Electrophilic indoles having two electron-withdrawing groups undergo nucleophilic attack at C2 and electrophilic functionalization at C3. This is the first enantioselective formal [3+2] cycloaddition using electrophilic indoles. The PyBidine/Cu catalyst smoothly promoted highly enantio- and exo'-selective [3+2] cycloaddition using imino esters and 3-nitroindoles. This reaction provides a method for the preparation of diverse and complex chiral pyrroloindoline compounds.

TOP class: The first efficient catalytic asymmetric coupling reaction of indoles with isatin-derived nitroalkenes was accomplished by using a complex consisting of a chiral imidazoline aminophenol ligand (1; see scheme) and Cu(OTf)(2). Biological activity of the newly formed chiral 3,3'-bisindoles was also confirmed in a Wnt signaling inhibitory assay.

A bis(imidazolidine)pyridine (PyBidine)-Cu(OTf)2 complex catalyzing the endo-selective [3+2] cycloaddition of nitroalkenes with imino esters was applied to the reaction of methyleneindolinones with imino esters to afford spiro[pyrrolidin-3,3'-oxindole]s in up to 98 % ee. X-ray crystallographic analysis of the PyBidine-Cu(OTf)2 complex and DFT calculations suggested that an intermediate Cu enolate of the imino ester reacts with nitroalkenes or methyleneindolinones, which are activated by NH-hydrogen bonding with the PyBidine-Cu(OTf)2 catalyst.

The first catalytic asymmetric exo′‐selective [3+2] cycloaddition of methyleneindolinones with iminoesters was achieved for construction of novel diastereomers of spiro[pyrrolidin‐3,3′‐oxindole]. By using the imidazoline–aminophenol‐ligand complex [Ni(OAc)2–(L1)], the reaction proceeds in the stepwise Michael–Mannich reaction to give the exo′ adducts as stable isomers (see scheme).

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The catalytic asymmetric Friedel-Crafts/protonation of indoles and pyrroles with α-substituted nitroalkenes to give the corresponding adducts in a highly anti-selective manner was achieved by an imidazoline-aminophenol (L2)-Cu complex. The anti-adducts could be successfully transformed to biochemically important α-substituted β-heteroarylalkylamines.

Indol an Indol: Die erste effiziente katalytische asymmetrische Kupplung von Indolen mit Isatin‐Nitroalkenen gelang durch Einsatz eines Komplexes aus dem chiralen Imidazolin‐Aminophenol‐Ligand 1 (siehe Schema) und Cu(OTf)2. Die biologische Aktivität der so erhaltenen chiralen 3,3′‐Bisindole wurde in einem Inhibitionsassay des Wnt‐Signalwegs bestätigt.

Chiral ligand: The [PyBidine–Cu(OTf)2] (Tf=trifluoromethanesulfonate) complex catalyzed the asymmetric Mannich reaction of sulfonyl imines and iminoesters to give the products in a high syn‐selective manner. For both 4‐toluene (Ts)‐ and 4‐nitrophenylsulfonyl (Ns)‐imines, the syn‐adducts were obtained in up to 99 % ee (see scheme).