Reactive intermediates – carbocations
This series covers a range of interesting organic and biological reactions involving generation of carbocations. Of particular interest are mechanisms of carbocation rearrangements, evidence of non-statistical dynamic effects playing a role in product formation for mechanisms involving carbocation intermediates, and applications in synthesis.
- Letter
- Published 27 Mar 2019
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Figure 1: Structures of achiral terpenes: (E)-β-farnesene (1), α-humulene (2), 1,8-cineol (3) and sodorifen (4...
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Figure 2: A) Total ion chromatogram of a hexane extract from the incubation of FPP with BbS and B) EI mass sp...
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Scheme 1: Cyclisation mechanism to 5 involving either the intermediates (R)-NPP and (S)-A (path A) or (S)-NPP...
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Figure 3: Total ion chromatograms of hexane extracts from incubation experiments with BbS and A) (R)-NPP, B) (...
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Figure 4: Hypothetical BbS active site comparable conformational folds of A) FPP, B) (R)- and C) (S)-NPP expl...
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- Published 14 Jun 2019
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Scheme 1: Asymmetric carbocation catalysis.
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Scheme 2: Synthesis of new carbocation catalysts with weakly coordinating metal-based phosphate anion.
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Figure 1: Dissociation of latent carbocation by the use of Lewis acids. a) UV–vis absorption spectra of TP (0...
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Scheme 3: a) The reaction with 9,10-dimethylanthracene (3b). b) Gram-scale reaction of 3a and 4k, and transfo...
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- Published 03 Jul 2019
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Scheme 1: Examples of 2e-3c and 2e-4c bonded structures.
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Figure 1: CCSD(T)/cc-pVTZ (MP2/cc-pVTZ) optimized structures and relative energies [in kcal/mol] of 1–4.
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Figure 2: (a) Total electron density, (b) HOMO and (c) LUMO of the dication 1; coefficients are calculated at...
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- Published 08 Jul 2019
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Figure 1: Allenes 1a–j used in this study.
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Scheme 1: Transformations of allene 1g in TfOH leading to the formation of cations E1, E2 and E4 including se...
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Figure 2: 31P NMR monitoring of the progress of transformation of E1 into E2 and E4 in TfOH at room temperatu...
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Scheme 2: Results of the hydrolysis of cations A–H.
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Scheme 3: Preparation of amides 6a,b from cations A, B, and F–H.
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Scheme 4: Large-scale one-pot solvent-free synthesis of amides 6a,b from the corresponding propargylic alcoho...
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Scheme 5: AlCl3-promoted hydroarylation of allene 1b by benzene leading to alkene Z-11n.
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Scheme 6: Reaction of allene 1a with benzene under the action of AlCl3 followed by quenching of the reaction ...
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Scheme 7: Multigram-scale one-pot synthesis of indane 12d from 2-methylbut-3-yn-2-ol.
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Figure 3: NMR spectra of starting allene 1a (black) and its complex with 1 equivalent of AlCl3 13 (red) in CD2...
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Scheme 8: 1H, 13C, and 31P NMR monitoring of AlCl3-promoted reactions of allene 1a leading to compounds E-14 ...
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Scheme 9: Plausible reaction mechanism A for the formation of compounds 9, 10, 11, 12 from aillene 1a involvi...
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Scheme 10: Plausible reaction mechanism B of formation of compounds 11, 12 from allene 1a involving HCl–AlCl3 ...
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Figure 4: Visualization of LUMO, only positive values are shown, isosurface value 0.043: (a) species 16, (b) ...
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- Published 09 Jul 2019
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Scheme 1: Superelectrophilic species.
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Scheme 2: Synthesis of diol substrate 9.
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Scheme 3: Isolated yields of products from diol 9.
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Scheme 4: Proposed mechanisms leading to products 10 and 11.
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Scheme 5: Products and relative yields from the reaction of alcohol 18 with CF3SO3H and C6H6 [12].
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Scheme 6: Comparison of superelectrophilic carbocations (3–5 and 14) and their chemistry.
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Scheme 7: DFT calculated relative energies of pentacations 16 and 21 [14].
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- Published 11 Jul 2019
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Scheme 1: Oxidation of alkanes with RuO4.
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Scheme 2: Mechanisms for RuO4 oxidation of alkanes.
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Scheme 3: Oxidation of saturated five-membered (hetero)cyclic compounds.
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Scheme 4: Rate-limiting step for the oxidation of cyclopentane (R1), tetrahydrofuran (R2) and tetrahydrothiop...
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Figure 1: Optimized (B3LYP-d3bj/Def2SVP/cpcm=MeCN) geometries of transition structures corresponding to the o...
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Figure 2: ELF analysis for the oxidation of cyclopentane (R1). Left: evolution of the electron population alo...
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Figure 3: ELF analysis for the oxidation of tetrahydrofuran (R2, A) and tetrahydrothiophene (R3, B). Left: ev...
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Figure 4: ELF assignment of electrons to the Ru environment. C(Ru) corresponds to a monosynaptic core basin a...
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Scheme 5: Rate-limiting step for the oxidation of N-methyl- and N-benzylpyrrolidines R4 and R5, respectively.
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Figure 5: Energy profile for the oxidation of R4 and R5. Relative energies, calculated at the B3LYP-d3bj/Def2...
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Figure 6: Optimized (B3LYP-d3bj/Def2SVP/cpcm=water) transition structures for the oxidation of R4 and R5.
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- Letter
- Published 12 Jul 2019
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Figure 1: Proposed mechanism of the asymmetric aza-Piancatelli reaction.
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Scheme 1: Asymmetric aza-Piancatelli rearrangement with a range of substituted anilines. *To simplify the pur...
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Scheme 2: Asymmetric aza-Piancatelli rearrangement with a range of substituted furylcarbinols. *To simplify t...
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- Published 24 Jul 2019
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Scheme 1: Solvolyses of cyclopropylcarbinyl and cyclobutyl substrates.
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Scheme 2: The cyclopropylcarbinyl–cyclobutyl–homoallyl cation manifold.
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Figure 1: Electron-deficient carbocations.
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Scheme 3: Solvolyses of γ-trimethylsilylcyclobutyl substrates.
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Figure 2: Substrates of interest.
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Scheme 4: Synthesis of mesylates 19 and 20.
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Scheme 5: Reaction of mesylate 19 in CD3CO2D.
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Scheme 6: Reaction of mesylate 20 in CD3CO2D.
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Figure 3: M062X/6-311+G** calculated structures and relative energies of cations 24, 27, and transition state ...
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Scheme 7: Synthesis of mesylates 31 and 32.
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Scheme 8: Reaction of mesylate 31 in CD3CO2D.
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Scheme 9: Reaction of mesylate 32 in CD3CO2D.
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Scheme 10: Reaction of trifluoroacetate 48 in CD3CO2D.
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Scheme 11: Bicyclobutane formation from a γ-trimethylsilyl cation.
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Scheme 12: Formation of triflates 60 and 61.
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Scheme 13: Formation of triflates 67, 68, and 69.
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Scheme 14: Reactions of substrates with electron-withdrawing groups in CD3CO2D.
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Figure 4: γ-Trimethylsilyl cations.
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Scheme 15: Bicyclobutane formation from mesylate 76 in CH3CO2H.
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Scheme 16: Reactions of triflates 60 and 67 in CD3CO2D.
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- Letter
- Published 07 Aug 2019
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Scheme 1: The regio- and stereoselectivity in quiannulatene and sesterfisherol biosynthesis are determined by...
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Scheme 2: Reaction mechanism of quiannulatene biosynthesis. GFPP: geranylfarnesyl diphosphate, IM: intermedia...
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Scheme 3: Reaction mechanisms of sesterfisherol biosynthesis. Sesterfisherol is formed by the hydration of IM...
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Figure 1: Energy diagram and heat map analysis of 5/12/5 tricycle formation (A) IM1–IM4 in quiannulatene bios...
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Figure 2: Energy diagram and heat map analysis of conformational change and hydrogen shift (A) IM4–IM6e in qu...
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Figure 3: Energy diagram and heat map analysis of ring rearrangement (A) IM6e–IM11 in quiannulatene biosynthe...
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- Published 02 Sep 2019
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Figure 1: Atorvastatin calcium trihydrate (1) and previously published decomposition products arising from tr...
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Scheme 1: Formation of novel artefacts 6 and 7 under extremely strong acidic conditions.
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Figure 2: Top: Molecular structure of artefact 6. Shown here is the molecular structure of one of three indep...
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Figure 3: Separation of atorvastatin (1; retention time: 5.8 min) from the four decomposition products 2 (ret...
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Scheme 2: Proposed mechanism for the formation of desamidated product 7.
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Scheme 3: Proposed mechanism for the formation of bridged product 6 under cyclization, isopropyl migration an...
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- Published 06 Nov 2019
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Scheme 1: Acid-catalyzed rearrangements of arenes.
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Scheme 2: Rearrangement of quaterphenyl isomers by phenyl shifts.
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Scheme 3: Synthesis of quaterphenyl isomers.
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Scheme 4: Rearrangement of quaterphenyl isomers via (a) 1,2-phenyl shift and (b) 1,2-biphenyl shift.
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Figure 1: Pathways for terminal 1,2-phenyl shifts in quaterphenyl isomers calculated with IEFPCM(DCE)/B3LYP/6...
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Figure 2: Pathways for 1,2-biphenyl shifts in quaterphenyl isomers calculated with IEFPCM(DCE)/B3LYP/6-31+G(d...
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- Published 08 Jan 2020
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Scheme 1: Mechanism for formation of cyclooctat-9-en-7-ol, published similarly in [42].
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Figure 1: Computed electronic energy profiles (kcal/mol) for the CotB2 cyclase mechanism. The calculations us...
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Figure 2: Intermediates A–I in the active site model. Interactions are marked by dashed orange lines, the int...
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Figure 3: TS structures TS_A_B–TS_G/H_I in the active site model. Interactions are marked by dashed orange li...
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Figure 4: Comparison between gas phase and active site model conformations. A) Intermediate D. B) Intermediat...
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