Chiral Olefins as Steering Ligands:  Syntheses of C₁-Symmetric Dibenzo[a,e]cyclooctenes (^Rdbcot)

Abstract

A simple three-step synthesis of chiral dibenzo[a,e]cyclooctenes (dbcot) starting from commercially available dibenzosuberenone was developed. These compounds give highly stable and robust rhodium(I) and iridium(I) diene complexes of the type [M(Rdbcot)(L1)(L2)] (M = Rh, Ir; L1, L2 = MeCN, Cl, diamine, chloride). The complex [Rh((R)-Phdbcot)((R)-(+)-1,1‘-binaphthyl-2,2‘-diamine)]+OTf- could be obtained in enantiomerically pure form and catalyzes the enantioselective 1,2-addition of PhB(OH)2 to α,β-unsaturated ketones with good activity and acceptable enantiomeric excess (62%). The iridium complex [Ir(Phdbcot)(MeCN)2]+OTf- catalyzes the hydrogenation of dimethylitaconate with good activity, while the rhodium complexes are almost inactive. Likewise, the complex [Ir(Phdbcot)(H2NCH2CH2NH2)]+OTf- serves as a rather efficient catalyst precursor with an activity 4 orders of magnitude higher than for the analogous rhodium complex. These experiments further establish the use of dienes as steering ligands in catalysis.

Chiral Olefins as Steering Ligands in Asymmetric Catalysis

“…Grützmacher and co-workers employed, however, an alternative approach: an organometallic method in which the enantiomers were resolved by formation of diastereomeric complexes of the racemic diene followed by the addition of a chiral diamine and subsequent crystallization (Scheme 17). [57] The synthesis of 76 started from commercially available dibenzosuberone (71). Ring expansion by treatment with TMSCHN 2 , subsequent addition of a phenylcerium reagent, and dehydration provided 73.…”

Rhodium‐ and Palladium‐Catalyzed Asymmetric Conjugate Additions

“…Since the first application of chiral (S,S)-2,5-dibenzylbicyclo[2.2.1]heptadiene ((S,S)-L27b) in the addition of phenylboronic acid to cyclohex-2-enone by Hayashi and coworkers [93], a variety of bicyclic diene scaffolds [94][95][96][97][98][99][100][101][102][103][104] has been successfully applied (Scheme 1.15). Independently, Carriera and coworkers reported the application of a chiral diene for Ir-catalyzed allylic substitution [105].…”

“…The Ph-dbcot (L37) [98] and 1,5-Ph-cod (L38) [97] are achiral dienes, but when coordinated to Rh they become conformationally locked, which leads to a pair of enantiomers that can be subsequently resolved such that, ultimately, enantiomerically pure cationic rhodium complexes [Rh 4 ) gave high ee-values at low conversion. However, the enantioselectivity was eroded at higher conversions due to the conformational instability of ligand L38 of the complex [98].…”

Chiral Phosphane Alkenes (PALs): Simple Synthesis, Applications in Catalysis, and Functional Hemilability

“…[2] Chiral ligands A-D in which the stereogenic centers result from asymmetric substitution of a coordinated alkene (Scheme 1) were recently introduced by Hayashi [3] and Carreira [4] and their co-workers as well as by our group [5] and proved to be effective in a wide variety of hoAbstract: A simple synthesis of a chiral phosphane alkene (PAL) involves: 1) palladium-catalyzed Suzuki coupling of 10-bromo-5H-dibenzoA C…”