ライフサイエンスコーパス: carbocation

1 le pathway involves a rare boryl-substituted carbocation.

2 s share an apparently identical intermediate carbocation.

3 contraction can give an alternative tertiary carbocation.

4 singlet carbene proportionally more than the carbocation.

5 mologated alkane and regenerate the original carbocation.

6 ion of the hydroperoxide to an epoxy allylic carbocation.

7 ansforming the putative sigma-alkylpalladium carbocation.

8 oxide pair, followed by deprotonation of the carbocation.

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

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

11 e physical organic chemistry of carbenes and carbocations.

12 geometrical aspects present in the starting carbocations.

13 preferred for the biosynthetically relevant carbocations.

14 from computations on gas-phase reactivity of carbocations.

15 yl stabilization of solvolytically generated carbocations.

16 for the systematic enumeration of terpenoid carbocations.

17 ntiate the nonclassical structures for these carbocations.

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

19 sm for the formation of the critical acylium carbocations.

20 rangements to the prenopsyl and norprenopsyl carbocations.

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

22 ms that undergo photoheterolysis to generate carbocations.

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

24 l fluoride (1-F) to form the 4-methoxybenzyl carbocation (1+).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

40 -quinone methide to give the 4-methoxybenzyl carbocation and of formaldehyde to give a simple oxocarb

41 bocation increases, and the distance between carbocation and phosphate anion decreases.

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

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

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

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

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

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

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

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

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

51 ermediates such as oxonium ylides, carbenes, carbocations, and free radicals are applicable.

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

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

54 These carbocations are connected by a transition structure.

55 Carbocations are crucial intermediates in many chemical

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

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

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

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

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

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

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

63 Carbocations are traditionally thought to be closed-shel

64 highly stabilized 3-trimethylsilylcyclobutyl carbocation as an intermediate.

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

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

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

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

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

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

71 ncreasing strain in the resulting bridgehead carbocation, but the range of rate constants was compres

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

73 er, followed by collapse of the intermediate carbocation by preferential attack of an external nucleo

74 s derived from capture of 1- and 2-adamantyl carbocations by the residual water in the ionic liquid.

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

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

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

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

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

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

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

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

83 ransition state analogues were produced with carbocation character and increased distance between the

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

85 As bond-breaking progresses, carbocation character builds on the ribosyl group, the d

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

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

88 the energy barriers for the reaction of each carbocation conformation with water.

89 he energy barrier for the inversion of these carbocation conformations must be large relative to the

90 ohydrin 5 yields a different distribution of carbocation conformations than that formed from the reac

91 hydrin exists for the interconversion of the carbocation conformations.

92 n catalyzes the interconversion of these two carbocation conformations.

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

94 The picture that emerges for the carbocation cyclization cascade is a delicate balance of

95 ed out to investigate the squalene-to-hopene carbocation cyclization mechanism in squalene-hopene cyc

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

97 In all alcohols studied, the carbocations decay on a somewhat slower time scale to yi

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

99 er mimics of transition state structures for carbocation deprotonation.

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

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

102 CCN(OTf) (29) all react in DMSO-d(6) to give carbocation-derived products.

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

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

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

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

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

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

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

110 uble bond in IPP or DMAPP to form a tertiary carbocation, followed by deprotonation.

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

112 ine the activation enthalpy of the resulting carbocation formation.

113 tion intermediate E that forms after allylic carbocation formation.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

131 erved for the reaction of the diphenylmethyl carbocation in methanol.

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

133 hydride transfer reactions from alcohols to carbocations in acetonitrile.

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

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

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

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

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

139 oup, the distance between the purine and the carbocation increases, and the distance between carbocat

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

141 posed to proceed through a verticillen-12-yl carbocation intermediate (8) that undergoes an 11 --> 7

142 ith PP(i) and aza analogues of the bisabolyl carbocation intermediate are reported.

143 e (PP(i)) and aza analogues of the bisabolyl carbocation intermediate are reported.

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

145 In this case, the carbocation intermediate derived from cyclization onto t

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

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

148 ns ratio of tetrols from the reaction of the carbocation intermediate from the hydrolysis of chlorohy

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

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

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

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

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

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

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

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

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

158 nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme.

159 22 suggests the involvement of a beta-silyl carbocation intermediate, and solvent isotope effect stu

160 does not appear to mimic that of the actual carbocation intermediate, suggesting that the avid inhib

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

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

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

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

165 olysis of each epoxide, which proceeds via a carbocation intermediate, yields the less stable cis dio

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

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

168 action removes H5beta from the final taxenyl carbocation intermediate.

169 he chromophore might occur through a retinyl carbocation intermediate.

170 ble with a proposed mechanism that invokes a carbocation intermediate.

171 ormed by the reaction of water with the C-10 carbocation intermediate.

172 via alternative rearrangement of the acidic carbocation intermediate.

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

174 ignificantly stabilized gamma-trimethylsilyl carbocation intermediate.

175 Substituent effect studies implicate carbocation intermediates (ion-pairs) that are captured

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 tic residues that shield the highly reactive carbocation intermediates from solvent and stabilize the

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

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

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

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

189 intermediates from solvent and stabilize the carbocation intermediates through cation-pi interactions

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

191 omplexes with aza analogues of substrate and carbocation intermediates, as well as complexes with pyr

192 plex reactions involving intricate series of carbocation intermediates.

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

194 orienting and stabilizing multiple reactive carbocation intermediates; the N-terminal domain has no

195 eroxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band

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

197 The carbocation is generated by anchimerically assisted regi

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

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

202 f an iron tricarbonyl stabilized pentadienyl carbocation is the triggering event of the cascade react

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

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

205 3 arise from different conformations of the carbocation, its lifetime must be sufficiently long to p

206 ater on the intermediate 2-hydroxy-1-indanyl carbocation leading to the less stable cis diol in this

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

208 these enzymes catalyze methyl transfer via a carbocation mechanism in which the bicarbonate ion acts

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

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

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

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

213 )-2x1 surface reveal that adducts form via a carbocation-mediated two-step mechanism.

214 The putative bisabolyl carbocation mimic, R-azabisabolene, binds in a conformat

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

216 This contrasts with the free i-Pr(+) carbocation observed when the anion is less coordinating

217 fer from the C(alpha)-H bond to an incipient carbocation on C(delta)(') or C(epsilon)(') via a five-

218 yrophosphate indicates an important role for carbocation/OPP anion stabilization of the secondary san

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

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

221 acid to protonate the substrate, yielding a carbocation/oxocarbonium ion that is then rapidly hydrat

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

223 cals to generate amidination products due to carbocation participation.

224 isingly, these processes that are typical of carbocations persist in hydrocarbon solvents such as pen

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

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

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

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

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

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

231 In methanol, the quantum yield of carbocations reaches a maximum value of 0.18 approximate

232 y be side chain protonated and are thus poor carbocation reactive intermediate analogues.

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

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

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

236 l trifluoroacetate all give products derived carbocation rearrangements (kDelta processes).

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

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

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

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

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

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

243 ployed which made classical and nonclassical carbocation S(N)1 reaction pathways unlikely.

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

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

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

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

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

249 alent heme attachment most likely involves a carbocation species located on the porphyrin.

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

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

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

253 3LYP/6-31G* computational studies indicate a carbocation stabilization energy of 16.6 kcal/mol.

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

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

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

257 that hydrolysis proceeds via an intermediate carbocation that has a sufficient lifetime to be trapped

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

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

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

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

262 rences in sterol structure, concerted versus carbocation; the kinetic mechanism remains the same duri

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

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

265 tion of solvent water to the 4-hydroxybenzyl carbocation to give pK(R) = -9.6 as the Lewis acidity co

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

267 -Prins cyclization and either elimination or carbocation trapping.

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

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

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

271 The charge delocalization in these carbocations was probed by (13)C NMR chemical shifts and

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

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

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

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

279 A series of novel carbocations were generated from isomeric monoalkylated

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

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

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

283 Charge delocalization modes in the resulting carbocations were probed.

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

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

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

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

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

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

290 3 undergoes dehydration to provide an allyl carbocation, which is trapped with water, thereby instal

291 Carbocations, which are thus no longer transient interme

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

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

294 is of diol epoxide 1, which hydrolyzes via a carbocation with the same connectivity as that formed in

295 (N)1 mechanism involving a relatively stable carbocation with two possible conformations.

296 vis) spectra of benzenium adducts of acylium carbocations with hexamethylbenzene can be measured and

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