Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• synthesize stabilized chiral carbocations with chirality installed onto their backbones. Pioneering efforts along this line by Kagan, Sammakia, and Chen have shown that chiral catalysis with such chiral carbocations was indeed plausible to achieve stereocontrol (Scheme 1a). [14][15][16][17][18][19]. However

• with weakly coordinating metal-based phosphate anion. a) The reaction with 9,10-dimethylanthracene (3b). b) Gram-scale reaction of 3a and 4k, and transformation of cycloadduct 5k. Screening and optimization for the asymmetric catalyzed Diels–Alder reaction of anthracene by carbocations. Scope for the

• asymmetric catalyzed Diels–Alder reaction of anthracene (3a) with ketoesters 4 by carbocations. Supporting Information Supporting Information File 282: Experimental procedures and characterization data of all products, copies of 1H and 13C NMR, IR, HRMS, and HPLC spectra of all compounds. Acknowledgements

Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 789–794, doi:10.3762/bjoc.15.75

• enzymatic step [1][2][3]. With this approach, nature makes perfect use of the versatile chemistry of carbocations with its hydride or proton shifts and Wagner–Meerwein rearrangements leading to a large variety of possible structures. Among terpenoid natural products, achiral compounds are rarely found, but

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

• resulting α-allenic carbocations 24a–c (Scheme 14) [48]. As a complementary strategy, our group examined the [3,3]-sigmatropic rearrangement of cyanates derived from cyclopropenylcarbinols [53]. The allyl cyanate to isocyanate rearrangement displays many interesting features such as the possibility to

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• competes with the aliphatic side. It has been reported that the migratory tendency of substituents prefer those with a higher ability to accommodate the respective carbocations [46]. As anticipated, it was the phenyl moiety not the aliphatic moiety that moves from C(3) to N(2) to furnish the isolated

Correction: Dynamic behavior of rearranging carbocations – implications for terpene biosynthesis

• Stephanie R. Hare and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2017, 13, 1669–1669, doi:10.3762/bjoc.13.161

Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

• Takashi Nishikata,
• Alexander R. Abela,
• Shenlin Huang and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2016, 12, 1040–1064, doi:10.3762/bjoc.12.99

• with arylboronic [132][133][134], arylbismuth [135], and arylsilicon [136] reagents. Although carbocations react with arenes through electrophilic aromatic hydrogen substitution in a Friedel–Crafts reaction, the potential for metal cations to participate in similar chemistry has been far less widely

Dynamic behavior of rearranging carbocations – implications for terpene biosynthesis

• Stephanie R. Hare and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2016, 12, 377–390, doi:10.3762/bjoc.12.41

• Stephanie R. Hare Dean J. Tantillo Department of Chemistry, University of California–Davis, 1 Shields Avenue, Davis, CA 95616, USA 10.3762/bjoc.12.41 Abstract This review describes unexpected dynamical behaviors of rearranging carbocations and the modern computational methods used to elucidate

• rings that are transformed in only one or two enzyme-promoted reactions. These reactions involve generation of a carbocation by protonation or loss of a diphosphate group followed by cyclization, alkyl shift, hydride shift and/or proton transfer reactions to generate new, more complex, carbocations

• . Ultimately these carbocations are either trapped by a nucleophile (e.g., water, diphosphate) or deprotonated to form alkenes. The details of terpene-forming carbocation cyclization/rearrangement processes have been of interest for decades [1][2][3][4][5][6]. Although much has been learned, new observations

Smart molecules for imaging, sensing and health (SMITH)

• Bradley D. Smith

Beilstein J. Org. Chem. 2015, 11, 2540–2548, doi:10.3762/bjoc.11.274

• . David Kelly and worked on an NMR project on the structure of carbocations. I was lucky enough to stumble upon an unusual naphthalenium rearrangement process and I worked hard enough to earn co-authorship of a full paper in the Journal of the American Chemical Society [1]. As the year progressed I began

Investigation of the role of stereoelectronic effects in the conformation of piperidones by NMR spectroscopy and X-ray diffraction

• Cesar Garcias-Morales,
• David Ortegón-Reyna and
• Armando Ariza-Castolo

Beilstein J. Org. Chem. 2015, 11, 1973–1984, doi:10.3762/bjoc.11.213

• carbanions [13][14], carbocations [15][16][17][18], and free radicals [19][20][21] which has been explained by negative (nX→σ*C–Y) or positive hyperconjugation (σC–Y→π* or p). Hyperconjugation is commonly described as the interaction between electronic orbitals where one filled orbital (donor) interacts with

Attempts to prepare an all-carbon indigoid system

• Şeref Yildizhan,
• Henning Hopf and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 363–372, doi:10.3762/bjoc.11.42

• converted into cross-conjugated organic salts during the color-generating process. This is illustrated by indigo (1, Scheme 1) and its derivatives (e.g., Tyrian purple) and the triphenylmethane-derived carbocations. Starting from the generalized indigoid structure 2, the role of the heteroatoms X and Y can

Switching the reaction pathways of electrochemically generated β-haloalkoxysulfonium ions – synthesis of halohydrins and epoxides

• Akihiro Shimizu,
• Ryutaro Hayashi,
• Yosuke Ashikari,
• Toshiki Nokami and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2015, 11, 242–248, doi:10.3762/bjoc.11.27

• + or I+ and DMSO to unsymmetrically substituted olefins 2c and 2d regioselectively gave bromohydrins as single regioisomers (Table 2, entries 5–10). The regioselectivity of the products can be explained by the stability of carbocations (benzyl > secondary > primary). In the case of terminal alkene 2c

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

The Shono-type electroorganic oxidation of unfunctionalised amides. Carbon–carbon bond formation via electrogenerated N-acyliminium ions

• Alan M. Jones and
• Craig E. Banks

Beilstein J. Org. Chem. 2014, 10, 3056–3072, doi:10.3762/bjoc.10.323

• between anodically generated carbocations occurs by mass transfer diffusion across the liquid–liquid contact area. Therefore, one liquid can be oxidized and the other liquid containing the nucleophile can intercept the N-acyliminium ion formed in the microflow reactor (when the two sides of the channel

Automated solid-phase peptide synthesis to obtain therapeutic peptides

• Veronika Mäde,
• Sylvia Els-Heindl and
• Annette G. Beck-Sickinger

Beilstein J. Org. Chem. 2014, 10, 1197–1212, doi:10.3762/bjoc.10.118

• deprotected and conditions to remove both, side-chain protecting groups and the peptide from the resin, have to be used (Scheme 2) [20]. The last step of SPPS should be performed in the presence of scavengers to trap highly reactive carbocations that are formed during the cleavage procedure and that might

A new intermediate in the Prins reaction

• Shinichi Yamabe,
• Takeshi Fukuda and
• Shoko Yamazaki

Beilstein J. Org. Chem. 2013, 9, 476–485, doi:10.3762/bjoc.9.51

• , which leads to formation of the 1,3-diol and the subsequent allylic alcohol. In (ii), the second H2C=O is bound to the cation center, leading to formation of the 1,3-dioxane. While tertiary carbocations might intervene, the presence or absence of secondary ones would be critical in the aqueous media

• . This is because the water cluster has high nucleophilic strength and tends to make C–O bonds to form alcohols , overcoming the intervention of carbocations. In this respect, the mechanism depicted in Scheme 5 needs to be examined by the use of some alkenes theoretically. A variety of protic acids and

Caryolene-forming carbocation rearrangements

• Quynh Nhu N. Nguyen and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2013, 9, 323–331, doi:10.3762/bjoc.9.37

• encountered in the very first step involving carbocations. We were unable to locate a minimum for B in a productive conformation, despite the fact that alternative conformers of this secondary carbocation had been found to be involved in pathways to pentalenene and presilphiperfolanol [18][19][20][21][22

• represents the inherent reactivity of the carbocations involved in the formation of E, but how might the mechanism change if we allowed for an enzymatic base to be involved? Would the same unusual sequence of events associated with the intramolecular proton transfer persist? Would a lower energetic pathway

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

• are summarized under this title, whether they involve carbocations or carbanions, or “only” polarized intermediates, ionic reactions involving 2 and its derivatives have only been studied to a limited extent so far. And this situation does not change very much if we include the chemical behavior of

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

• -one (E = –6.75) [87] and, in particular, stabilized carbocations, which are generated in situ from the corresponding alcohols under weakly acidic conditions [14][88][89]. Suggestions for further promising electrophilic reaction partners in enamine activated reactions [90] can be derived from the

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• through charge delocalization [22]. Affinity numbers obtained for larger carbocations such as the benzhydryl cation may thus more closely mimic the steric and electronic properties of synthetically used carbon electrophiles. The corresponding benzhydryl cation affinity (BHCA) of a neutral Lewis base (LB

• towards different carbocations span an extraordinarily large energy range. In order to find out, whether different nucleophiles respond to changes in the electrophile in a systematically comparable manner, we have selected a small group of nucleophiles of different type for a direct comparison of affinity

• parameters N measured recently for these compounds and indicate that carbon basicities parallel the kinetics of base addition to carbocations for this class of compounds [47]. Guanidinyl pyridines such as 433 have, in contrast, surprisingly low ACA values around 230 kJ/mol. Structural changes in the

A practical microreactor for electrochemistry in flow

• Kevin Watts,
• William Gattrell and
• Thomas Wirth

Beilstein J. Org. Chem. 2011, 7, 1108–1114, doi:10.3762/bjoc.7.127

• the product at a flow rate of 10–15 µL·min−1 with a current of 0.6 mA. Yoshida reported a method of producing carbocations such as 1 in the absence of a suitable nucleophile (the "cation pool" method). This is an unconventional method because the ions generated are unstable and usually need to be

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

• was gathered which proved the reversible nature of the [3,3]-rearrangement in these cyclopropane probes. However, these transformations proved to be stereospecific in nature through gold-stabilized non-classical carbocations 100 and 100', even if the stereochemical information transfer to the product

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• gold-carbon order in the so-called organogold carbenoids. In the broad repertoire of gold-catalyzed organic transformations, gold-stabilized carbocations or, more often gold carbenes, can be found as intermediates in proposed mechanistic pathways, but the true nature of the organogold species had been

• a matter of debate [27]. Structural considerations: Gold-stabilized carbocations or gold carbenes? In 2008, Fürstner et al. took advantage of the ring-opening of 3,3-disubstituted cyclopropenes to generate organogold species and characterize them by NMR spectroscopy [16]. Whereas, 3,3

• = H), the reaction led to a complex mixture of products. The authors attributed these results to the formation of less stable carbocations at C3 (primary or secondary, respectively). Other examples of gold-catalyzed isomerization of cyclopropenes that involve a Friedel–Crafts cyclization have been

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

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

• this study, protolysis steps with alkanes often leads to β-scission reactions (cleavage of the alkane-based carbocations). This reaction path is not observed with superelectrophiles 70, 71, or 73, because these types of cleavage reactions would generate dicationic species with the cationic charges in

β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

• Jaya S. Kudavalli and
• Rory A. More O'Ferrall

Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118

• cis-and trans-1-chloro-2-hydroxy-1,2,3,4-tetrahydronaphthalene (1-chloro-2-tetralol, 4), which are similar in structure but lack a 3,4-double bond and yield carbocations which cannot undergo deprotonation to form aromatic products. Finally, to allow the influence of the β-hydroxy group on the rate of

Prins fluorination cyclisations: Preparation of 4-fluoro-pyran and -piperidine heterocycles

• Guillaume G. Launay,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2010, 6, No. 41, doi:10.3762/bjoc.6.41

• has been recently demonstrated, that if BF3·OEt2 is used in stoichiometric amounts then these reactions generate fluorinated products where the BF3·OEt2 contributes fluoride ion to quench the intermediate carbocations. In this study oxa- and aza-Prins reactions for the synthesis of 4-fluoro-pyrans and