Application of Copper(II)–Dipyridylphosphine Catalyst in the Asymmetric Hydrosilylation of Simple Ketones in Air

Abstract

Ask a copper: A copper(II) salt/chiral dipyridylphosphine/PhSiH(3) system (see scheme) acts as a very effective and practical catalyst for the asymmetric reduction of heteroaromatic and other types of ketones in air with good-to-excellent enantioselectivities (up to 94%), giving many chiral alcohols that are intermediates for physiologically active compounds. Remarkable temperature effects were observed for some heteroaromatic ketones.

Reduction of Sulfoxides to Sulfides in the Presence of Copper Catalysts

“…Besides molybdenum-, iron-, and zinc-based systems the application of copper can be beneficial. Indeed, the potential of copper catalyst in reduction techniques has been explored in the reduction of various functionalities [46][47][48][49][50][51][52][53][54][55][56][57][58]. However, the catalytic reduction of sulfoxides in the presence of copper has been so far unreported, while the converse process has been studied [59].…”

Copper‐Catalyzed Enantioselective Hydrosilylation of Ketones by Using Monodentate Binaphthophosphepine Ligands

“…It is known from the work of Chan et al [12] and Riant et al [10] that fluoride in the copper precursor is crucial for the generation of the active catalyst. However, for our system we did not observe this effect (Table 1, entry 6).…”

“…However, temperatures below À50 8C and addition of base were required for optimal enantiomeric excess. Noteworthy, a base-free and air-accelerating copper catalyst for the hydrosilylation of carbonyl compounds was presented by Riant and co-workers, [10] which was composed of copper(II) salts such as CuA C H T U N G T R E N N U N G (OAc) 2 [11] or CuF 2 [12] and BINAP. The resulting catalysts typically work at mild temperatures (room temperature to À20 8C), and a remarkably low substrate-to-ligand ratio (S/L up to 50 000 and 100 000) is needed for Xyl-P-Phos [12] for the hydrosilylation of a wide array of aryl alkyl ketones.…”

“…Noteworthy, a base-free and air-accelerating copper catalyst for the hydrosilylation of carbonyl compounds was presented by Riant and co-workers, [10] which was composed of copper(II) salts such as CuA C H T U N G T R E N N U N G (OAc) 2 [11] or CuF 2 [12] and BINAP. The resulting catalysts typically work at mild temperatures (room temperature to À20 8C), and a remarkably low substrate-to-ligand ratio (S/L up to 50 000 and 100 000) is needed for Xyl-P-Phos [12] for the hydrosilylation of a wide array of aryl alkyl ketones. Finally, it should be mentioned that also heterogeneous copper sources (copper-in-charcoal, [13] copper nanoparticles, [14] and copper-aluminum hydrotalcide [15] ) were applied for enantioselective reductions.…”

3,3′-Bipyridine, 4,4′-bis[bis(3,5-dimethylphenyl)phosphino]-2,2′,6,6′-tetramethoxy-, (3R)-; 3,3′-bipyridine, 4,4′-bis[bis(3,5-dimethylphenyl)phosphino]-2,2′,6,6′-tetramethoxy-, (3S)-

“…Reduction of ketones via hydrosilylation could be achieved using copper catalysts containing Xyl-P-Phos and phenylsilane as the hydride donor (eq 2). 7, 8 Asymmetric hydrosilylation of electron-deficient diaryl ketones was performed with moderate to high enantioselectivity (eq 3). Whereas, hydrosilation using nickel catalysts containing Xyl-P-Phos provided moderate enantioselectivity.…”