Polishing a Diamond in the Rough: “CuH” Catalysis with Silanes

Abstract

The value of a novel chemical transformation is often underappreciated at the time of its discovery. The reasons are doubtlessly manifold, but the "chemical zeitgeist" subtly determines how the new reaction will be received by the chemical community. The enantioselective reduction of carbonyls by copper-catalyzed hydrosilylation was certainly outshone by other asymmetric hydrogenation techniques. A seminal report at an early stage indicated the considerable potential of this catalytic process, yet it was disregarded for more than a decade. A refined mechanistic picture in connection with a plethora of new chiral ligands then led to copper-catalyzed 1,2- as well as 1,4-reductions of carbonyl compounds with excellent levels of enantioselection at high substrate-to-catalyst ratios and even more remarkable substrate-to-ligand ratios. The tide is turning for inexpensive copper catalysts in asymmetric hydride transfer reactions!

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].…”

Asymmetric NaBH4 1,4‐Reduction of C3‐Disubstituted 2‐Propenoates Catalyzed by a Diamidine Cobalt Complex

“…[2,3] Two years later,P faltz and co-workers reported an excellent chiral Co semicorrin catalyst affecting asymmetric 1,4-reduction of a,b-unsaturated carboxylic esters by NaBH 4 ; [4] however,t his development did not result in as ignificant advance in the field. [5] This may be due to the lower atom efficiency,a sw ell as the higher Ef actor,o fN aBH 4 compared with that of the H 2 system. However,h ydrogenation often requires ah igh-pressure-resistance stainlessa utoclave in ad edicated laboratory with specialized techniques for manipulating the air-sensitive catalyst precursor.B yc ontrast, the operational simplicity of NaBH 4 reduction makes experiments very easy,e nabling not only smallscale reactions, but also industrial-scale production.…”

Domino Reactions Involving Catalytic Enantioselective Conjugate Additions

“…Normally, organosilanes serve as the hydride source, as the direct hydride transfer from a stoichiometric copper hydride source such as Stryker's reagent [16] [CuH(PPh 3 )] 6 , or the use of molecular hydrogen, have not yet proved to be successful [17].…”