Formation of a Four‐Membered Ring: From a Carbonyl‐Conjugated Alkene

Hehn, Jörg P.; Müller, Christiane; Bach, Thorsten

doi:10.1002/9783527628193.ch6

Cited by 43 publications

(13 citation statements)

References 160 publications

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“…The [2 + 2] photocycloaddition reaction has emerged over the past decades as a powerful tool in organic synthesis and offers a straightforward access to cyclobutanes generating up to four stereogenic centers in a single transformation. Intermolecular [2 + 2] photocycloaddition reactions offer wide flexibility regarding the choice of substrates but frequently suffer from relatively poor regio- and stereocontrol . In contrast to thermal cycloaddition reactions, the intermediate of a [2 + 2] photocycloaddition is short-lived and requires efficient trapping by its reaction partner .…”

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confidence: 99%

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

et al. 2016

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In the presence of a chiral thioxanthone catalyst (10 mol %) the title compounds underwent a clean intermolecular [2 + 2] photocycloaddition with electron-deficient olefins at λ = 419 nm. The reactions not only proceeded with excellent regio- and diastereoselectivity but also delivered the respective cyclobutane products with significant enantiomeric excess (up to 95% ee). Key to the success of the reactions is a two-point hydrogen bonding between quinolone and catalyst enabling efficient energy transfer and high enantioface differentiation. Preliminary work indicated that solar irradiation can be used for this process and that the substrate scope can be further expanded to isoquinolones.

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confidence: 99%

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

et al. 2016

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“…Strained polycyclic scaffolds containing cyclobutane rings are common motifs in many natural and artificial products (Scheme ) that have extensively been used in organic synthesis, materials science, and biochemistry . The photoinduced [2 + 2] cycloaddition reaction of olefins is one of the ideal and straightforward methods to obtain multisubstituted cyclobutanes. Generally, complex intramolecular dienes or superstoichimetric amounts of olefins have to be used to guarantee the efficiency of [2 + 2] cycloaddition reactions.…”

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confidence: 99%

Intermolecular [2 + 2] Cycloaddition of 1,4-Dihydropyridines with Olefins via Energy Transfer

Wang

2017

Org. Lett.

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A highly regio- and diastereoselective visible-light-promoted [2 + 2] cycloaddition between readily available 1,4-dihydropyridines and olefins has been developed. This strategy is operationally simple and atom-economical and enables the construction of strained polysubstituted 2-azabicyclo[4.2.0]octanes with three all-carbon quaternary centers with good functional group tolerance. These products can be easily converted to various structurally unique derivatives. The primary mechanistic studies demonstrated that the reaction proceeds through an energy transfer pathway.

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“…“Forbidden” thermal [2 + 2] cycloreversion leading to two alkenes was also demonstrated in a few cases; ,,− however, considering the Woodward–Hoffmann rules, “allowed” [2 + 2] photocycloreversion represents the method of choice for this transformation . In contrast to photochemical [2 + 2] cycloadditions, which have been accepted as a general synthetic tool toward four-membered carbocyclic rings, , their [2 + 2] photocycloreversions have still been the subject of theoretical or pioneering studies. , One of the reasons is the need for a strong UV light of even shorter wavelength compared to those used in [2 + 2] photocycloaddition procedures. This might be overcome by visible light photocatalysis …”

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Photocatalytic Systems with Flavinium Salts: From Photolyase Models to Synthetic Tool for Cyclobutane Ring Opening

Hartman

Cibulka

2016

Org. Lett.

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Two new photocatalytic systems based on flavinium species formed in situ by protonation of riboflavin-tetraacetate (1) with triflic acid or prepared in advance via alloxazine quaternization are presented as effective tools for oxidative cyclobutane ring [2 + 2] cycloreversion using visible light. The system with 1,3-dimethyl-8-trifluoromethylalloxazinium perchlorate (2c) was found to be superior allowing an acid-free mild procedure, which results in the opening of cyclobutanes with high oxidation potential (up to 2.14 V) and/or with sensitive groups (e.g., furan) without side reactions.

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Formation of a Four‐Membered Ring: From a Carbonyl‐Conjugated Alkene

Cited by 43 publications

References 160 publications

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

Intermolecular [2 + 2] Cycloaddition of 1,4-Dihydropyridines with Olefins via Energy Transfer

Photocatalytic Systems with Flavinium Salts: From Photolyase Models to Synthetic Tool for Cyclobutane Ring Opening

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