Enantioselectivity in visible light-induced, singlet oxygen [2+4] cycloaddition reactions (type II photooxygenations) of 2-pyridones

Abstract

3-Substituted 2-pyridones were enantioselectively (68-90% ee) converted into the respective 3-hydroxypyridine-2,6-diones by a sequence consisting of a template-mediated type II photooxygenation and an acid-catalysed rearrangement.

Mechanistic Insights into Enantioselective CH Photooxygenation of Aldehydes via Enamine Catalysis

“…Amino acids (3-9)a nd Jørgensen catalysts (13,14)w ere obtained commercially.P roline derivatives: 10 and 11, [35] 12, [36] 36 [37] and imidazolidinones: 15, [31a] 46 and 47, [31b] 48-50, [31c] were prepared by known procedures.A mides [37][38][39][40][41][42][43][44][45] were prepared in am anner analogous to the amide 10. [35] Unless otherwisen oted,a ll commercially available starting materials were used directly without further purification.…”

“…[4,8,9] In bsubstitution, the enamine is first oxidized (SET, single-electron transfer)t oe naminyl radical cation, subsequent loss of proton gives a b-enaminyl radical that reacts with the second reactingp artner. [12] Among those reported, Bachs [13] photooxygenation of 2-pyridones (with ee 69-90 %) and Córdovas [14] aoxidation of carbonyl compoundsare of particular importance.T raditional organocatalytic a-oxidationso f aldehydeso rk etones were achieved mainly via enamine catalysis with hazardous oxidants:n itrosobenzene, [15] TEMPO, [16] benzoylp eroxide, [17] oxaziridines [18] or iodosobenzene. tetraphenylporphyrin, TPP), are consideredane ffective and environmental friendly tool for the oxidation of organic compounds.…”

Visible Light‐Induced Salan‐Copper(II)‐Catalyzed Enantioselective Aerobic α‐Hydroxylation of β‐Keto Esters

“…[1] In particular, the reactivity of singlet oxygen ( 1 O 2 ) has been applied to visible light activated asymmetric catalysis in recent years. [2] However, the stereoselectivity control of the enantioselective hydroxylation reaction using photogenerated 1 O 2 as the terminal oxidant still remains a challenge, and work in this field has rarely been reported. [3] Specifically, our group first reported on the chiral phasetransfer catalyzed aerobic transformation using tetraphenylporphyrin (TPP) as the photosensitizer (Scheme 1b), [3a] while Xiao et al reported the asymmetric aerobic oxidation reaction by bifunctional photocatalyst-Ni(II) catalysis (Scheme 1c).…”

“…In order to prevent the insitu generation of the salan-copper(II) from being affected by the water vapor, the air dried by 4 Å molecular sieves was slowly injected via an air pump into the reaction flask, the enantioselectivity was improved to 90% ee ( (Table S3). After further screening of additional solvents, temperatures, and photosensitizers, the best conditions for a-hydroxylation were as follows: L4 with Cu(OTf) 2 as the catalyst and TPP as the photosensitizer in toluene at À15 8C under white CFL irradiation.…”

Controlled Oxygen Release from Pyridone Endoperoxides Promotes Cell Survival under Anoxic Conditions

“…[27][28][29][30][31] The latter provide a scaffold that allows straightforward generation of interesting substitution patterns, whilst their polar nature should enhance solubility in water as compared to e.g. anthracene-derived endoperoxides.…”