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The Nazarov 4π‐conrotatory electrocyclization reaction is a useful and powerful method for the construction of cyclopentanones. Rueping reported the first Nazarov cyclization reaction catalyzed by phosphoramide 14 in 2007 [110]. Tius reported a Nazaro cyclization that generated a vicinal all‐carbon quaternary stereocenter using chiral phosphoramide 14 as the catalyst [111]. Enantioselective Nazarov reactions were limited to activated substrates or cyclic ketones. List reported a Nazarov reaction of simple, acyclic, aliphatic‐substituted divinyl ketones using confined IDPi 11l to furnish 2‐methylene cyclopentenone with 92–99% ee (Scheme 2.56) [112].

Scheme 2.54. [4+3] Cycloannulation reaction between ortho‐quinone methides and carbonyl ylides.

Scheme 2.55. [4+3] Cycloaddition reaction between furans and oxa‐allyl cations.

Source: Based on [109].

Chan reported a dehydrative Nazarov‐type electrocyclization reaction of electron‐rich aryl‐ and 2‐thienyl‐β‐amino‐2‐en‐1‐ols using 14e. The 4π conrotatory electrocyclization gave a wide variety of 1H‐indenes and 4H‐cyclopenta[b]‐thiophenes (Scheme 2.57) [113].

Tu reported a tandem Nazarov cyclization semipinacol rearrangement reaction using unactivated substrates to furnish spiro[4.4]nonane‐1,6‐diones using chiral phosphoramide 14f (Scheme 2.58) [114].

Scheme 2.56. Nazarov reaction of acyclic divinyl ketones.

Source: Based on [112].

Scheme 2.57. Nazarov‐type electrocyclization.

Source: Based on [113].

Scheme 2.58. Tandem Nazarov cyclization semipinacol rearrangement reaction.

Source: Based on [114].