Photooxidation von 3‐substituierten Furanen in aprotischen Lösungsmitteln

Abstract

Bei der Photooxidation des Naturstoffes Toonacilin (1) in Benzol ohne Zusatz eines Sensibilisators entstehen die y-Hydroxybutenolide 3 und 4, sowie das bisher nicht beschriebene 0,yEpoxybutanolid 5. Dieser neue Verbindungstyp wird -allerdings nur bei einer mit Methylenblau sensibilisierten Photooxidation in Methylendichlorid unterhalb 0 "C -als Hauptprodukt gebildet, wenn man die Modellverbindung 3-Methylfuran (6) oxidiert. Daneben entstehen das wenig stabile 2,3,4,5-Diepoxy-3-methyltetrahydrofuran (lo), und Citraconsaureanhydrid (11). Photooxidation of 3-Substituted Furans in Aprotic SolventsThe photooxidation of the natural product toonacilin (1) in benzene without addition of any sensitizer yields the y-hydroxybutenolides 3 and 4, and a hitherto unknown B,y-epoxybutanolide 5. This new type of compound is obtained as the main product by photooxidation below 0 "C of the model compound 3-methylfuran (6) in methylene dichloride in the presence of methylene blue, but not in an unsensitized reaction in benzene. Byproducts are 2,3,4,5-diepoxy-3-methyltetrahydrofuran (lo), which is not very stable, and citraconic anhydride (11).

Photooxygenation of Nimonol, a Tetranortriterpenoid from Azadirachta indica. A. Juss.

“…Photooxygenation of furans [ 1 ] and olefins [ 2 ] has drawn considerable attention during the last two decades, as a convenient method for introduction of oxygen at specific sites. A literature survey revealed that reports on the photooxygenation of triterpenoids [ 3 , 4 , 5 , 6 , 7 ] having both furan and olefinic functional groups are scarce.…”

Base-Assisted Regio- and Diastereoselective Conversion of Functionalized Furans to Butenolides Using Singlet Oxygen

“…Another well-known strategy is to use furans as precursors in mild photooxidation reactions that mimic the biogenic process, although stereocontrol in this approach is more difficult . In this paper, we report a base-assisted, regio- and diastereoselective conversion of 3-hydroxyacrylate furans to β-substituted γ-hydroxybutenolides using singlet oxygen.…”

“…Although 3-hydroxyacrylate furans have not been used prior to this study in singlet oxygen oxidation reactions for synthesizing functionalized butenolides, it is well recognized that 3-alkyl- or 3-hydroxyalkylfurans are useful synthons for accessing butenolides with regioselectivity in a base-dependent manner 4d. This approach has been applied in a number of total syntheses of bioactive γ-hydroxybutenolide natural products such as cacospongionolides and cladocorans .…”

Dactyltronic Acids from the Sponge Dactylospongia elegans

“…To check the chemical feasibility of these hypotheses we subjected compounds 1,4,5, and 6 to mild basic treatment2. In the cases of illimaquinone [4}, dactylospongenones A-D [51, and dictyoceratin C [6], neither 3 nor any of the other metabolites reported in Q) = Sesquiterpene nucleus simple furans to butenolides is well known (15)(16)(17), and may be related to the cooccurrence of fiiran rings in different oxidation states (i.e., fiiran, -lactone, and tetronic acid) in linear terpene metabolites. This has frequently been observed in sponges, especially those of the genus Ircinia (18).…”