Chiral Cyclopentadienyl Iridium(III) Complexes Promote Enantioselective Cycloisomerizations Giving Fused Cyclopropanes

Abstract

The cyclopentadienyl (Cp) group is a very important ligand for many transition-metal complexes which have been applied in catalysis. The availability of chiral cyclopentadienyl ligands (Cp(x) ) lags behind other ligand classes, thus hampering the investigation of enantioselective processes. We report a library of chiral Cp(x) Ir(III) complexes equipped with an atropchiral Cp scaffold. A robust complexation procedure reliably provides Cp(x) Ir(III) complexes with tunable counterions. In a proof-of-concept application, the iodide-bearing members are shown to be highly selective for enyne cycloisomerization reactions. The dehydropiperidine-fused cyclopropane products are formed in good yields and enantioselectivities.

Enantioselective Tandem Cyclization of Alkyne‐Tethered Indoles Using Cooperative Silver(I)/Chiral Phosphoric Acid Catalysis

“…To address this problem, both well-defined large chiral ligands [5] and the use of chiral counter anions have been studied with some success. [6] Some of these reactions were rendered enantioselective by using other carbophilic catalysts, such as iridium, [7] platinum, [5c,8] palladium, [9] and copper. [10] However, these strategies can only be applied to a limited number of transformations.…”

Chiral Cyclopentadienyl Iridium(III) Complexes Promote Enantioselective Cycloisomerizations Giving Fused Cyclopropanes

“…1,1-disubstitued olefins (R 1 = H) react more selectively with methoxy-substituted complex 3d (Table 3, entries [17][18][19]. [9] In analogy to related reactions with Au and Pt catalysts, [13a, 16c,d] the following catalytic cycle is proposed (Scheme 2). Related substrates that have the NTs group replaced by an oxygen atom or am alonate group react very sluggishly.T he absolute configuration of the cyclopropane products was unambiguously established by X-ray crystallographic analysis of 5g to be (S,S,S).…”

Asymmetric Alkenyl C−H Functionalization by CpxRhIII forms 2H‐Pyrrol‐2‐ones through [4+1]‐Annulation of Acryl Amides and Allenes

“…Different chiral cyclopentadienyl ligands were then surveyed. Catalyst ( R )‐ Rh2 , which has bulkier O i Pr groups, showed almost the same selectivity as ( R )‐ Rh1 (entry 8), while TMS‐containing trisubstituted complex ( R )‐ Rh3 was less selective (entry 9) . Notably, the i Pr‐bearing trisubstituted Cp x Rh III complex ( R )‐ Rh4 in combination with AgOAc significantly improved the yield as well as the asymmetric induction, delivering 3 aa in 74 % yield and 91.5:8.5 er (entry 10).…”