioselectivity (b/l: up to 99/1, up to 94% ee, entries 3, 11, 12, Table 2). In addition, heteroaryl allyl carbonates 4e and 4f also gave good regioselectivity with slightly lower enantioselectivity (entries 6 and 7, Table 2

• monosubstituted allyl carbonates. Further studies on the synthesis of 1-[bis(perfluoroalkyl)phosphine]-1’-oxazolinylferrocene ligands and their applications in asymmetric catalysis are ongoing in our lab. Representative ligands developed for the regio- and enantioselective Pd-catalyzed allylic alkylation

Continuous-flow Heck synthesis of 4-methoxybiphenyl and methyl 4-methoxycinnamate in supercritical carbon dioxide expanded solvent solutions

• Phei Li Lau,
• Ray W. K. Allen and
• Peter Styring

Beilstein J. Org. Chem. 2013, 9, 2886–2897, doi:10.3762/bjoc.9.325

• . Among them, tertiary amines such as triethylamine (Et3N), tributylamine (Bu3N) and alkali salts like carbonates, acetates or phosphates play crucial roles [7]. Solubility of the base and its basicity in the appropriate solvents are criteria that need to be considered. Traditionally, most Heck reactions

Modulating NHC catalysis with fluorine

• Yannick P. Rey and
• Ryan Gilmour

Beilstein J. Org. Chem. 2013, 9, 2812–2820, doi:10.3762/bjoc.9.316

• derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0

• substitution is evaluated in the NHC-catalysed, enantioselective Steglich rearrangement of oxazolyl carbonates 3 to C-carboxyazlactones 4 [29], recently reported by Smith and co-workers [30][31][32][33][34][35][36]. Fluorination sites were selected based on their proximity to the ring junction nitrogen of the

• (e.r. 62.5:37.5), although the reactions did not display the same sensitivity to changes in base (Table 2, entries 11 and 12). Conclusion In conclusion, the ability of fluorine to modulate the catalytic performance of N-heterocyclic carbenes in the Steglich rearrangement of oxazolyl carbonates has been

New developments in gold-catalyzed manipulation of inactivated alkenes

• Michel Chiarucci and
• Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

• normally activated equivalents, like halides, acetates, carbonates and phosphates are employed in metal-catalyzed Tsuji–Trost type alkylation [14][15]. 2 Formation of C–O bonds 2.1 Mechanistic considerations The addition of oxygen-based nucleophiles to C–C multiple bonds is an effective and atom-economical

• simple allylic alcohols as alkylating agents, in place of more activated analogues (i.e. halides, acetates, carbonates and phosphates) is highly desirable from a synthetic, environmental and economic point of view [61]. Late transition metal catalysts demonstrated efficiency in addressing the poor

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C₃-building block

• Volker M. Schmiedel,
• Stefano Stefani and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2013, 9, 2564–2569, doi:10.3762/bjoc.9.291

• and 1/2. In order to solve this problem and to obtain pure stereoisomers, the α-azidotetrahydrofuranols 9/10 were treated with benzyl chloroformate and converted into carbonates 16 and 17. This protection allowed the smooth separation of the diastereomers by simple flash chromatography, probably due

Asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with α-fluoro-β-keto esters

• Lin Yan,
• Zhiqiang Han,
• Bo Zhu,
• Caiyun Yang,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2013, 9, 1853–1857, doi:10.3762/bjoc.9.216

• and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 10.3762/bjoc.9.216 Abstract In the presence of a commercially available Cinchona alkaloid as catalyst, the asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates, with α-fluoro-β-keto esters as

• ). Keywords: allylic alkylation; asymmetric catalysis; fluorine; fluoro-β-keto esters; Morita–Baylis–Hillman carbonates; natural product; Introduction Fluorine is the most electronegative element in the periodic table, resulting in a highly polar C–F bond. This gives fluoro-organic compounds unique

• introduction of fluorine atoms in molecules has become one of the most exciting and intense research areas in the recent years. Lewis base-catalyzed asymmetric allylic alkylations (AAA) of Morita–Baylis–Hillman (MBH) adducts [5][6], such as acetates and carbonates, have become an attractive option to access

Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides

• Christian Dollendorf,
• Martin Hetzer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 1652–1662, doi:10.3762/bjoc.9.189

• considerably faster than the kinetics of other functionalities like esters and carbonates, whose degradation take days to weeks or even months inside the human body [29][30][31]. Dithiothreitol (DTT), tris(2-carboxyethyl)phosphine (TCEP) and glutathione tripeptide (γ-glutamyl-cysteinyl-glycine; GSH) are known

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• . Alcohol 63 was derivatized as the Boc carbonate, a reaction plagued by the formation of the carbonate arising from two molecules of 63. The ratio of Boc derivative to symmetrical carbonates is dependent on the acidity of the alcohol and not necessarily improved by increasing the stoichiometry of Boc2O [65

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• DFT computations, which gave insights into factors influencing the two cyclisation modes. Keywords: cyclisation; EPR spectroscopy; free radicals; heterocycles; oxime carbonates; Introduction Radical cyclisations onto aromatic acceptors take place readily, even though disruption of the 6π-electron

• carbocation, followed by proton loss. Kinetic or other data to help predict which mode would be favoured for a novel iminyl radical is essentially nonexistent. We discovered recently that oxime carbonates ArC(R)=N–OC(O)OR’ are clean and convenient precursors for iminyl as well as O-centred radicals [26][35

• radical intermediates to be directly monitored by EPR spectroscopy. We have now prepared a representative set of oxime carbonates with the aim of studying competition between ortho- and spiro-ring closures of the released iminyl radicals. Precursors 1a–f, 2a,b, 3 and 4, consist of O-ethoxycarbonyl

Preparation of mixed trialkyl alkylcarbonate derivatives of etidronic acid via an unusual route

• Petri A. Turhanen,
• Janne Weisell and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2012, 8, 2019–2024, doi:10.3762/bjoc.8.228

• scientific literature [19], while phosphorous (approximately 600 compounds) and phosphonic acid carbonates (approximately 20 compounds) are well known molecules. Since BPs are very hydrophilic, their bioavailabilities are very poor [20]. It would be a clear advantage if one could prepare more lipophilic and

• ), since in general OH and ONa groups react readily with chloroformates, forming the corresponding carbonates. However, the formed carbonate structure at the phosphorus end seems to be unstable since only rearranged products 3 could be isolated. Moreover, in the case of sterically more hindered isobutyl

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Impact of cyclodextrins on the behavior of amphiphilic ligands in aqueous organometallic catalysis

• Hervé Bricout,
• Estelle Léonard,
• Christophe Len,
• David Landy,
• Frédéric Hapiot and
• Eric Monflier

Beilstein J. Org. Chem. 2012, 8, 1479–1484, doi:10.3762/bjoc.8.167

• that the addition of randomly modified β-cyclodextrin (RAME-β-CD) in aqueous medium could have a beneficial impact on the catalytic performances of phosphane-based aggregates in the Pd-catalyzed cleavage of allyl carbonates (Tsuji–Trost reaction). The RAME-β-CD/phosphane supramolecular interactions

• carbonates (Tsuji–Trost reaction) and four amphiphilic phosphanes as aggregate-building blocks. The RAME-β-CD/phosphane interaction and its consequence on the catalytic results are discussed. Results and Discussion To expand the scope of the CD/amphiphilic phosphane combination in aqueous-phase

• ability of RAME-β-CD to supramolecularly recognize not only the phosphane but also the substrate. When mixed in excess with amphiphilic phosphanes, a proportion of the RAME-β-CD included phosphanes in their cavities, but the majority of RAME-β-CD interacted with allyl carbonates and acted as mass transfer

Organocatalytic asymmetric allylic amination of Morita–Baylis–Hillman carbonates of isatins

• Hang Zhang,
• Shan-Jun Zhang,
• Qing-Qing Zhou,
• Lin Dong and
• Ying-Chun Chen

Beilstein J. Org. Chem. 2012, 8, 1241–1245, doi:10.3762/bjoc.8.139

• investigation of a Lewis base catalyzed asymmetric allylic amination of Morita–Baylis–Hillman carbonates derived from isatins afforded an electrophilic pathway to access multifunctional oxindoles bearing a C3-quaternary stereocenter, provided with good to excellent enantioselectivity (up to 94% ee) and in high

• yields (up to 97%). Keywords: allylic amination; asymmetric organocatalysis; Morita–Baylis–Hillman carbonates; 2-oxindoles; quaternary chiral center; Introduction Chiral 3-amino-2-oxindoles are versatile and useful units for the preparation of natural products and drug candidates, such as the

• the other hand, the asymmetric addition to electrophilic imines of isatins is also an attractive pathway, and a variety of examples have been presented [16][17][18][19][20][21]. Recently, we have developed the asymmetric allylic alkylation reactions [22] with Morita–Baylis–Hillman (MBH) carbonates of

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

• cyclic carbonates 1a and 1b (Scheme 1) generate products derived from 1,3-diradical intermediates [14]. Interestingly, the photoinduced fragmentation reactions of nitrogen- and oxygen-containing functionalities have been studied intensively, whereas reports on photoextrusion reactions of sulfur

• because of its rapid secondary reaction. However, oxiranes have been observed as persistent intermediates under essentially identical conditions during photolysis of cyclic carbonates 1a and 1b, thus it is unlikely that they are formed to a significant extent in the photoreaction of 8. Similarly, we

• investigated the photochemistry of hydrobenzoin sulfite (9), which has been reported also to be a carbene precursor [16]. Because it has been shown in the case of cyclic carbonates that the application of milder reaction conditions enables the detection of reaction products that apparently decompose under

Chiral multifunctional thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of Morita–Baylis–Hillman carbonates with maleimides

• Hong-Ping Deng,
• De Wang,
• Yin Wei and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 1098–1104, doi:10.3762/bjoc.8.121

• (MBH) carbonates with maleimides, which can efficiently construct functionalized cyclopentenes bearing three contiguous stereocenters in moderate to excellent yields and excellent diastereo- and enantioselectivities. A plausible mechanism has been also proposed on the basis of control experiments and

• previous literature. Keywords: asymmetric [3 + 2] annulation; maleimides; Morita–Baylis–Hillman carbonates; multifunctional thiourea-phosphine; organocatalysis; Introduction Highly functionalized cyclopentene derivatives are important subunits in a variety of biologically active molecules and have

• ] have also developed asymmetric [3 + 2] annulations of allenoates to give the corresponding cyclopentene derivatives in good yields with excellent enantioselectivities [37]. On the other hand, some examples of phosphine-catalyzed [3 + 2] annulation of MBH carbonates with electron-deficient alkenes have

Aldol elaboration of 4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridin-4-ones, masked precursors to acylpyridones

• Raymond C. F. Jones,
• Abdul K. Choudhury,
• James N. Iley,
• Mark E. Light,
• Georgia Loizou and
• Terence A. Pillainayagam

Beilstein J. Org. Chem. 2012, 8, 308–312, doi:10.3762/bjoc.8.33

• four steps by the route shown in Scheme 3, involving palladium-catalysed decarboxylative ring opening of cyclic carbonates [23]. Thus the enolate of α-tetralone was added to propenal in an aldol addition (LDA, THF, −78 °C; 86%). The second step involved the reduction of the intermediate β-hydroxyketone