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Search for "NICS" in Full Text gives 10 result(s) in Beilstein Journal of Organic Chemistry.
Biphenylene-containing polycyclic conjugated compounds
- Cagatay Dengiz
Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141
- structural designs. NICS (nucleus independent chemical shift) analysis revealed that the linear structures within the series exhibited reduced antiaromaticity in the CBD ring compared to other structural arrangements. By employing a methoxy group on the oxonorbornene, the methyl ether moiety can be removed
Graphical Abstract
Figure 1: The correlation between stability and Clar's rule in acenes.
Scheme 1: General synthetic strategies to access the biphenylene core 1.
Figure 2: [N]Phenylenes 7–12 with different topologies.
Scheme 2: Synthesis of POAs 15a and 15b via reactions of BBD 13 and bis(cyanomethyl) compounds 14a and 14b.
Scheme 3: Synthesis of benzo[b]biphenylene (18).
Scheme 4: Synthesis of benzobiphenylene 18 and POA 21.
Scheme 5: Synthesis of symmetric POAs 25a and 25b.
Scheme 6: Synthesis of POA 29 via palladium-catalyzed annulation/aromatization reaction.
Scheme 7: Synthesis of bisphenylene-containing structures 34a–c.
Scheme 8: Synthesis of curved PAH 38 via Pd-catalyzed annulation and Ir-catalyzed cycloaddition reactions.
Scheme 9: Synthesis of [3]naphthylenes.
Scheme 10: Sequential Pd-catalyzed annulation reactions.
Scheme 11: Synthesis of biphenylene-containing unsymmetrical azaacenes 54a–c.
Scheme 12: Synthesis of biphenylene containing symmetrical azaacenes 58a,b.
Scheme 13: Synthesis of azaacene analogues 62–64.
Scheme 14: Synthesis of POA-type structure 69.
Scheme 15: Synthesis of boron-doped POA 73.
Scheme 16: Synthesis of “v”- and “z”-shaped B-POAs 77 and 78.
Scheme 17: Synthesis of boron-doped extended POA 84.
Scheme 18: Ag(111) surface-catalyzed synthesis of POA 87.
Scheme 19: Au(100) and Au(111) surface-catalyzed synthesis of POA 91.
Scheme 20: Au(111) on-surface synthesis of POA 87.
Unprecedented synthesis of a 14-membered hexaazamacrocycle
- Anastasia A. Fesenko and
- Anatoly D. Shutalev
Beilstein J. Org. Chem. 2023, 19, 1728–1740, doi:10.3762/bjoc.19.126
- deviation of 0.054 Å from the mean-square plane. The nuclear-independent chemical shift (NICS) [48][49][50] values of 5 in its optimized conformation were used as a magnetic criterion of aromaticity. The NICS(0) value for the macrocyclic ring (+2.23 ppm in DMSO), calculated at the HF/6-31+G(d) level, shows
- its somewhat anti-aromatic character. Obvious aromaticity of the pyrazole rings is confirmed by the NICS(0) values of −12.64 ppm. Macrocycle 5 has various reactive centers, including two amidrazone fragments with primary amino groups, which makes it possible to modify it in many ways [51][52][53][54
- macrocyclic core [NICS(0) = +2.23 ppm calculated at the HF/6-31+G(d) level]. Since numerous heterocyclic and carbocyclic analogs of 3-amino-1-methyl-1H-pyrazole-4-carbonitrile (3), which is the starting material in the synthesis of macrocycle 5, are readily available, we believe that our results will be
Graphical Abstract
Scheme 1: Synthesis of the key intermediate of the macrocycle preparation, 3-[(ethoxymethylene)amino]-1-methy...
Scheme 2: Synthesis of macrocycle 5 by the reaction of imidate 4 with hydrazine hydrate.
Scheme 3: Plausible pathway for the transformation of imidate 4 into macrocycle 5.
Scheme 4: Synthesis of pyrazolopyrimidine 8 by the reaction of imidate 4 with hydrazine hydrate.
Scheme 5: Synthesis of macrocycle 5 by the dimerization of pyrazolopyrimidine 8.
Scheme 6: Plausible pathway for the dimerization of pyrazolopyrimidine 8 into macrocycle 5.
Figure 1: Gibbs free energy diagram (B3LYP/6-311++G(d,p)) for the N2H4-promoted transformation of pyrazolopyr...
Scheme 7: Transformation of macrocycle 5 into pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine 13 and pyrazolo...
One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation
- Ji Ma,
- Yubin Fu,
- Junzhi Liu and
- Xinliang Feng
Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72
- nucleus-independent chemical shift (NICS) calculation was conducted. As shown in Figure 2d, the positive NICS(1) values of the five-membered rings A and C reveal the slightly anti-aromatic feature. The rings B, F and I appear to have more aromatic character, while the rings D, E, G and H become less
- . Hydrogen atoms and solvent molecules are omitted for clarity. (d) Selected bond lengths (from the crystal structure) and calculated NICS(1) values of rings A–I in 1. (e) Clar valence structure representation of 1 with three benzeneoid rings. (a) UV–vis absorption spectra of precursor 5 and 1 in CH2Cl2
Graphical Abstract
Scheme 1: Chemical structures of dicyclopenta-fused pyrene derivatives i–iii, peropyrene and the dicyclopenta...
Scheme 2: Synthetic route towards compound 1. a) B2pin2, dtbpy, [Ir(OMe)cod]2, cyclohexane, 70 °C, 20 h, 67%;...
Figure 1: High-resolution MALDI-TOF mass spectrum of 1. Inset: isotopic distribution compared to mass spectru...
Figure 2: Single-crystal X-ray structure of 1. (a) Top view and (b) side view of the (P,P) isomer. c) Crystal...
Figure 3: (a) UV–vis absorption spectra of precursor 5 and 1 in CH2Cl2 solution (10−5 M). Inset: photograph o...
Figure 4: Molecular orbitals of peropyrene derivative 6 and the dicyclopenta-fused peropyrene 1.
The activity of indenylidene derivatives in olefin metathesis catalysts
- Maria Voccia,
- Steven P. Nolan,
- Luigi Cavallo and
- Albert Poater
Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275
- the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a
- ]. In order to evaluate the change of the aromaticity of the phenyl ring of the indenylidene derivatives 3–6, we evaluated the aromaticity of the six-membered aryl rings, as well as the ring current on the five-membered ring by means of magnetic-based aromaticity criterion NICS (GIAO, see all NICS
- scaled by 1.17, and a mesh of 0.1 Å was used to scan the sphere for buried voxels. The steric maps were generated also with the SambVca package [69]. Aromaticity was evaluated by means of the nucleus independent chemical shift (NICS) [70][71], proposed by Schleyer et al., as a magnetic descriptor of
Graphical Abstract
Scheme 1: Catalysts studied by DFT calculations.
Scheme 2: Precatalyst initiation in olefin metathesis (L = NHC ligand).
Figure 1: Topographic steric maps (plane xy) of the NHC ligands of species I for the studied SIMes–Ru complex...
Figure 2: Intermediate II for catalysts a) 1 and b) 5 (important bond lengths are given in Å).
Synthesis and characterization of π–extended “earring” subporphyrins
- Haiyan Guan,
- Mingbo Zhou,
- Bangshao Yin,
- Ling Xu and
- Jianxin Song
Beilstein J. Org. Chem. 2018, 14, 1956–1960, doi:10.3762/bjoc.14.170
- antiaromatic character of the ear-containing macrocycle, which is quite similar to the analogous “earring” porphyrin [38]. Furthermore, the antiaromaticity of the ear-containing macrocycle is proved by the large positive NICS value in the hole as well as the anticlockwise ring currency (see Supporting
Graphical Abstract
Scheme 1: Synthesis of “earring” subporphyrin and its Pd complex. Synthetic procedure: (i) Diboryltripyrrane ...
Figure 1: Partial 1H NMR spectrum of 3.
Figure 2: X-ray crystal structures of 3: a) top view; b) side view. Thermal ellipsoids are drawn at the 50% p...
Figure 3: Partial 1H NMR spectrum of 3Pd.
Figure 4: X-ray crystal structures of 3Pd: a) top view; b) side view. Thermal ellipsoids are at the 30% proba...
Figure 5: UV–vis/NIR spectra of 3 and 3Pd.
One hundred years of benzotropone chemistry
- Arif Dastan,
- Haydar Kilic and
- Nurullah Saracoglu
Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98
Graphical Abstract
Scheme 1: Tropone (1), tropolone (2) and their resonance structures.
Figure 1: Natural products containing a tropone nucleus.
Figure 2: Possible isomers 11–13 of benzotropone.
Scheme 2: Synthesis of benzotropones 11 and 12.
Scheme 3: Oxidation products of benzotropylium fluoroborate (16).
Scheme 4: Oxidation of 7-bromo-5H-benzo[7]annulene (22).
Scheme 5: Synthesis of 4,5-benzotropone (11) using o-phthalaldehyde (27).
Scheme 6: Synthesis of 4,5-benzotropone (11) starting from oxobenzonorbornadiene 31.
Scheme 7: Acid-catalyzed cleavage of oxo-bridge of 34.
Scheme 8: Synthesis of 4,5-benzotropone (11) from o-xylylene dibromide (38).
Scheme 9: Synthesis of 4,5-benzotropone (11) via the carbene adduct 41.
Scheme 10: Heck coupling strategy for the synthesis of 11.
Scheme 11: Synthesis of benzofulvalenes via carbonyl group of 4,5-benzotropone (11).
Figure 3: Some cycloheptatrienylium cations.
Scheme 12: Synthesis of condensation product 63 and its subsequent oxidative cyclization products.
Figure 4: A novel series of benzo[7]annulenes prepared from 4,5-benzotropone (11).
Scheme 13: Preparation of substituted benzo[7]annulene 72 using the Mukaiyama-Michael reaction.
Figure 5: Possible benzo[7]annulenylidenes 73–75.
Scheme 14: Thermal and photochemical decomposition of 7-diazo-7H-benzo[7]annulene (76) and the trapping of int...
Scheme 15: Synthesis of benzoheptafulvalene 86.
Scheme 16: Synthesis of 7-(diphenylmethylene)-7H-benzo[7]annulene (89).
Scheme 17: Reaction of 4,5-benzotropone (11) with dimethyl diazomethane.
Scheme 18: Synthesis of dihydrobenzomethoxyazocine 103.
Scheme 19: Synthesis and reducibility of benzo-homo-2-methoxyazocines.
Scheme 20: Synthesis of 4,5-benzohomotropones 104 and 115 from 4,5-benzotropones 11 and 113.
Scheme 21: A catalytic deuterogenation of 4,5-benzotropone (11) and synthesis of 5-monosubstituted benzo[7]ann...
Scheme 22: Synthesis of methyl benzo[7]annulenes 131 and 132.
Scheme 23: Ambident reactivity of halobenzo[7]annulenylium cations 133a/b.
Scheme 24: Preparation of benzo[7]annulenylidene–iron complexes 147.
Scheme 25: Synthesis of 1-ethynylbenzotropone (150) and the etheric compound 152 from 4,5-benzotropone (11) wi...
Scheme 26: Thermal decomposition of 4,5-benzotropone (11).
Scheme 27: Reaction of 4,5-benzotropone (11) with 1,2-ethanediol and 1,2-ethanedithiol.
Scheme 28: Conversions of 1-benzosuberone (162) to 2,3-benzotropone (12).
Scheme 29: Synthesis strategies for 2,3-bezotropone (12) using 1-benzosuberones.
Scheme 30: Oxidation-based synthesis of 2,3-benzotropone (12) via 1-benzosuberone (162).
Scheme 31: Synthesis of 2,3-benzotropone (12) from α-tetralone (171) via ring-expansion.
Scheme 32: Preparation of 2,3-benzotropone (12) by using of benzotropolone 174.
Figure 6: Benzoheptafulvenes as condensation products of 2,3-benzotropone (12).
Scheme 33: Conversion of 2,3-benzotropone (12) to tosylhydrazone salt 182 and gem-dichloride 187.
Figure 7: Benzohomoazocines 191–193 and benzoazocines 194–197.
Scheme 34: From 2,3-benzotropone (12) to carbonium ions 198–201.
Scheme 35: Cycloaddition reactions of 2,3-benzotropone (12).
Scheme 36: Reaction of 2,3-benzotropone (12) with various reagents and compounds.
Figure 8: 3,4-Benzotropone (13) and its resonance structure.
Scheme 37: Synthesis of 6,7-benzobicyclo[3.2.0]hepta-3,6-dien-2-one (230).
Figure 9: Photolysis and thermolysis products of 230.
Figure 10: Benzotropolones and their tautomeric structures.
Scheme 38: Synthesis strategies of 4,5-benzotropolone (238).
Scheme 39: Synthesis protocol for 2-hydroxy-4,5-benzotropone (238) using oxazole-benzo[7]annulene 247.
Figure 11: Some quinoxaline and pyrazine derivatives 254–256 prepared from 4,5-benzotropolone (238).
Scheme 40: Nitration product of 4,5-benzotropolone (238) and its isomerization to 1-nitro-naphthoic acid (259)....
Scheme 41: Synthesis protocol for 6-hydroxy-2,3-benzotropone (239) from benzosuberone (162).
Scheme 42: Various reactions via 6-hydroxy-2,3-benzotropone (239).
Scheme 43: Photoreaction of 6-hydroxy-2,3-benzotropone (239).
Scheme 44: Synthesis of 7-hydroxy-2,3-benzotropone (241) from benzosuberone (162).
Scheme 45: Synthesis strategy for 7-hydroxy-2,3-benzotropone (241) from ketone 276.
Scheme 46: Synthesis of 7-hydroxy-2,3-benzotropone (241) from β-naphthoquinone (280).
Scheme 47: Synthesis of 7-hydroxy-2,3-benzotropone (241) from bicyclic endoperoxide 213.
Scheme 48: Synthesis of 7-hydroxy-2,3-benzotropone (241) by ring-closing metathesis.
Figure 12: Various monosubstitution products 289–291 of 7-hydroxy-2,3-benzotropone (241).
Scheme 49: Reaction of 7-hydroxy-2,3-benzotropone (241) with various reagents.
Scheme 50: Synthesis of 4-hydroxy-2,3-benzotropones 174 and 304 from diketones 300/301.
Scheme 51: Catalytic hydrogenation of diketones 300 and 174.
Scheme 52: Synthesis of halo-benzotropones from alkoxy-naphthalenes 306, 307 and 310.
Figure 13: Unexpected byproducts 313–315 during synthesis of chlorobenzotropone 309.
Figure 14: Some halobenzotropones and their cycloadducts.
Scheme 53: Multisep synthesis of 2-chlorobenzotropone 309.
Scheme 54: A multistep synthesis of 2-bromo-benzotropone 26.
Scheme 55: A multistep synthesis of bromo-2,3-benzotropones 311 and 316.
Scheme 56: Oxidation reactions of 8-bromo-5H-benzo[7]annulene (329) with some oxidants.
Scheme 57: Synthesis of 2-bromo-4,5-benzotropone (26).
Scheme 58: Synthesis of 6-chloro-2,3-benzotropone (335) using LiCl and proposed intermediate 336.
Scheme 59: Reaction of 7-bromo-2,3-benzotropone (316) with methylamine.
Scheme 60: Reactions of bromo-2,3-benzotropones 26 and 311 with dimethylamine.
Scheme 61: Reactions of bromobenzotropones 311 and 26 with NaOMe.
Scheme 62: Reactions of bromobenzotropones 26 and 312 with t-BuOK in the presence of DPIBF.
Scheme 63: Cobalt-catalyzed reductive cross-couplings of 7-bromo-2,3-benzotropone (316) with cyclic α-bromo en...
Figure 15: Cycloadduct 357 and its di-π-methane rearrangement product 358.
Scheme 64: Catalytic hydrogenation of 2-chloro-4,5-benzotropone (311).
Scheme 65: Synthesis of dibromo-benzotropones from benzotropones.
Scheme 66: Bromination/dehydrobromination of benzosuberone (162).
Scheme 67: Some transformations of isomeric dibromo-benzotropones 261A/B.
Scheme 68: Transformations of benzotropolone 239B to halobenzotropolones 369–371.
Figure 16: Bromobenzotropolones 372–376 and 290 prepared via bromination/dehydrobromination strategy.
Scheme 69: Synthesis of some halobenzotropolones 289, 377 and 378.
Figure 17: Bromo-chloro-derivatives 379–381 prepared via chlorination.
Scheme 70: Synthesis of 7-iodo-3,4-benzotropolone (382).
Scheme 71: Hydrogenation of bromobenzotropolones 369 and 370.
Scheme 72: Debromination reactions of mono- and dibromides 290 and 375.
Figure 18: Nitratation and oxidation products of some halobenzotropolenes.
Scheme 73: Azo-coupling reactions of some halobenzotropolones 294, 375 and 378.
Figure 19: Four possible isomers of dibenzotropones 396–399.
Figure 20: Resonance structures of tribenzotropone (400).
Scheme 74: Two synthetic pathways for tribenzotropone (400).
Scheme 75: Synthesis of tribenzotropone (400) from dibenzotropone 399.
Scheme 76: Synthesis of tribenzotropone (400) from 9,10-phenanthraquinone (406).
Scheme 77: Synthesis of tribenzotropone (400) from trifluoromethyl-substituted arene 411.
Figure 21: Dibenzosuberone (414).
Figure 22: Reduction products 415 and 416 of tribenzotropone (400).
Figure 23: Structures of tribenzotropone dimethyl ketal 417 and 4-phenylfluorenone (412) and proposed intermed...
Figure 24: Structures of benzylidene- and methylene-9H-tribenzo[a,c,e][7]annulenes 419 and 420 and chiral phos...
Figure 25: Structures of tetracyclic alcohol 422, p-quinone methide 423 and cation 424.
Figure 26: Structures of host molecules 425–427.
Scheme 78: Synthesis of non-helical overcrowded derivatives syn/anti-431.
Figure 27: Hexabenzooctalene 432.
Figure 28: Structures of possible eight isomers 433–440 of naphthotropone.
Scheme 79: Synthesis of naphthotropone 437 starting from 1-phenylcycloheptene (441).
Scheme 80: Synthesis of 10-hydroxy-11H-cyclohepta[a]naphthalen-11-one (448) from diester 445.
Scheme 81: Synthesis of naphthotropone 433.
Scheme 82: Synthesis of naphthotropones 433 and 434 via cycloaddition reaction.
Scheme 83: Synthesis of naphthotropone 434 starting from 452.
Figure 29: Structures of tricarbonyl(tropone)irons 458, and possible cycloadducts 459.
Scheme 84: Synthesis of naphthotropone 436.
Scheme 85: Synthesis of precursor 465 for naphthotropone 435.
Scheme 86: Generation of naphthotropone 435 from 465.
Figure 30: Structures of tropylium cations 469 and 470.
Figure 31: Structures of tropylium ions 471+.BF4−, 472+.BF4−, and 473+.BF4−.
Scheme 87: Synthesis of tropylium ions 471+.BF4− and 479+.ClO4−.
Scheme 88: Synthesis of 1- and 2-methylanthracene (481 and 482) via carbene–carbene rearrangement.
Figure 32: Trapping products 488–490.
Scheme 89: Generation and chemistry of a naphthoannelated cycloheptatrienylidene-cycloheptatetraene intermedia...
Scheme 90: Proposed intermediates and reaction pathways for adduct 498.
Scheme 91: Exited-state intramolecular proton transfer of 505.
Figure 33: Benzoditropones 506 and 507.
Scheme 92: Synthesis of benzoditropone 506e.
Scheme 93: Synthetic approaches for dibenzotropone 507 via tropone (1).
Scheme 94: Formation mechanisms of benzoditropone 507 and 516 via 515.
Scheme 95: Synthesis of benzoditropones 525 and 526 from pyromellitic dianhydride (527).
Figure 34: Possible three benzocyclobutatropones 534–536.
Scheme 96: Synthesis of benzocyclobutatropones 534 and 539.
Scheme 97: Synthesis attempts for benzocyclobutatropone 545.
Scheme 98: Generation and trapping of symmetric benzocyclobutatropone 536.
Scheme 99: Synthesis of chloro-benzocyclobutatropone 552 and proposed mechanism of fluorenone derivatives.
Scheme 100: Synthesis of tropolone analogue 559.
Scheme 101: Synthesis of tropolones 561 and 562.
Figure 35: o/p-Tropoquinone rings (563 and 564) and benzotropoquinones (565–567).
Scheme 102: Synthesis of benzotropoquinone 566.
Scheme 103: Synthesis of benzotropoquinone 567 via a Diels–Alder reaction.
Figure 36: Products 575–577 through 1,2,3-benzotropoquinone hydrate 569.
Scheme 104: Structures 578–582 prepared from tropoquinone 567.
Figure 37: Two possible structures 583 and 584 for dibenzotropoquinone, and precursor compound 585 for 583.
Scheme 105: Synthesis of saddle-shaped ketone 592 using dibenzotropoquinone 584.
Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores
- Huixin Jiang,
- Virginia Mazzanti,
- Christian R. Parker,
- Søren Lindbæk Broman,
- Jens Heide Wallberg,
- Karol Lušpai,
- Adam Brincko,
- Henrik G. Kjaergaard,
- Anders Kadziola,
- Peter Rapta,
- Ole Hammerich and
- Mogens Brøndsted Nielsen
Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104
- that required to reduce the acyclic TEE compound 1a (−1.70 V vs Fc/Fc+) [10]. We explained this readiness of 2a to accommodate electrons by a gain of aromaticity; a resonance form with a 14 πz core can be drawn for the dianion and a diatropic ring-current was supported by NICS calculations. The new
Graphical Abstract
Figure 1: TTF dimers with linearly or cross-conjugated bridging units, acyclic or cyclic bridging units.
Scheme 1: Synthesis of TTF dimers with alkyne bridges. TMEDA = N,N,N’,N’-tetramethylethylenediamine. MS = mol...
Scheme 2: Synthesis of TTF dimers with TEE and diethynylpyridine bridges.
Scheme 3: Synthesis of TTF dimer with radiaannulene core.
Figure 2: Molecular structure of 8 (top) and packing diagram (bottom). Crystals were grown from CH2Cl2/MeOH. ...
Figure 3: Bond angles for the cyclic core of 8 (X-ray crystal structure data).
Figure 4: Cyclic voltammograms obtained for the oxidation of compounds 1a ([10]), 2a ([10]), and 3b–8 (this work, ca....
Figure 5: Selected bis-TTFs from literature [20-23].
Figure 6: Cyclic voltammograms obtained for the reduction of compounds 1a, 2a, 6, and 8 in CH2Cl2 (0.1 M Bu4N...
Figure 7: One possible resonance form of the radical anion of 8 with a 14 πz aromatic core.
Scheme 4: Spin–spin interactions resulting from oxidation of TTFdimers.
Figure 8: In situ EPR−UV–vis–NIR cyclic voltammetry of 2b (1 mM) (a) potential dependence of difference vis–N...
Figure 9: In situ EPR−UV–vis–NIR cyclic voltammetry of 4 (0.4 mM): (a) potential dependence of difference vis...
Figure 10: Vis–NIR spectral changes observed during anodic oxidation of each TTF unit to cation radical within...
Figure 11: UV–vis–NIR absorptions of 1b (2.4 mM), 4 (3.5 mM), 5 (2.9 mM), and 8 (1.9 mM) in CH2Cl2 + 0.1 M Bu4...
Figure 12: In situ EPR−UV–vis–NIR cyclic voltammetry of 2b (1 mM) in the cathodic region: (a) potential depend...
Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes
- María Martín-Rodríguez,
- Luis M. Castelló,
- Carmen Nájera,
- José M. Sansano,
- Olatz Larrañaga,
- Abel de Cózar and
- Fernando P. Cossío
Beilstein J. Org. Chem. 2013, 9, 2422–2433, doi:10.3762/bjoc.9.280
- : asymmetric catalysis; DFT; 1,3-dipolar cycloaddition; gold catalysis; NICS; NTR; oxazolones; prolines; Introduction The synthesis of α-amino acids employing an α-amino carbonyl template constitutes the most straightforward route to introduce the α-side chain [1]. As a valid example, oxazol-5-(4H)-ones
- described in a preliminary communication [28] concerning the catalytic activity of complexes 3 and 4 in the 1,3-DC of oxazolones with electrophilic alkenes. Here, a deep DFT analysis and the application of other computational experiments (NRT, NICS) were compared to the experimentally observed results in
- negative charge in the Lewis structure of Ylide I is mainly placed on C5. In the case of Ylide II, this negative charge is placed on the oxygen of the carboxy group instead. The importance of these electronic distributions was verified by Nucleus Independent Chemical Shifts (NICS) calculations in the ring
Graphical Abstract
Figure 1: Chiral gold(I) complexes employed in 1,3-DC involving azomethine ylides.
Scheme 1: 1,3-DC of azlactone 5a and NPM.
Scheme 2: General 1,3-DC between azlactones 5 with maleimides.
Scheme 3: Formation of the amide 8aa.
Figure 2: Positive non-linear effects (NLE) observed in 1,3-DC of azlactone 7aa and NPM.
Figure 3: Main geometrical features and relative Gibbs free energies (in kcal mol−1 at 298 K) of complexes [(S...
Figure 4: Main geometrical features and relative Gibbs free energies (in kcal mol−1) of the less energetic tr...
Scheme 4: Reaction Gibbs free energy associated with the 1,3-DC of 5aa and NPM catalyzed by (Sa)-Binap gold d...
Scheme 5: ΔG calculation for the recovery of the catalytic active species.
Scheme 6: 1,3-DC of azlactone 10 and tert-butyl acrylate.
Figure 5: (A) Schematic representation of the model gold(I) ylides. (B) HOMO of the ylides and expansion orbi...
Figure 6: Main geometrical features and relative Gibbs free energies (in kcal mol−1 at 298 K) of complexes [{(...
Figure 7: Main geometrical features and relative Gibbs free energies (in kcal mol−1) of the less energetic tr...
Scheme 7: Reduction of heterocycle 7aa under different conditions.
Scheme 8: Double 1,3-DC to give polycycle 15.
Scheme 9: Reaction between 7aa and nitrostyrene.
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
- chemical shifts (NICS) [109][110][111], which are considered to be a measure of aromaticity. In agreement with the almost equal lengths of the exocyclic C–C bonds in 45a (136.1 pm) and 45c (135.4 pm), as determined by X-ray crystallography, none of the two heterocyclic rings in 47a and 47c shows aromatic
- character (NICS(1)). However, while the electrophilic addition to the exocyclic double bond of 47a yields the cyclic conjugated 6π system in 48a, the analogous electrophilic addition to 47c yields the nonaromatic amidinium ion 48c. The high nucleophilicity of 45a, which is mirrored by the high proton
- ]) of the corresponding carbenes 49a–c (in kJ mol–1, MP2/6-31+G(2d,p)//B98/6-31G(d)), and the NICS(1) values of 47–49 (B3LYP/6-311+G(d)) (from [107]). Berkessel’s synthesis of a Breslow intermediate (51, keto tautomer) from carbene 43 [112]. Synthesis of O-methylated Breslow intermediates [114
Graphical Abstract
Figure 1: Second-order rate constants for reactions of electrophiles with nucleophiles.
Figure 2: Mechanism of amine-catalyzed conjugate additions of nucleophiles [23-28].
Figure 3: Kinetics of the reactions of the iminium ion 3a with the silylated ketene acetal 7a [35].
Figure 4: Laser flash photolytic generation of iminium ions 3a.
Figure 5: Correlations of the reactivities of the iminium ions 3a and 3b toward nucleophiles with the corresp...
Figure 6: Comparison of the electrophilicities of cinnamaldehyde-derived iminium ions 3a–3i.
Figure 7: Nucleophiles used in iminium activated reactions [35,42,44-52].
Figure 8: Counterion effects in electrophilic reactions of iminium ions 3a-X (at 20 °C, silyl ketene acetal 7b...
Figure 9: Comparison of calculated and experimental rate constants of electrophilic aromatic substitutions wi...
Figure 10: Aza-Michael additions of the imidazoles 15 with the iminium ion 3a [58].
Figure 11: Plots of log k2 for the reactions of enamides 17a–17e with the benzhydrylium ions 18a–d in CH3CN at...
Figure 12: Comparison of the nucleophilicities of enamides 17 with those of several other C nucleophiles (solv...
Figure 13: Experimental and calculated rate constants k2 for the reactions of 17b and 17g with 3a and 3b in th...
Figure 14: Comparison between experimental and calculated (Equation 1) cyclopropanation rate constants [64].
Figure 15: Electrostatic activation of iminium activated cyclopropanations with sulfur ylides.
Figure 16: Sulfur ylides inhibit the formation of iminium ions.
Figure 17: Enamine activation [65].
Figure 18: Electrophilicity parameters E for classes of compounds that have been used as electrophilic substra...
Figure 19: Quantification of the nucleophilic reactivities of the enamines 32a–e in acetonitrile (20 °C) [83]; a d...
Figure 20: Proposed transition states for the stereogenic step in proline-catalyzed reactions.
Figure 21: Kinetic evidence for the anchimeric assistance of the electrophilic attack by the carboxylate group....
Figure 22: Differentiation of nucleophilicity and Lewis basicity (in acetonitrile at 20 °C): Rate (left) and e...
Figure 23: NHCs 41, 42, and 43 are moderately active nucleophiles and exceptionally strong Lewis bases (methyl...
Figure 24: Nucleophilic reactivities of the deoxy Breslow intermediates 45 in THF at 20 °C [107].
Figure 25: Comparison of the proton affinities (PA, from [107]) of the diaminoethylenes 47a–c with the methyl catio...
Figure 26: Berkessel’s synthesis of a Breslow intermediate (51, keto tautomer) from carbene 43 [112].
Figure 27: Synthesis of O-methylated Breslow intermediates [114].
Figure 28: Relative reactivities of deoxy- and O-methylated Breslow intermediates [114].
Figure 29: Reactivity scales for electrophiles and nucleophiles relevant for organocatalytic reactions (refere...
Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues
- Helen Jansen,
- J. Chris Slootweg and
- Koop Lammertsma
Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201
- -orbitals [41], as is the case for cyclohepta-1,3,5-triene (1) [19][20]. Through the use of nucleus-independent chemical shifts (NICS(1)) [48], it was shown that thiepine (−2.3 ppm) [49] and phenyl phosphepine (−4.8 ppm) [7] display aromatic character when compared to the well-known 6π-electron Hückel
- -aromatic tropylium cation [46], which has a NICS(1) value of −8.2 ppm. Adding electronegative substituents enhances the effect, and fully aromatic systems are obtained after complete fluorination of the heteropines (Figure 1) [50]. In contrast, the flattened transition structures for ring inversion of
- thiepine and phosphepine are indeed highly antiaromatic planar 8π-electron systems, with positive NICS(1) values of 19.3 [47] and 6.4 ppm [7], respectively. The inherent instability of thiepine (5) has been attributed to this effect [51][52]. Oxepine – benzene oxide Oxepine (3) was isolated first by Vogel
Graphical Abstract
Scheme 1: Valence isomerization of cyclohepta-1,3,5-triene (1) and its heteroelement analogues.
Scheme 2: Conformational ring inversions.
Scheme 3: Rearrangements of the parent cycloheptatriene 1 and norcaradiene 2.
Figure 1: NICS(0) values of fluorinated heteropines.
Scheme 4: Reactivity of oxepine (3) and benzene oxide (4).
Figure 2: Stabilized thiepines 15–18.
Scheme 5: Valence isomerization of 1H-azepines.
Scheme 6: Reactivity of 1H-azepine.
Figure 3: Benzannulated azepines 27 and 28.
Figure 4: Reported phosphepines 29–32.
Scheme 7: Phosphinidene generation from metal-complexed benzophosphepine 33.
