ライフサイエンスコーパス: carbocation

1 ts as a hydride acceptor, forming a tertiary carbocation.

2 y via initial oxidation of C17 to an allylic carbocation.

3 s share an apparently identical intermediate carbocation.

4 contraction can give an alternative tertiary carbocation.

5 singlet carbene proportionally more than the carbocation.

6 mologated alkane and regenerate the original carbocation.

7 ion of the hydroperoxide to an epoxy allylic carbocation.

8 ansforming the putative sigma-alkylpalladium carbocation.

9 oxide pair, followed by deprotonation of the carbocation.

10 are successful, proceeding via an azetidine carbocation.

11 ornene systems proceeding via a nonclassical carbocation.

12 hed hypothesis of polar cyclization via a C1 carbocation.

13 le pathway involves a rare boryl-substituted carbocation.

14 dge, no other examples of open-shell singlet carbocations.

15 ms that undergo photoheterolysis to generate carbocations.

16 geometrical aspects present in the starting carbocations.

17 preferred for the biosynthetically relevant carbocations.

18 yl stabilization of solvolytically generated carbocations.

19 d Cotton effects and stability of the trityl carbocations.

20 ntiate the nonclassical structures for these carbocations.

21 xadienyl or 4-aryl-1-oxo-2,5-cyclohexadienyl carbocations.

22 s carbenes, carbon radicals, carbanions, and carbocations.

23 nucleophilic attack on intermediate tertiary carbocations.

24 e physical organic chemistry of carbenes and carbocations.

25 from computations on gas-phase reactivity of carbocations.

26 for the systematic enumeration of terpenoid carbocations.

27 The molecular structures of bowl-shaped carbocations 1 and 2 crystallized as salts with AlCl(4)(

28 f isomeric 3-trimethylsilyl-1-arylcyclobutyl carbocations, 10 and 11, where the cross-ring 3-trimethy

29 sole species observed is the C-7 protonated carbocation (15H+).

30 rgo heterolysis and afford the corresponding carbocations 3-C and 4-C.

31 exadien-1-one (1) leads to the generation of carbocation [3](+), capable of effecting hydride abstrac

32 The ortho-carbocation 4-o-C was detected by LFP in aqueous solutio

33 the barrier associated with the formation of carbocation 6 and its substituted analogues correlates w

34 involve rate-limiting formation of benzylic carbocations (6b and 8b), which have sufficient lifetime

35 The secondary ent-beyeran-16-yl carbocation (7) is a key branch point intermediate in me

36 the kinetic species and the ipso-protonated carbocation (9aH+) as the thermodynamic cation.

37 ethyl derivative (9) gave the C-7 protonated carbocation (9H+) as the kinetic species and the ipso-pr

38 ence for the involvement of a caryophyllenyl carbocation, a cyclobutyl intermediate, in the biosynthe

39 halides) or reactive intermediates (such as carbocations, alkyl radicals, or sigma-alkyl-metal speci

40 ar magnitude of the interactions between the carbocations along the reaction coordinate and the enzym

41 sigma(+) of classical 4-phenyl-X substituted carbocations also provides a means to accurately back-ca

42 gative charges on the bisphosphonate group ("carbocation analogue") at pH 7.5, was calculated.

43 nked in order of decreasing mole fraction of carbocation analogue.

44 ns and orientations of diverse substrate and carbocation analogues to other cyclases such as 5-epi-ar

45 hold this species in close proximity to the carbocation and cause preemptive termination through eli

46 d 1,2-butadiene (4) to form the 1-buten-2-yl carbocation and radical, respectively, and related affin

47 ) ether, which resulted from (-)-epicatechin carbocation and the methyl group of methanol.

48 rived hydrocarbon homologues and their ions (carbocations and carbanions) are discussed on the basis

49 , hydrocarbons, their derivatives, and ions (carbocations and carbanions)-with studied terrestrial ch

50 Generation and NMR studies of novel carbocations and carboxonium ions are reported from ster

51 logy enables the active-site localization of carbocations and demonstrates the presence of an active-

52 n contrast, the increased electron demand in carbocations and related electron-deficient TS- like str

53 ct from that of typical closed-shell singlet carbocations and, if appropriately stabilized, lead to o

54 through radical translocation, oxidation to carbocation, and nucleophilic trapping with H2O.

55 leophilic addition of C8' over N1' to the C3 carbocation, and the multitude of reactivity posed by th

56 ta-carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or homoallylic carbocation spe

57 e few known examples of ground-state triplet carbocations, and, to our knowledge, no other examples o

58 ere previously designed as mimics of several carbocations are actually better mimics of transition st

59 Carbocations are an interesting part of this group becau

60 These carbocations are connected by a transition structure.

61 Carbocations are crucial intermediates in many chemical

62 ite groups on the inherent reactivity of key carbocations are discussed, as are complex rearrangement

63 icals, reaction mechanisms, and nonclassical carbocations are discussed.

64 s and enzyme-promoted formation of secondary carbocations are discussed.

65 ver, studies of the vibrational structure of carbocations are not abundant, because their infrared sp

66 High yields of carbocations are obtained by photolyses of phosphonium s

67 First examples of stable carbocations are reported from several classes of thia-P

68 These carbocations are then essentially "frozen" in their orig

69 Carbocations are traditionally thought to be closed-shel

70 highly stabilized 3-trimethylsilylcyclobutyl carbocation as an intermediate.

71 the occurrence of benzynes and nonclassical carbocations as reaction intermediates, and he was instr

72 yclobutylethyl cation is also a nonclassical carbocation, as shown by calculations at the MP2/cc-pVTZ

73 eroxide group and consequent generation of a carbocation at C-4 has been suggested to account for ant

74 substituted alpha-methyl alpha-methoxybenzyl carbocations at 25 degrees C and I = 1.0 (KCl).

75 a first drift region and were fragmented to carbocations at 64 to 128 Td and 45 to 89 degrees C.

76 sformation probably involves an intermediary carbocation, based on observations with additional subst

77 compared to more traditional pericyclic and carbocation-based rearrangements.

78 y positioning their nitrogen in the proposed carbocation-binding site.

79 ermediate, which lacked stabilization of the carbocation by a pi-donor in the alpha-position.

80 The structures and energies of the carbocations C 4H 7 (+) and C 5H 9 (+) were calculated u

81 presence of AlCl(3) affords stable nonplanar carbocations C(20)H(10)CH(2)CH(2)Hal(+) (Hal = Cl (1) an

82 al geometry that is usually favored for this carbocation can be perturbed significantly toward the no

83 The carbocations can also be intercepted by simple nucleophi

84 surprising discovery that high-energy vinyl carbocations can be generated under strongly basic condi

85 to that seen with a broad range of aromatic carbocations/carbanions.

86 ing electron-deficient intermediates such as carbocations, carbodications, onium ions, etc.

87 The 11-step in-enzyme carbocation cascade is compared with the same reaction i

88 Mechanistic proposals for the carbocation cascade reaction leading to the tricyclic se

89 to occur during biosynthetic terpene-forming carbocation cascades are highlighted.

90 These natural products are formed via carbocation cascades that are directed in part by the co

91 h the vinyl ether C=C bond is polarized with carbocation character at the substituted carbon (C(int))

92 of distinct dimeric and trimeric fluorescent carbocations, characterized by their different photostab

93 ases generate terpenes employing diversified carbocation chemistry, including highly specific ring fo

94 The zeolite strongly stabilizes these carbocations compared to the gas phase, and the conversi

95 These "sobralene-like" carbocation conformations provide an exothermic pathway

96 A variety of long-lived carbocations containing the p-(pentafluorosulfanyl)pheny

97 from E(13-33)(+), i.e., from highly reactive carbocations, correlate excellently with the correspondi

98 sticity, and the significance of region 2 in carbocation cyclisation.

99 at a 1,4-alkyl shift proposed as part of the carbocation cyclization/rearrangement leading to ledol,

100 keletons of terpenoids are generated through carbocation-dependent cyclization cascades catalyzed by

101 er mimics of transition state structures for carbocation deprotonation.

102 ibed for the formation and rearrangements of carbocations derived from the biological methylation rea

103 eveloping an algorithm to enumerate possible carbocations derived from the farnesyl cation, the first

104 The open-shell singlet and triplet "carbocations" described here may have reactivity distinc

105 ion-stabilizing, whereas the 1,5-triazole is carbocation-destabilizing.

106 xaTPS8 from other TPSs leading to a distinct carbocation-driven reaction mechanism en route to the 5,

107 he various terpene skeletons by catalyzing a carbocation-driven reaction.

108 ith the formation of a relatively long-lived carbocation during rearrangement.

109 ints to an ionic intermediate (epoxy allylic carbocation) during catalysis.

110 termediacy of alkyl iodanes as stereodefined carbocation equivalents.

111 rranging in time to give the C-12 protonated carbocations exclusively (16aH+, 17aH+, and 18aH+).

112 r, these findings indicated that flavan-3-ol carbocations exist in extracts and are involved in the b

113 hat the reaction proceeds via a nonclassical carbocation followed by anti-1,2-migration.

114 roceeds through the intermediacy of benzylic carbocations followed by intramolecular cyclization and

115 oluene deprotonation and formation of benzyl carbocation, followed by nucleophilic attacks.

116 The thermodynamic barrier to carbocation formation increases by 14.5 kcal/mol as the

117 tion intermediate E that forms after allylic carbocation formation.

118 ine the activation enthalpy of the resulting carbocation formation.

119 ved in the formation of NDMA, for example, a carbocation formed from the decomposition of the methylf

120 s by controlling the in situ generation of a carbocation formed through the knot-promoted cleavage of

121 via parent B[c]Ph as well as in the benzylic carbocation formed via fjord-region epoxide ring opening

122 cyclization involving the interaction of the carbocation formed with a nitrogen atom.

123 sed on computed NPA charges for the benzylic carbocations formed by 1,2-epoxide (bay-region) and 5,6-

124 s that are essential for catalysis, with the carbocations formed on ionization being protected by Leu

125 bution modes in the regioisomeric protonated carbocations formed via parent B[c]Ph as well as in the

126 roceeding via the generation of a stabilized carbocation from an allylic oxonium intermediate and sub

127 quilibria, carbocations from diazotates, and carbocations from alkoxychlorocarbenes.

128 Photogeneration of carbocations from Ar(2)CH-PAr(3)(+)BF(4)(-) or -SbF(6)(-

129 on and derived carbenes, carbene equilibria, carbocations from diazotates, and carbocations from alko

130 hat the added flavan-3-ol attached to the C4 carbocations from procyanidins during depolymerization.

131 al oxidation is used to liberate high-energy carbocations from simple carboxylic acids.

132 angements concertedly yield the two stablest carbocations, G and L.

133 ed in the presence of the highly reactive C3 carbocation generated.

134 In addition, carbocations generated in situ by in-source fragmentatio

135 eta-silyl stabilization of benzocyclobutenyl carbocations generated in solution has been effectively

136 ive reaction pathways proceeding through syn carbocation-halide ion pairs and a higher order transiti

137 difficulty in eliciting facial control over carbocations has limited their utility as intermediates

138 on of carbenes, biradicals/radical pairs and carbocations have been also reported.

139 epicatechin or (+)-catechin with epicatechin carbocation in CsANRa transgenic flower extracts formed

140 or B2, demonstrating the role of flavan-3-ol carbocation in the formation of PAs.

141 SN1 catalytic mechanism and as mimics of the carbocation in the transition state of hUP1.

142 hydride transfer reactions from alcohols to carbocations in acetonitrile.

143 ounterions), and the generation of gas-phase carbocations in discharges usually produces several spec

144 The existence of epoxy allylic carbocations in fatty acid transformations is widely imp

145 d reactive control of intrinsically unstable carbocations in order to guide the resulting product dis

146 thway, as opposed to forming simple benzylic carbocations in the corresponding thermal route.

147 ocations were observed (as the sole or major carbocation) in all cases.

148 between cyanines and the new class of alkyne carbocations, in spite of their marked difference in BLA

149 or loss of a proton beta to the indanyl-type carbocations (indenes).

150 BTAC; alternative binding orientations of a carbocation intermediate could lead to the formation of

151 al modeling revealed a possible new tertiary carbocation intermediate E that forms after allylic carb

152 two steps: ring opening of the epoxide to a carbocation intermediate followed by migration of a MIDA

153 ed bases, facilitating TBA dehydration via a carbocation intermediate in an E1 mechanism; the calcula

154 ng interactions of BTAC may mimic those of a carbocation intermediate in catalysis.

155 hydroxylation at carbon C-8 of a postulated carbocation intermediate in the class II active site, fo

156 might be connected through a bridged 1,10,11-carbocation intermediate or transition state that resemb

157 omote ester dissociation and generation of a carbocation intermediate required for retinoid isomeriza

158 hment of the conformation of the macrocyclic carbocation intermediate required to produce the (Z)-C8,

159 We conclude that the unusual carbocation intermediate results from outer shell electr

160 roxyl radical TEMPO(.) as well as a reactive carbocation intermediate that can be intercepted by a wi

161 rated functional group is proposed to form a carbocation intermediate that facilitates hydride shift

162 on proceeds via an SN1 mechanism involving a carbocation intermediate that is common to the cis and t

163 and redox-active ester substrate to afford a carbocation intermediate that undergoes subsequent trapp

164 s well as the stabilization of the resulting carbocation intermediate through cation-pi interactions.

165 on the free energy for the formation of the carbocation intermediate, that is, the driving force Del

166 activity is dictated by the stability of the carbocation intermediate, the degree of charge transfer

167 s that while the reaction proceeds through a carbocation intermediate, this charged species likely re

168 activation of the C-C bond leads to a tight-carbocation intermediate, which is evident from the comp

169 via alternative rearrangement of the acidic carbocation intermediate.

170 e favors a mechanism that proceeds through a carbocation intermediate.

171 ignificantly stabilized gamma-trimethylsilyl carbocation intermediate.

172 p migration that involves the formation of a carbocation intermediate.

173 he axial attack of a solvent molecule on the carbocation intermediate.

174 diate suggested the involvement of a vinylic carbocation intermediate.

175 ed cyclononane from direct trapping of a bis carbocation intermediate.

176 tTPS19) resulted in premature termination of carbocation intermediates and accumulation of bi-, tri-,

177 suggested that previously proposed secondary carbocation intermediates are avoided.

178 ays due to altered modes of stabilization of carbocation intermediates as well as altered templates f

179 numerous skeletal types and deprotonates the carbocation intermediates at 14 different sites around r

180 Quantum chemical calculations on carbocation intermediates encountered during the convers

181 s involving formation of cyclized beta-silyl carbocation intermediates for electron-withdrawing group

182 we conclude that the formation of transient carbocation intermediates in terpene cyclization reactio

183 F198 appear to be well-oriented to stabilize carbocation intermediates in the cyclization cascade thr

184 are in close proximity to the substrate and carbocation intermediates of the enzymatic reaction.

185 ntified new conformations of the verticillyl carbocation intermediates on the taxadiene biosynthetic

186 nd ammonium or iminium analogues of bicyclic carbocation intermediates proposed for the natural cycli

187 The carbocation intermediates proposed in the literature do

188 ctivated with boronic acid catalysts to form carbocation intermediates that can be trapped in selecti

189 DFT calculations on the carbocation intermediates that connect the biosynthetic

190 e management and manipulation of high-energy carbocation intermediates that propagate the cyclization

191 new catalytic method is described to access carbocation intermediates via the mesolytic cleavage of

192 These reactive carbocation intermediates, which are generated with low

193 ole of W324 and H579 in the stabilization of carbocation intermediates.

194 plex reactions involving intricate series of carbocation intermediates.

195 formational preference of the donors and the carbocation intermediates.

196 yl cation is the hub of a complicated web of carbocations involved in the construction of diverse and

197 This stable carbocation is easily observed by NMR and optical spectr

198 ereochemistry of the attack of water on each carbocation is independent of whether the precursor is a

199 simple hydroxylation, suggesting that the C1 carbocation is not anchimerically stabilized by the 6,7-

200 This unusual carbocation is stabilized by a combination of partial ar

201 Each carbocation is stabilized by the 6-methoxy group and hel

202 est that 1,4-reduction of a putative indolyl carbocation is the dominant mechanistic pathway.

203 The formation of carbocations is reversible; after alkalization, the ions

204 one formation (by trapping of the beta-silyl carbocation) is also described.

205 abilized singlet carbene to gold-coordinated carbocation, is dictated by the carbene substituents and

206 3 arise from different conformations of the carbocation, its lifetime must be sufficiently long to p

207 d-type enzyme supports a perferryl-initiated carbocation mechanism for covalent heme formation in CYP

208 t C(11) of the all-trans substrate, or via a carbocation mechanism?

209 rmediate as the rate-determining step in the carbocation-mediated cis to trans epimerization process.

210 e, and model reactions for both radical- and carbocation-mediated migration.

211 at acidic pH where it undergoes concurrent, carbocation-mediated thermal rearrangement to cis-12-OH-

212 )-2x1 surface reveal that adducts form via a carbocation-mediated two-step mechanism.

213 ate-determining formation of a 2-substituted carbocation (naphthalenium ion) intermediate that for ci

214 e to short-lived and reactive trifluoroalkyl carbocations of the thiophene series.

215 From all of the in situ generated stable carbocations, only two exhibit intense Cotton effects in

216 ticipation or diastereoselective attack on a carbocation (or ion pair) rather than an S(N)i mechanism

217 ce both 11- and 13-cis isomers, supporting a carbocation (or radical cation) mechanism for isomerizat

218 oire of cation-pai interactions to include a carbocation-pai system resulting from the protonation of

219 itial boronate anion affords a more reactive carbocation paired with the non-nucleophilic hexafluoroa

220 cals to generate amidination products due to carbocation participation.

221 d dogma proposes that labile plant flavonoid carbocations (PFCs) play vital roles in the biosynthesis

222 ohexadienyl and phenoxyl radicals to yield a carbocation/phenoxide pair, followed by deprotonation of

223 geranyl diphosphate and terminating with the carbocation precursor to the final product cyclooctat-9-

224 amolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, pr

225 rom the previous proposal in the key step of carbocation propagation prior to the formation of the bi

226 itive probes to trace the formation of vinyl carbocations, provides exclusively the corresponding cyc

227 te are replaced by smaller residues enabling carbocation quenching by water.

228 inol instead of 11-cis-retinol, supporting a carbocation/radical cation mechanism of retinol isomeriz

229 ries of historically notable observations in carbocation reactions are discussed.

230 selectivity of the ion pair intermediates in carbocation reactions must allow for species lacking equ

231 drocarbons upon APCI, hydride abstraction by carbocation reagent ions, is not correct.

232 is,cis,cis-[4.5.7.5]oxafenestranes through a carbocation rearrangement cascade.

233 otonated cyclopropane (PCP(+)) structures in carbocation rearrangement is a decades-old topic that co

234 method to a trifurcating organic reaction, a carbocation rearrangement, and solvent-dependent Pummere

235 suggest that other transformations involving carbocation rearrangement, in both chemistry and biology

236 ich will be discussed, were (14)C tracing of carbocation rearrangements and benzyne formation, electr

237 ed engineering is hampered by highly dynamic carbocation rearrangements during catalysis.

238 Dynamics calculations are described for carbocation rearrangements involving product-forming pat

239 s work, electronic structure calculations on carbocation rearrangements leading to abietadienyl catio

240 verse carbon skeletons by catalyzing complex carbocation rearrangements, making them particularly cha

241 y principles for terpene-forming (and other) carbocation rearrangements.

242 and with n-hexane to form an isolable hexyl carbocation salt.

243 ubbed the "memory effect", since the initial carbocation seems to "remember" its origin when undergoi

244 t of charge migration, electron density at a carbocation site is found to increase with progression f

245 at, on initial diphosphate loss, the primary carbocation so formed bends down into the interior of th

246 lculations supported the intermediacy of the carbocation species and the transfer of hydride from tri

247 atalysts and that both an iron-nitrenoid and carbocation species may be reactive intermediates.

248 lues are due to the formation of an aromatic carbocation species upon protonation.

249 nyl carbocations, and allylic or homoallylic carbocation species via vinyldiazo compounds.

250 rone for adduct reorientation, via transient carbocation species, leading ultimately to formation of

251 3LYP/6-31G* computational studies indicate a carbocation stabilization energy of 16.6 kcal/mol.

252 t for aromaticity, consistent with cation-pi carbocation stabilization.

253 ion-state) dynamic effects, that is, how the carbocation structure changes in response to the distrib

254 In the case of potential nonclassical carbocations substituted with the p-(pentafluorosulfanyl

255 , concurrent hydrogen/alkyl group migration, carbocation substitution, benzylic conjugation) are also

256 tudies support the involvement of a tertiary carbocation that is coordinated to the iridium metal cen

257 leading to a conjugated and violet tertiary carbocation that returned immediately to the uncolored a

258 erts a strong electron-withdrawing effect on carbocations that is not offset by a resonance effect.

259 vates allylic alcohols to generate transient carbocations that react with in situ-generated chiral en

260 hermodynamically more stable C-12 protonated carbocations, the charge delocalization path is analogou

261 usual intramolecular 1,5-proton shift from a carbocation to a C-C double bond.

262 in S2 abstracts a proton from the lavandulyl carbocation to form the LPP product.

263 ution when relating computational studies on carbocations to solvolytic studies in common solvents.

264 anol to hydrocarbons, their derivatives, and carbocations together with a possible connection with me

265 -Prins cyclization and either elimination or carbocation trapping.

266 Quenching experiments on the carbocations under various conditions resulted in the fo

267 icient for the formation of alpha-diazo beta-carbocations (vinyldiazonium ions), vinyl carbocations,

268 of the oxatriquinane oxygen with a bridging carbocation was also examined.

269 he ring-expansion process, and the incipient carbocation was trapped with the alcohol residue generat

270 A set of heteroatom-substituted carbenes and carbocations was also examined.

271 for subsequent charge migration to 2 degrees carbocations were -49 to -58 kJ/mol.

272 charge delocalization modes in the resulting carbocations were also evaluated.

273 In several cases, the resulting carbocations were also studied by GIAO-DFT.

274 The experimentally observed carbocations were also studied computationally by GIAO-D

275 es for fragmentation of ROH(2)(+) to primary carbocations were calculated as 76 to 97 kJ/mol and enth

276 The (13)C NMR chemical shifts of the carbocations were calculated using the GIAO-CCSD(T) meth

277 Charge delocalization paths in the resulting carbocations were deduced based on the magnitude of Delt

278 The remarkably photostable trimeric carbocations were found to be formed predominantly near

279 A series of novel carbocations were generated by low-temperature protonati

280 A series of novel carbocations were generated from isomeric monoalkylated

281 Specifically, 18758 carbocations were generated, which we cluster into 74 cy

282 atives (16, 17, and 18), two ipso-protonated carbocations were initially formed (C-7/C-12), rearrangi

283 d 11-methyl), the C-7 or the C-12 protonated carbocations were observed (as the sole or major carboca

284 Charge delocalization modes in the resulting carbocations were probed.

285 dies, are consistent with the involvement of carbocations where the rear lobe of the gamma-Si-C bond

286 tivates branched alkanes to produce tertiary carbocations which are in equilibrium with olefins.

287 have as Bronsted bases and protonate to give carbocations which can be trapped by electron-rich arene

288 and efficient approach to form "carbophilic carbocations", which selectively react with carbon nucle

289 om methanol and InI3 to give the next-higher carbocation, which accepts a hydride from the starting a

290 uestration of the counteranion away from the carbocation, which allows full propagation of the cation

291 terpene biosynthesis is the protoaustinoid A carbocation, which can be diverted to either the berkele

292 3 undergoes dehydration to provide an allyl carbocation, which is trapped with water, thereby instal

293 This leads to a cyclopropane-stabilized carbocation, which triggers ring expansion and concomita

294 Carbocations, which are thus no longer transient interme

295 Replacing the carbocation with borane (preserving pi-accepting capabil

296 an effective mimic for the ent-beyeran-16-yl carbocation with potential applications as an active sit

297 ed strategy of computationally searching for carbocations with low-energy diradical states as a possi

298 a novel cascade of reactions of N-stabilized carbocations with pi-nucleophiles to create the tetracyc

299 triangulenes and helicenes are highly stable carbocations with planar and helical conformations respe

300 nstants for the reactions of phenolates with carbocations with the Gibbs energies for single-electron

301 nt 1,3-hydride shift would then relocate the carbocation within the transient macrocycle to expedite