Читать книгу Catalytic Asymmetric Synthesis - Группа авторов - Страница 91

In 2005, Jørgensen reported the first enantioselective S_NAr arylation of enolates using chiral phase‐transfer catalysis (Scheme 4.13) [61, 62]. β‐ketoesters could be arylated with activated aryl fluorides using a cinchoninium‐based catalyst. Notably, quaternary carbon centers were formed obviating the potential issue of product racemization.

Scheme 4.12. Enantioselective Mannich reaction using glycine imines.

Scheme 4.13. Enantioselective arylation of 1,3‐dicarbonyl nucleophiles via nucleophilic aromatic substitution.

Source: [61, 62].

In 2014, Maruoka used a similar S_NAr PTC strategy to achieve the enantioselective arylation of glycine imine derivatives (Scheme 4.14) [63]. Here, a chiral ammonium catalyst with a biaryl backbone proved to be optimal. This chemistry was further expanded to use electron neutral and electron‐rich aryl electrophiles, activated as Cr(CO)₃ complexes [64]. Use of a chiral binaphthyl‐derived ammonium catalyst proved to be optimal in this case.

In a further extension of this work, the arylation of oxindoles with activated aryl fluorides was accomplished using a binaphthyl‐derived chiral phosphonium catalyst (Scheme 4.15) [65].

In recent years, the atropselective synthesis of biaryl motifs using chiral phase‐transfer catalysis has garnered increased attention. In 2014, Smith disclosed the first atropselective S_NAr reaction using a dichloropyrimidine electrophile and a thiophenol nucleophile, wherein restricted rotation around the biaryl linkage in the product gives rise to atropisomers (Scheme 4.16) [66]. Moderate to high enantioselectivity is observed using a first‐generation chiral cinchoninium catalyst. Building on this work using the same cinchoninium catalyst and related S_NAr strategy, Gustafson later reported in 2018 the kinetic resolution of pyrolopyrimidines [67].

In 2017, Cai reported a chiral phase‐transfer catalyzed atropselective macrocyclization strategy to access (−)‐pterocarine and (−)‐galeon (Scheme 4.17) [68]. A chiral cinchoninium catalyst was found to catalyze the intramolecular S_NAr reaction of a phenol with an activated aryl fluoride to obtain the desired macrocyclic product with moderate to good enantioselectivity.

Scheme 4.14. Enantioselective arylation of mono‐alkylated glycine imines via nucleophilic aromatic substitution.

Scheme 4.15. Enantioselective arylation of oxindoles via nucleophilic aromatic substitution.

Source: Based on [65].