Asymmetric 1,4-Hydrosilylations of α,β-Unsaturated Esters

Abstract

Complexing catalytic amounts of CuH with a nonracemic JOSIPHOS or SEGPHOS ligand, together with stoichiometric PMHS, leads to exceedingly efficient and highly enantioselective 1,4-reductions of beta,beta-disubstituted enoates and lactones. An unprecedented substrate-to-ligand ratio of 7700:1 for this type of reaction is documented.

Cobalt(II)‐Azabis(oxazoline)‐Catalyzed Conjugate Reduction of α,β‐Unsaturated Carbonyl Compounds

“…[1] Recently, for this purpose a very efficient system based on polyhydroxymethylsilane (PMHS) as stoichiometric reducing agent using chiral Cu(I)/biarylphosphines [2] or Cu(I)/ferrocenyldiphosphines has been introduced. [3] Already in 1989 Pfaltz reported the use of semicorrin ligands such as 3 in combination with CoCl 2 to effect the conjugate reduction of a,b-unsaturated esters and amides by sodium borohydride with high enantioselectivities. [4] Despite the ease of use and the remarkable results obtained by the latter protocol, the limited availability of semicorrins from the chiral pool might have been prohibitive for its wider recognition.…”

Highly Efficient Copper(I) Iodide‐Tolyl‐BINAP‐Catalyzed Asymmetric Conjugate Addition of Methylmagnesium Bromide to α,β‐Unsaturated Esters

“…Currently, most of the reported procedures are based on the use of chiral auxiliaries (enolate alkylations, [2] conjugate additions [3] ), allylic substitutions [4] or substrate control methods.[5] Catalytic asymmetric methods include Negishis Zr-catalyzed carboalumination, [6] Cu-catalyzed conjugate reduction, [7] Lipshutzs Cu-catalyzed hydrosilylation, [8] Ircatalyzed hydrogenation [9] and Feringas Josiphos-catalyzed conjugate addition. [10] Conjugate addition (CA) of MeMgBr to simple and commercially available a,b-unsaturated esters is one of the most direct entries into these structural elements.…”

Katalytische selektive Synthese

“…[131] Die konjugierte Reduktion von 135 gelingt entweder mit einem Rh I -Katalysator und (EtO) 2 MeSiH als Reduktionsmittel [132] oder durch organokatalytische Reduktion mit einem Imidazolidinonkatalysator und einem Hantzsch-Ester als Hydridquelle. [133] ¾hnlich haben Aue und Lipshutz et al [134] kürzlich zwei katalytische Systeme aufgezeigt, um b,b-disubstituierte Enone selektiv in 1,2-und 1,4-Position zu reduzieren (Schema 36 b), basierend auf ihren eigenen früheren Arbeiten [135] und denen von Carreira [136] und Buchwald. [137] Empirisch lässt sich beobachten, dass Ligand 137 die 1,2-Reduktion bevorzugt, während ferrocenylbasierte Liganden dazu neigen, 1,4-Reduktion (138) zu katalysieren; Computerstudien zeigen, dass diese ligandengesteuerte Selektivität ein Ergebnis feiner und komplexer Wechselwirkungen zwischen Substrat, Lçsungsmittel und sterischen Faktoren der Liganden ist.…”