Anisotropieeffekte konjugierter cyclischer Systeme, V. ¹ H‐NMR‐Spektren mesitylsubstituierter aromatischer 6π‐Systeme

Abstract

1,3-Dimethy1-2-mesitylcyclopentadien (5) wird auf zwei Wegen hergestellt. Das 'H-NMR-Spektrum des Cyclopentadienyl-Anions 3 zeigt eine Differenz der chemischen Verschiebungen zwischen den p -und o-Methylgruppensignalen A 6 = 0.25 ppm. Dieser im Vergleich zu Bimesityl (2b) ( A 6 = 0.47 ppm) und zum Tropylium-Ion 1 ( A 6 = 0.56 pprn) niedrige Wert wird mit dem EinfluB der hohen x-Elektronendichte im Anionfunfring auf die Methylgruppen durch den Raum erklart. Dafur wird im Bereich 1 bis 3 eine lineare Beziehung gefunden. Die Rdntgenstrukturanalyse des aus 3 erhaltenen Ferrocens 18 zeigt, daR die Mesityl-und Cyclopentadienyl-Ringe senkrecht aufeinander stehen. Anisotropy Effects of Conjugated Cyclic Systems, V1)'H NMR Spectra of Mesityl Substituted Aromatic 6n Systems 1,3-Dimethyl-2-mesitylcyclopentadiene (5) has been synthesized in two routes. The 'H NMR spectrum of the cyclopentadienyl anion 3 shows a difference of chemical shift values of the p -and o-rnethyl groups of A 6 = 0.25 ppm. Compared with bimesityl (2b) (A6 = 0.47 ppm) and the tropylium ion 1 ( A 6 = 0.56 ppm) this is a small A 6 value. This is interpreted by the influence of the x electron density from the five-membered anion ring on the methyl groups through space. In the range 1 to 3 there is found a linear relationship for this influence. X-ray analysis of the ferrocene derivative 18 prepared from 3 confirms the perpendicular orientation of the mesityl and cyclopentadienyl rings.In einer fruheren Mitteilung ') konnte gezeigt werden, dal3 die Differenzen der chemischen Verschiebungen zwischen den 'H-NMR-Signalen der p -und o-Methylgruppen AS in mesitylsubstituierten 2,6-Dimethylbenzol-Derivaten 2 nur sehr wenig um den Wert des als Standard gewahlten Bimesityls (2b) (AS = 0.47 ppm) schwanken, wobei elektronenziehende Substituenten wie R = CN in 2a (AS = 0.52 ppm) zu hdheren und elektronenspendende Substituenten, z. B. R = OCH, in 2c (AS = 0.44 ppm), zu niedrigeren Werten fuhren.Da Substituenteneffekte auf den A6-Wert klein sind, ist es gestattet, diese AS-Werte als Kriterium fur den aromatischen Charakter mesitylsubstituierter cyclischer Systeme anzusehen. In diesem Zusammenhang war es von Interesse, den EinfluB von ganzen

Crystal structures of o-, m,- and p-nitrophenylferrocenes and their relevance to other sterically crowded phenylferrocenes

“…Crystal Dutu .for (1).-C,,H,,FeNO2, M = 307.1, monoclinic, space group P2,/a, a = 14.112(8), b = 10.660 (7), c = 8.905(8) A, p = 101.5(1)", U = 1312.7 A3, D, = 1.55, D, = 1.55 g cm-,, h(Mo-K,) = 0.7107 A, p = 11.78 cm-', Angles between least-squares planes * respectively and molecular dimensions are compared in Table 4.…”

“…(3)] have been determined. All three structures consist of discrete molecules with the iron atom q5-bonded t o both cyclopentadienyl rings with bond lengths in the range 1.997(9)-2.120 (10) A. The steric constraints of the nitro group lead t o different conformations in the three structures.…”

Pd(0)-Catalyzed Conjugate Addition of Benzylzinc Chlorides to α,β-Enones in an Atmosphere of Carbon Monoxide: Preparation of 1,4-Diketones

“…1-(2,4,6-Trimethylphenyl)hexane-2,5-dione (3m): 3:1 hexane/EtOAc; a colorless oil (60%); bp 129 °C/0.2 mmHg, mp 29−31 °C (Et 2 O−hexane) [lit . mp 32 °C]; IR (neat) 1711, 1614, 1486 cm -1 ; 1 H NMR (270 MHz) δ 2.16 (s, 3H), 2.21 (s, 6H), 2.25 (s, 3H), 2.66 (m, 4H), 3.77 (s, 2H), 6.86 (s, 2H); 13 C NMR (68 MHz) δ 20.2 (t), 20.8 (t), 29.8 (t), 35.3 (t), 36.9 (t), 43.9 (t), 128.8 (d), 136.3(s), 136.7 (s), 207.06 (s), 207.09 (s); EI-MS m / z (rel intensity) 232 (M + , 14), 133 (88), 99 (100), 71 (7).…”

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…In the study on the synthesis of ferrocenes, a pinacol rearrangement of (hydroxymesityl)cyclobutanone 623 was executed via treatment with 1.2 equiv of trifluoroacetic acid at room temperature for one hour, affording the corresponding ring expanded product 624 in 42% yield (Scheme 170). 239 The latter compounds served as substrates for the preparation of iron complex 625. In analogy with sesquiterpene syntheses described in the previous section, a synthesis toward filiformin 152 by means of a semipinacol rearrangement has been reported.…”

“…In the study on the synthesis of ferrocenes, a pinacol rearrangement of (hydroxymesityl)cyclobutanone 623 was executed via treatment with 1.2 equiv of trifluoroacetic acid at room temperature for 1 h, affording the corresponding ring-expanded product 624 in 42% yield (Scheme ) . The latter compounds served as substrates for the preparation of iron complex 625 .…”