Singlet oxygen photooxygenation of furans

Functionalization of the benzobicyclo[3.2.1]octadiene skeleton via photocatalytic oxygenation of thiophene and furan derivatives: The impact of the type and position of the heteroatom

“…4 Porphyrins proved to be successful in photocatalytic synthesis of several oxygenated derivatives of different types of organic compounds. While free-base porphyrins are well-known sensitizers for production of singlet oxygen, 5,6,7,8,9 metalloporphyrins are much more versatile photocatalysts due to their coordination ability promoting a wider range of oxidation reactions. They can be utilized in autooxidation reactions, hydroxylations or direct oxygen transfer yielding epoxides.…”

“…13 Photocatalytic oxygenation of cycloalkenes 12,13,14 and other unsaturated heteroaromatics 5 was achieved by application of both metalated and free-base porphyrins. 5,12,13,14 These precedents inspired us to study the porphyrin-mediated photocatalytic oxygenation of 2,3-[3,2-b-furo]-6,7-benzobicyclo[3.2.1]octa-2,6-diene (1) (see in Fig. 1), 15 the structure of which represents the basic skeleton of many biologically active and important substances isolated from nature.…”

Singlet oxygen-mediated transformation of furans into aromatic nitrogen-containing polycycles in water

“…The regiochemistry of this opening is irrelevant, since both possibilities later converge, but has been shown as occurring at the most substituted of the two possible positions, as there is evidence, at least when methanol is the solvent, that this is the preferred site for the ozonide opening. [28][29][30] The hydroxyl group derived from the molecule of water could then initiate a ring-opening/closing rearrangement to yield the unusual bis-hemiketal-endoperoxide D. It should be noted here that in recent studies which share certain features with the current cascade reaction sequence, but which furnish entirely different products, we have found and characterized this intermediate. 31 Under aqueous conditions, we propose that the equilibria between B, C and D is sidelined by the collapse of the open chain hydroperoxy ketone C affording the unsaturated keto-aldehyde E, which would in turn be the subject of an attack by the newly introduced amine (E → F).…”

Selective hydrodeoxygenation of 5-hydroxy-2(5H)-furanone to γ-butyrolactone over Pt/mesoporous solid acid bifunctional catalyst

“…This method has been reported by Gollnick, K. 25 A solution consisting of furfural (18.5 ml, 0.223 mol) and rose bengal (0.455 g) in methanol (115 ml) was bubbled oxygen gas and the mixed Scheme 1 Catalytic conversion of furfural into g-butyrolactone.…”