Asymmetric induction by chiral silicon groups

B(C6F5)3‐Catalyzed Reduction of Ketones and Imines Using Silicon‐Stereogenic Silanes: Stereoinduction by Single‐Point Binding

“…Purification by flash column chromatography on silica gel (mixtures of cyclohexane/tert-butyl methyl ether) affords the analytically pure products as colorless, highly viscous oils or solids. Modified Two-Step Procedure for the Preparation of rac-40 [33] rac-Isopropylmethoxymethylphenylsilane: To a solution of dimethoxymethylsilane (3.65 g, 20.0 mmol, 1.00 equiv.) in THF (150 mL) was added iPrMgCl (17.4 mL of a 2.30  solution in Et 2 O, 40.0 mmol, 2.00 equiv.)…”

“…General Information: B(C 6 F 5 ) 3 (1), [25] rac-8 and ( Si R)-8, [14b] ketones 15, [26] 16 [27] and 26, [28] silanes 31 [29] and 32, [30] imines (E/Z)-37 [31] and 42, [32] silicon-stereogenic silanes rac-39 [33] and rac-41 [34] were prepared according to known procedures. All reactions were performed in flame-dried Schlenk tubes under a static pressure of argon using conventional Schlenk technique or a glovebox.…”

Conclusive Evidence for an SN2‐Si Mechanism in the B(C6F5)3‐Catalyzed Hydrosilylation of Carbonyl Compounds: Implications for the Related Hydrogenation

“…We first assessed silanes rac ‐ 2 a – d in the hydrosilylation of acetophenone ( 4 ) in the presence of catalytic amounts of catalyst 1 (5.0 mol %) in order to identify a sufficiently reactive stereogenic silane ( 4 → rac ‐ 6 , Scheme ). It is interesting to note that, without exception, all silanes decorated with a t Bu group—cyclic rac ‐ 2 a ,21a cyclic and strained rac ‐ 2 c ,21b and acyclic rac ‐ 2 d 21c—were to completely unreactive. In contrast, cyclic rac ‐ 2 b 15b equipped with an i Pr group readily delivered the desired product rac ‐ 6 b in good yield and with notable diastereoinduction (vide infra).…”

Schlüssiger Nachweis eines SN2‐Si‐Mechanismus in der B(C6F5)3‐ katalysierten Hydrosilylierung von Carbonylverbindungen: Einsichten in die verwandte Hydrierung

“…Um ein hinreichend reaktives chirales Silan zu identifizieren, überprüften wir zunächst die Silane rac ‐ 2 a – d auf ihre Eignung für die Hydrosilylierung von Acetophenon ( 4 ) in Gegenwart katalytischer Mengen (5.0 Mol‐%) des Katalysators 1 ( 4 → rac ‐ 6 , Schema ). Alle t Bu‐substituierten Silane – cyclisches rac ‐ 2 a ,21a cyclisches und gespanntes rac ‐ 2 c 21b sowie acyclisches rac ‐ 2 d 21c – erwiesen sich als völlig unreaktiv. Dagegen lieferte cyclisches rac ‐ 2 b 15b mit einer i Pr‐Gruppe das gewünschte Reaktionsprodukt rac ‐ 6 b in guter Ausbeute an isoliertem Produkt und mit bemerkenswerter Diastereokontrolle (siehe unten).…”