Kinetic Studies Prove High Catalytic Activity of a Diene–Rhodium Complex in 1,4‐Addition of Phenylboronic Acid to α,β‐Unsaturated Ketones

Abstract

In the 1,4-addition of phenylboronic acid to alpha,beta-unsaturated ketones, [Rh(OH)(cod)]2 has a much higher catalytic activity than [Rh(OH)(binap)]2 (cod = 1,5-cyclooctadiene, binap = 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl). Kinetic studies revealed that the rate-determining transmetalation step in the catalytic cycle has a large rate constant when [Rh(OH)(cod)]2 is used.

Rhodium‐ and Palladium‐Catalyzed Asymmetric Conjugate Additions

“…Using the same methodology, Hayashi and coworkers performed the kinetic analysis of the reaction catalyzed by [Rh(OH)(cod)] 2 (10) (cf. Section 1.5) [25]. Under identical conditions, the rate of the reaction with [Rh(OH)(cod)] 2 (10) was 20-fold faster than with [Rh(OH)((R)-binap)] 2 (9).…”

“…The chiral boron enolate can be further reacted with an electrophile to yield a ketone with a high diastereoselectivity (see Scheme 1.18). Reagents such as bis(pinacolato)diboron (25) [49] and dimethylphenylsilylpinacolatoboron (26) [50,51] have been used to introduce a boron and silyl moiety in Rh-catalyzed addition reactions (cf. Section 1.6; see Scheme 1.59).…”

“…The silyl variant (142) of reagent 140 can also function as a silyl transfer, albeit with only moderate yield due to competitive loss of silane [192]. In addition to aryl and alkenyl groups, bis(pinacolato)diboron (25) and silyl boronic ester 26 can be used in Rh-cat conjugate additions to transfer boron [49] and silyl groups respectively. Thus, the SiMe 2 Ph group can be introduced onto linear and cyclic α,β-unsaturated carbonyl compounds in moderate yields and with high enantioselectivity (Scheme 1.56) [50,51].…”

Phosphate‐Triggered Self‐Assembly of N‐[(Uracil‐5‐yl)methyl]urea: A Minimalistic Urea‐Derived Hydrogelator

“…Further kinetic studies suggested that the transmetallation step was rate limiting and that the dimeric hydroxyrhodium complex was the resting state 6. Interestingly, the use of diene ligands instead of BINAP (e.g., to afford the [{Rh(cod)(OH)} 2 ] precursor; cod=1,5‐cyclooctadiene) yields more active catalysts and the two systems are expected to follow the same mechanism 6b…”

Rhodium‐Catalyzed Asymmetric 1,4‐Additions, in Water at Room Temperature, with In‐Flask Catalyst Recycling

“…Complexation of nonracemic BINAP to rhodium(I) is well known from the work of Miyaura. [9] Hayashi, [10] and Carreira [11] to mediate 1,4-addition reactions of arylboronic acids to enones with high levels of enantiocontrol. [12, 13] Catalyst 1 was prepared via (R)-BINAP derivative 4 by esterification of PQS with known BINAP acid 3 (Scheme 1).…”