Enantioselective addition of diethylzinc to benzaldehyde in the presence of sulfur-containing pyridine ligands

Chiral Aryl Pyridyl Alcohols as Enantioselective Catalysts in the Addition of Diethylzinc to Substituted Benzaldehydes

“…[50][51][52][53] The stereochemical outcome depends mainly on the stereogenic centers in the 8-position of the pyridyl-pinane-ring (ligand 8). 45 In fact, the benzaldehyde asymmetrically alkylated using diethylzinc was affected by the aromatic groups at the 5-position of ligands (Scheme II, Table 4). The enantioselectivities obtained using the 5-(pyridin-4-yl)-substituted ligand 8 were in the range 19-86% ee.…”

“…This substitution yields ligands 6-10. 45,46 This characteristic affects the steric interactions between the ligand and the substrate, both coordinated to the metal, and, therefore, the stereoselectivity.…”

Synthesis of various camphor-based chiral pyridine derivatives

“…37,38 In contrast to the great variety of ligands based on the pyridine framework, which have proven to give very good levels of enantioselectivity in the catalyzed asymmetric C-C bond forming reactions with allylic compounds, 10 rare examples of application in this reaction of sulphur-containing pyridine ligands have been reported. [40][41][42][43] In order to define the scope and limitations of thienylpyridines as chiral controllers for asymmetric catalysis, Chelucci et al have first examined these N-S ligands in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2enylacetate with dimethyl malonate, which serve as a model substrate and reagent to compare the outcome of different ligands(Figure 7). 36 Though the protocol using the malonate anion obtained by Trost's procedure is generally the best way to carry out allylic substitution reactions, the use of preformed sodium dimethyl malonate, generated by the use of sodium hydride in THF, may in some cases offer best results.…”

Enantioselective Alkynylation of 2‐Trifluoroacetyl Imidazoles Catalyzed by Bis‐Cyclometalated Rhodium(III) Complexes Containing Pinene‐Derived Ligands

“…Reduced loadings of D-RhPP (entries 7a nd 8) and the base triethylamine (entry 9) affect the reactionr ate but not the enantioselectivity.C onveniently,t he catalytic reaction can even be performed in an open flask since it is not sensitive to air or water (entries 10 and 11). Although the iridium congeners D-a nd L-IrPP (entries 12 and 13) provide inferior results, our previously developed catalysts RhO, IrO or IrS are not able to catalyze the conversiono f3c+ 4a!5c at all (entries [14][15][16]. Thus, although the absolute configurationa tt he ligand does not effect the rate and degree of asymmetric induction, the nature of the ligand is evidently crucial for an effectivec atalysis because cyclometalated phenylbenzoxazoles (RhO and IrO)o rp henylbenzothiazoles (IrS)d on ot provide active catalysts.…”

“…Our work follows stereoselective coordination chemistry developed by vonZ elewsky and others using readilya vailable pinene-modified chiral pyridinel igands. [15][16][17][18][19] Specifically,w e reacted 2-phenyl-5,6-(S,S)-pinenopyridine [17] [(S,S)-1]w ith RhCl 3 ·3 H 2 Oo rI rCl 3 ·3 H 2 Oi na3:1e thoxyethanol/water mixture at 125 8Cf or 36 ht oa fford the respective chloro-bridged dimers LL/DD-2 Rh and LL/DD-2 Ir [19] as mixtures of diastereomers (Scheme 2). Consistent with related studies using cyclometalating pinene-derived pryridinel igands, the dinuclear complexes are mainly formed as the homochiral LL-a nd DDdiastereomers, and within the coordination sphere, the kinetically favored trans-arrangement of the pyridine ligands is exclusively observed.…”