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In 2013, the Toste group demonstrated the compatibility of oxopiperidinium salts in conjunction with CAPT catalysis for an enantioselective cross‐dehydrogenative coupling reaction (Scheme 4.46) [155]. Instrumental to this was the development of novel triazole‐containing phosphoric acids, where it was hypothesized that these were engaging in noncovalent interactions with the substrate, leading to high enantioselectivities. A follow‐up mechanistic study focusing on a data‐intensive approach revealed that a π‐stacking interaction between the triazole and the substrate was the primary factor in controlling enantioselectivity [156]. The oxopiperidinium/chiral‐anion system was later utilized in a deracemization reaction of indolines via oxidation to the 3‐H indole scaffold proceeding, and subsequent reduction to the indoline [157]. In 2016, the Toste group reported the asymmetric arylation of benzopyrylium with phenols under phase‐transfer conditions (Scheme 4.47) [158].

Scheme 4.44. Overview of chiral anion phase‐transfer catalyzed bromination and iodination.

Source: Based on [147].

Scheme 4.45. Chiral anion phase‐transfer catalyzed diazenation.

Source: Based on [153].

Scheme 4.46. Asymmetric transformations mediated by oxopiperidinium/chiral anion salts.

Source: Based on [155].

Scheme 4.47. Asymmetric arylation of benzopyrylium with phenols under phase‐transfer conditions.

Source: Based on [158].