ChemInform Abstract: Iron‐ and Cobalt‐Catalyzed Asymmetric Hydrosilylation of Ketones and Enones with Bis(oxazolinylphenyl)amine Ligands.

Cytochrome P450 CYP199A4 from Rhodopseudomonas palustris Catalyzes Heteroatom Dealkylations, Sulfoxidation, and Amide and Cyclic Hemiacetal Formation

“…The enantiomers were identified based upon comparison of their elution order and optical rotation with literature reports. 31,32 However, these assignments were apparently based upon catalyst specificity and so The racemic mixtures of the 4-alkylthiobenzoic acids were generated by reacting them with hydrogen peroxide before derivatisation to the methyl esters.…”

Iron-Catalyzed Homogeneous Hydrosilylation of Ketones and Aldehydes: Advances and Mechanistic Perspective

“…Regarding the hydrosilanes employed, the activated rather hazardous (EtO)3SiH7 appears in the 739 literature as the most frequently used in optimized reaction conditions so far (Table 1, entries 18, 740 20, 25, 31-33), followed by the expensive PhSiH3 (Table 1, reported iron-based catalytic systems (Table 1, entries 17,21,27,28,30,34). 744…”

“…Continuing their work on hydrosilylation catalyzed by a combination of iron(II) acetate and polidentate nitrogen-based ligands, 22 the group of Nishiyama focused on the use of chiral bis(oxazolinylphenyl)amine "Bopa" ligands (Scheme 3) with the ability to induce asymmetry in the reduced product. 28 In this case, the use of cobalt(II) acetate instead of the iron precursor was also explored. After optimization experiments on the hydrosilylation of methyl 4-phenylphenyl ketone, probing different Bopa ligands, the bis(benzyl)-and bis(phenyl)-substituted ligands were 205 found to provide the best conversions and enantioselectivities for the iron-and the cobalt-catalyzed 206 reactions, respectively.…”

“…Using the optimized catalytic systems (Scheme 3), a wide range of methyl 207 aryl ketones were conveniently reduced to their corresponding alcohols (with R absolute 208 configuration in all cases), with excellent yields and moderate to good enantioselectivities, being 209 notably higher for the cobalt-based catalytic mixture. 210 Although iron and cobalt chlorides had previously demonstrated to be inefficient as the metal 214 precursor for this kind of catalytic settings, 22,28 the combination of the iron(III) chloride complex 215 (Bopa-dpm)FeCl2 (Scheme 4) with zinc powder allowed to convert a variety of ketones into alcohols with good conversions and enantioselectivities. 29 The most remarkable aspect of this new catalytic system is that, under similar reaction conditions (Scheme 4), the resulting alcohols show S absolute configuration, in contrast to the products of the previous method.…”

“…29 The most remarkable aspect of this new catalytic system is that, under similar reaction conditions (Scheme 4), the resulting alcohols show S absolute configuration, in contrast to the products of the previous method. 28,29 It is worth noting that magnetic susceptibility measurements using the Evans method 30 of (Bopa-dpm)FeCl2 in solution, suggested that the addition of zinc powder causes the reduction of the metal center from wide range of ketones with remarkable high enantiomeric excesses and excellent conversions. 32 Reaction conditions were optimized for the use of a 5 mol% of iron catalyst and 2 equivalents of (EtO)2MeSiH in toluene solution, adding the silane at -78 ºC and then allowing the mixture to 242 warm up to room temperature (Scheme 5).…”