Asymmetric 1,4-Addition of Organosiloxanes to α,β-Unsaturated Carbonyl Compounds Catalyzed by a Chiral Rhodium Complex

Abstract

Highly enantioselective 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium complex generated from [Rh(cod)(MeCN)(2)]BF(4) and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced enantioselectively into the beta-position of a variety of ketones, esters, and amides. [reaction--see text]

Rhodium‐ and Palladium‐Catalyzed Asymmetric Conjugate Additions

“…With cationic rhodium complexes, organosiloxanes do not require external activator to transmetallate to rhodium. These conditions were applied successfully to the asymmetric variant of this reaction, using (S)-binap as the chiral ligand (Scheme 1.53) [58]. The enantioselectivities observed were very close to those obtained with organoboronic acid, indicating a similar reaction pathway [17,60].…”

Catalytic Organocopper Chemistry from Organosiloxane Reagents

“…[2][3][4] However, the kinetic stability and strong CÀSi bonds of organosilanes have limited the use of organosilane precursors for catalytic generation of other organometallic intermediates. [5] A few reports of rhodium-catalyzed reactivity have appeared, [4,6] but rhodium and palladium processes typically occur in the presence of water, allowing the intermediacy of silanolates which are thought to facilitate transmetalation. [7] Aqueous conditions are possible since these oganometallics are relatively stable to proteolytic decomposition.…”

Rhodium-catalyzed asymmetric addition of aryl- and alkenylboron reagents to electron-deficient olefins

“…The addition of aryltin [26], -silicon [27], and -bismuth [28] reagents to α,β-unsaturated carbonyl compounds catalyzed by a rhodium complex is thought to proceed through a similar catalytic cycle. The addition of arylsilanes has recently been applied to the catalytic asymmetric synthesis [29]. High enantioselectivity has been achieved in the arylation of imines with arylstannanes, which is catalyzed by a rhodium complex coordinated with an axially chiral monodentate phosphine ligand (MOP) [30].…”