Stereodynamics and Conformational Chirality of the Atropisomers of Ditolyl Anthrones and Anthraquinone

Abstract

Syn and anti conformers in similar proportions were observed at ambient temperature for the title compounds. The conformational assignment of the two anthrones was obtained by the observation of different multiplicity of the methylene NMR signals, whereas that of the anthraquinone derivative was determined by NOE experiments. The anti-to-syn interconversion barriers were obtained by line-shape simulation of the temperature-dependent NMR spectra, and by saturation transfer experiments. In one case the X-ray diffraction indicated that the syn is the only structure observed in the crystals.

Tautomerism and Atropisomerism in Free‐Base (meso)‐Strapped Porphyrins: Static and Dynamic Aspects

“…Although some significant variations in the entropy of atropisomerisation processes have been reported for some cases, for example, in push-pull-type biphenyl atropisomers (DS°up to À120 J mol À1 ), [85,86] the DS°values of pure dynamic conformational processes are most often negligible and usually do not exceed a few J mol À1 , which lies within experimental error. [84][85][86][87][88][89] Moreover, considering the same symmetry number [90] (s = 2) for S2 (average C 2v ) and S3 (average C 2h ), and assuming the distortion modes and planarity to be similar for both porphyrin macrocycles, there is no obvious reason to expect any significant difference between the entropy energies of S2 and S3 (although the significant difference in their dipole moments may influence their entropy and/or enthalpy through solvation effects). [76,91] It is therefore reasonable to assume that, in our case, the variation in entropy for the interconversion of the S2 and S3 atropisomers must be at least negligible with respect to the highly enthalpic-dependent energy barriers to rotation.…”

Recent Advances in Stereodynamics and Conformational Analysis by Dynamic NMR and Theoretical Calculations

“…When the 1-and 8-substituents are ortho-toluenes (11b) they are stereolabile conformers, [82] whereas when the substituents are the more hindered 2-methyl-1-naphthyl groups (11a) the syn and anti isomers (red-and yellow-coloured, respectively, as in Figure S-5 in the Supporting Information) are sufficiently stable to be separated. [83] Their interconversion barrier has been determined as 35.4 kcal mol -1 , with the anti form more stable under equilibrium conditions (59:41 at +140°C).…”

Synthesis of Novel Symmetrical and Unsymmetrical o-Phthalic Acid Diamides

“…Alternatively, this compound was prepared by treating 2-(piperazine-1-carbonyl)benzoic acid 3b withdiethylamine 2a by HATU and Et 3 N at 0-5 ∘ C for 40-45 min in DMF to form N,Ndiethyl-2-(piperazine-1-carbonyl)benzamide 5a. This reaction was examined by carrying out the condensation of 2-(diethylcarbonyl)benzoic acid 3a (1 mmol) with piperazine 2b (1 mmol) in the presence different coupling reagents (HATU, EDC.HCl/HOBt (1-hydroxybenzotriazole), DCC (N,N -dicyclohexylcarbodiimide), HBTU and PTSA (4-methylbenzenesulfonic acid)) and tertiary bases (Et 3 N and DBU (2,3,4,6,7,8,9, 10-octahydropyrimido [1, 2-a] azepine) at different temperatures in DMF as a solvent (Table 1) with a view to study the generalisation of condensation between 3 and 2. However, coupling of 3a with 2b in the presence of HATU and Et 3 N at 0-5 ∘ C for 40-45 min in DMF was found to be the best method giving 5a in quality and yield (≥80%) ( Table 1, entry 1).…”

“…It is used in the manufacture of phenolphthalein indicator [3,4], anthraquinone [5] (a versatile, raw materials in the dye industry [6]), and metal phthalocyanines [7]. Phthalocyanine compounds are used in a variety of applications [7] in addition to their use as pigments, in paints [8] and in many types of dyestuffs [7].…”