Direct C–H trifluoromethylation of di- and trisubstituted alkenes by photoredox catalysis

• Ren Tomita,
• Yusuke Yasu,
• Takashi Koike and
• Munetaka Akita

Beilstein J. Org. Chem. 2014, 10, 1099–1106, doi:10.3762/bjoc.10.108

• trifluoromethylating reagents (+CF3) can serve as more efficient CF3 radical sources under mild photocatalytic reaction conditions. In addition, the putative β-CF3 carbocation intermediate formed through SET photoredox processes is playing a key role in our reaction systems (vide infra). Trifluoromethylated alkenes

• the benzyl radical-type intermediate 3' in a regioselective manner. Subsequent one-electron-oxidation by highly oxidizing Ru species, [RuIII(bpy)3]3+, produces β-CF3 carbocation intermediate 3+. Finally, smooth elimination of the olefinic proton, which is made acidic by the strongly electron

• -withdrawing CF3 substituent, provides trifluoromethylated alkene 3. Preferential formation of one isomer in the reaction of unsymmetrical substrates is attributed to the population of the rotational conformers of the β-CF3 carbocation intermediate 3+. Our experimental result is consistent with the previous

Continuous flow nitration in miniaturized devices

• Amol A. Kulkarni

Beilstein J. Org. Chem. 2014, 10, 405–424, doi:10.3762/bjoc.10.38

• step is much slower – and hence rate-controlling – than the reverse of the second step due of the presence of water and the poor solubility of the aromatic species in the mineral acid medium. In the rate-controlling step the nitronium ion attacks the aromatic ring to give an intermediate carbocation

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

• delocalized carbocation B. The acetate radical could accept an electron from Ce2+ thereby forming an acetate anion, which could in turn attack the silyl moiety of allyltrimethylsilane leading to the formation of trimethylsilyl acetate and an allyl anion. The allyl anion could then attack at the anomeric

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

• products containing a dihydrooxepine moiety. In the case of occidenol (25, see Scheme 5), which has been isolated from the wood of Thuja koraiensis, farnesyl pyrophosphate (22) is supposed to undergo ring closure and the intermediate carbocation is trapped by hydroxide to give hedycaryol (23) [33

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

• approach to the synthesis of 1,2-dioxane rings is based on the intramolecular cyclization of hydroperoxides containing a C=C group. In the first step, the addition of a halonium ion to the double bond results in the formation of a carbocation, which is subjected to the intramolecular attack of the

Silica: An efficient catalyst for one-pot regioselective synthesis of dithioethers

• Samir Kundu,
• Babli Roy and
• Basudeb Basu

Beilstein J. Org. Chem. 2014, 10, 26–33, doi:10.3762/bjoc.10.5

• activate the double bond and subsequent assistance by the neighbouring sulfur atom coupled with the stability of the secondary carbocation lead to the Markovnikov addition resulting in the exclusive formation of 1,2-dithioether (Scheme 2, conditions A). On the other hand, the moist silica consisting of a

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

• , cationic [Au(I)] species exhibited comparable activity to TfOH at 85 °C (Table 1). This complementary behavior can be ascribed to different activation modes of the double bond. Computational investigations on the [H+]-catalyzed reaction predicted a transition state with significant carbocation character

• the key role of intramolecular hydrogen bond (H-bond) interactions for both reactivity and stereoselectivity [65]. Theoretical calculations and experimental evidences ruled out the SN1 reaction mechanism via allylic carbocation. Experiments with stereodefined hydroxy allylic alcohols revealed that the

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• of this intermediate and therefore facilitates the overall process. Finally, a ring-closing process through attack of the vinylgold species to the stabilized carbocation yields the cyclobutane system and regenerates the catalyst. In view of this mechanistic proposal, Mascareñas and López recently

Gold(I)-catalyzed 6-endo hydroxycyclization of 7-substituted-1,6-enynes

• Ana M. Sanjuán,
• Alberto Martínez,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2013, 9, 2242–2249, doi:10.3762/bjoc.9.263

• represented as two resonance structures highlighting both the carbocation or carbenoid nature of this intermediate (Scheme 2). Results and Discussion As established in Scheme 2, we were intrigued by the possibility that o-(alkynyl)-(3-methylbut-2-enyl)benzenes 1 could undergo a 6-endo-dig cyclization in the

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

• Peter A. Wade,
• Alma Pipic,
• Matthias Zeller and
• Panagiota Tsetsakos

Beilstein J. Org. Chem. 2013, 9, 2137–2146, doi:10.3762/bjoc.9.251

• , but products derived from carbocation rearrangement of the intermediate have been isolated. Houk et al. favor a concerted mechanism with no intervening energy minimum for cycloaddition based on calculational results [7][8][9]. The current results are in better agreement with the stepwise mechanism

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• decalin moiety has formed, two sigmatropic, stereospecific [1,2]-shifts of intermediate 170 provide the tertiary carbocation 171, which could be trapped by the phenolic alcohol to give stachyflin (156) [143]. In 2011, the first enantioselective total synthesis of (+)-stachyflin (156) via a Lewis acid

• the tertiary carbocation at the ring junction. This is then trapped by the phenol to give the pentacyclic compounds 180a and 180b. The former diastereoisomer could be converted to 180b via inversion of the secondary alcohol. Cleavage of the methyl ether and the 3,4-dimethoxybenzyl (3,4DMB) group of

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

• terminated by cyclopropylmethylsilane (Scheme 3, reaction 3), which may be explained by the participation of a carbocation that is stabilized by the adjacent cyclopropane ring in the bisected conformation where (CHOR)R′ is oriented anti to the cyclopropane [28][29][30]. Finally, Micalizio has described a

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

• )2 gives rise to tertiary carbocation 13 [51][52], which is then deprotonated to form enone 4. Studies of the effect of the counter ion on copper(II)-promoted reactions of 1b (Scheme 8) gave the results summarized in Table 2. While no reaction occurred when copper(II) acetylacetonate, Cu(acac)2, is

• fast oxidation of the more stable isomer 10 by stronger oxidants such as CuCl2 or Cu(OTf)2 occurs to give the stable tertiary carbocation 13, which is then captured by Cl− or MeCN. In order to explore the generality of the proposed counter-anion-dependent reactivity switch in the nature of copper(II

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

• István E. Markó and
• Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

• may indeed be operational in these cases. Protonation of diene 56 leads to the oxonium ion 57, which undergoes a 1,4-addition of another 56 unit, affording the new cation 58. At this stage, two different pathways can be followed. Either carbocation 58 can lose a proton, generating the observed triene

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• in good yields. Moreover, by simply moving into acetonitrile, they observed the selective oxygenation of phthalane to the corresponding phthalaldehyde in 80% yield [23]. In both cases the reaction proceeds via the formation of a carbocation intermediate (Scheme 7). The same research group also

Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides

• Pei Chui Too,
• Ya Lin Tnay and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2013, 9, 1217–1225, doi:10.3762/bjoc.9.138

• hydroperoxide deliver 1,4-diol 3a. In the absence of molecular O2 (under a N2 atmosphere, Table 1, entry 15), the resulting C-radical I is oxidized by the Cu(II) species to give carbocation VI [19], which is trapped by the intramolecular hydroxy group to give 4a. We next explored the substrate scope of the

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

• 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

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

• -dioxane product. The intermediate is of almost the same stability as the product, and two species were suggested to be in a state of equilibrium. While the geometry of TS1 appears to be forwarded to that of a carbocation intermediate, the cation disappeared through the enlargement of the water cluster

• ][11][12][13][14][15][16][17][18] to afford 1,3-dioxane, 1,3-diol and allylic alcohol, where the carbocation intermediate (X) is included (Scheme 5). In the second step, X is formed. From X, two routes, (i) and (ii), are possible. In the route (i), a water molecule is linked with the cation center

• ) bond is formed. After TS1(Me), not the carbonium ion but rather the butane-1,3-diol, diol(Me), is afforded. This result demonstrates that steps 1, 2 and 3 in Scheme 5 occur at the same time without intervention of the carbocation X. From diol(Me), two TSs were obtained. One is TS2(Me) leading to the

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

• -10-ol, reveal two mechanisms for caryolene formation: one involves a base-catalyzed deprotonation/reprotonation sequence and tertiary carbocation minimum, whereas the other (with a higher energy barrier) involves intramolecular proton transfer and the generation of a secondary carbocation minimum and

• a hydrogen-bridged minimum. Both mechanisms are predicted to involve concerted suprafacial/suprafacial [2 + 2] cycloadditions, whose asynchronicity allows them to avoid the constraints of orbital symmetry. Keywords: carbocation; cycloaddition; density functional theory; mechanism; reactive

• formation, applying the principles derived from previous theoretical studies on terpene-forming carbocation rearrangements [8]. In this mechanism, formation of the C1–C11 bond was expected to result in secondary carbocation B, in analogy to previously characterized pathways to sesquiterpenes containing 11

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

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

• Discussion Methyl cation affinities (MCA) The methyl cation (CH3+) is the smallest carbocation which is useful as a chemical probe for Lewis bases. The respective methyl cation affinity of a given Lewis base (LB) is obtained as the reaction enthalpy at 298.15 K and 1 bar pressure for the reaction shown in

Synthesis and antiviral activities of spacer-linked 1-thioglucuronide analogues of glycyrrhizin

• Christian Stanetty,
• Andrea Wolkerstorfer,
• Hassan Amer,
• Andreas Hofinger,
• Ulrich Jordis,
• Dirk Claßen-Houben and
• Paul Kosma

Beilstein J. Org. Chem. 2012, 8, 705–711, doi:10.3762/bjoc.8.79

• diphenylmethyl ester group with TFA/anisole (as carbocation scavenger), giving the monoacid derivatives 10 and 11 in 75% and 89% yield, respectively. Subsequent transesterification of 10 and 11 with methanolic NaOMe afforded the deacetylated methyl ester glucuronide derivatives 12 and 14, respectively, which

Efficient oxidation of oleanolic acid derivatives using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP): A convenient 2-step procedure towards 12-oxo-28-carboxylic acid derivatives

• Jorge A. R. Salvador,
• Vânia M. Moreira,
• Rui M. A. Pinto,
• Ana S. Leal and
• José A. Paixão

Beilstein J. Org. Chem. 2012, 8, 164–169, doi:10.3762/bjoc.8.17

• group, creating a tertiary carbocation at C-13. Then, a concerted stereoselective 1,2-migration of the 12β-H to the 13β-position with the rearrangement of the 12α-hydroxy group affords the final 12-oxo-28-carboxylic acid structure [18]. The molecular structure of compound 11, determined by single

Structural conditions required for the bridge lithiation and substitution of a basic calix[4]arene

• Conrad Fischer,
• Wilhelm Seichter and
• Edwin Weber

Beilstein J. Org. Chem. 2011, 7, 1602–1608, doi:10.3762/bjoc.7.188

• decade two main preparative routes for the methylene-bridge substitution of p-tert-butyltetramethoxycalix[4]arene have been established: A protocol described by Biali et al. yields a stabilized methylene carbocation through bromination that is ready for electrophilic substitution under SN1 conditions [3

Koch–Haaf reaction of adamantanols in an acid-tolerant hastelloy-made microreactor

• Takahide Fukuyama,
• Yu Mukai and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2011, 7, 1288–1293, doi:10.3762/bjoc.7.149

• organic molecules, and we also reported that Pd-catalyzed carbonylation [13] and radical carbonylation [16] could be successfully carried out in a continuous microflow system with higher efficiency than in a batch autoclave system. In this study, we focused on the carbonylation of carbocation