Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Wiadomości Chemiczne

2 2017

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: axially chiral biaryls

Sortuj według:

Ogranicz wyniki do:

Atroposelektywna synteza naturalnych chiralnych osiowo związków biarylowych. Część 2

Kołodziejska R., Tafelska-Kaczmarek A., Studzińska R.

Wiadomości Chemiczne

2017

[Z] 71, 3-4

199--217

A direct aryl-aryl coupling reaction is the most common method for the synthesis of axially chiral biaryls. Atroposelective coupling can be accomplished by three main strategies (Scheme 1) [1, 11]: a) intramolecular coupling reaction between two aryl substrates by the use of the chiral tether as a source of asymmetric information (Scheme 2), b) intermolecular reaction of the modified aryl compounds containing a chiral auxiliary. A source of chiral information can be a planar-chiral element, the chiral leaving group, and the chiral ortho substituent (Scheme 12, 16, 17), c) intermolecular coupling in the presence of chiral additives, for example, stoichiometric or catalytic oxidation in the presence of the transition metal complexes containing chiral ligands, and the redox-neutral coupling reactions catalyzed by transition metal complexes with chiral bidentate N/P- -ligands (Scheme 18, 20–22). These methods have been applied in the synthesis of various biologically active compounds. For example, Lipshutzet et al. obtained a fragment of the antibiotic vancomycin [15], and O-permethyltellimagrandin II [16]. Lin and coworkers synthesized (P)-kotanin [17], the natural metabolite from Aspergillus glaucus (Scheme 3). Waldvogel and coworkers [19] received steganacin derivative, a cytostatic drug (Scheme 5). Coleman et al. in the oxidative dimerization reaction of aryls with a chiral ortho substituents obtained a precursor in the synthesis of calphostin A (Scheme 8) [26]. Meyers and coworkers [27, 28] applied the Ullmann homocoupling for the synthesis of gossypol (Scheme 9). The oxidative coupling of phenols allows to obtain the natural precursor of nigerone (Scheme 13) [42]. Whereas the calphostin [18] derivative, an inhibitor of protein kinase C, was obtained by the oxidative coupling reaction (Scheme 4). The schizandrin [23] from Schisandra chinensis and isodiospyrin [24] from Diospyros morrisiana were obtained by intermolecular coupling reaction of aryl substrates with the chiral ortho substituents (Scheme 7).

Atroposelektywna synteza naturalnych chiralnych osiowo związków biarylowych. Część 1

Kołodziejska R., Tafelska-Kaczmarek A., Studzińska R.

Wiadomości Chemiczne

2017

[Z] 71, 3-4

177--197

In early twentieth century, it was already known that chemical compounds might be chiral without containing the chiral atoms. The presence of the stereogenic center is a sufficient but not necessary condition that the molecule appears in two forms which are mirror images. In certain cases, the limit of free rotation in the molecule may result in asymmetry, e.g. inhibition of rotation around single bond leads to axial isomers. This is the kind of conformational isomerism, which according to the nomenclature is called atropisomerism [1, 2]. The most often optically active molecules without stereogenic atoms, possessing an axial chirality are biaryls, which are commonly found in nature. In most cases, pharmacological activity of biaryls is associated with the presence of axial chirality (Figs 1, 2; Scheme 1) [1–14]. Generally chiral biaryls are divided into bridged biaryls (Scheme 4–6) [15–24], and biaryls, which do not contain the additional ring (Scheme 2, 3) [25–33]. The thermal stability of both enantiomeric/diastereomeric forms is an essential precondition for atropisomerism. For a given temperature, conformationally stable isomers may coexist when their a half-life is at least 1000 s, which gives the minimum energy barrier of 93 kJ mol–1 at 300 K. Chiral biaryls can be achieved by either desymmetrization of stable but achiral biaryls by modifying one of the groups on the aromatic moiety (Scheme 7–9) [1, 34, 35], or by dynamic kinetic resolution of racemic mixtures of the conformationally unstable chiral substrates. The synthesis of the chirally stable biaryls from the chiral labile substrates is most frequently the result of the extra substituent addition (Scheme 10) [36], and formation or cleavage of a bridge (Scheme 11–16) [37–54]. The axially chiral biaryls can also be obtained in the atroposelective transformation of the alkyl substituent of the arene ring into a second aromatic ring in the presence of an organometallic catalyst (Scheme 17, 18) [55, 56].