New Strategy for the Construction of Epoxy-Bridged Tetrahydropyran Frameworks from Trioxane Precursors: Application to a Concise Synthesis of a Riesling Acetal

Studies on Biomimetic Singlet Oxygen Oxidations: Application to the Synthesis of the Alkaloid Simulenoline

The synthesis of the biologically active alkaloid simulenoline, isolated from the roots of Zanthoxylum simulans, is reported. The natural product was assembled from simple commercial reagents via initial domino Knoevenagel/oxa-6π-electrocyclization followed by a one-pot singlet-oxygen ene-reaction/reduction sequence. New insights of singlet oxygen reactivity with olefinic substrates have been revealed.

Domino Self-Sensitized Photooxygenation of Conjugated Dienones for the Synthesis of 1,2,4-Trioxanes

The photochemical behavior of several dienones was studied under aerobic conditions. 2-Allylidene-1,3-cycloalkanediones prepared via Knoevenagel-type condensation between simple readily available 1,3-dicarbonyl substrates and α,β-unsaturated aldehydes afforded 1,2,4-trioxane derivatives upon UVA irradiation in the presence of oxygen. This domino self-sensitized photooxygenation cascade of conjugated carbonyl systems proceeds stereoselectively and involves the formation of two new oxa-cycles, three new bonds (two C-O), and three stereocenters.

Recent Advances in the Synthesis of Carotenoid-Derived Flavours and Fragrances

Carotenoids are important isoprenoid compounds whose oxidative degradation produces a plethora of smaller derivatives, called apocarotenoids, which possess a range of different chemical structures and biological activities. Among these natural products, compounds having less than 15 carbon atoms in their frameworks are often relevant flavours or fragrances and their manufacturing represents an important economic resource for chemical companies. The strict correlation between stereochemical structure and odour has made the stereospecific synthesis of the latter biological active compounds increasingly important. In this review, the recent advances on the synthesis of the most relevant carotenoid-derived flavours and fragrances are discussed. In particular, the new synthetic methods that have given new and innovative perspectives from a scientific standpoint and the preparative approaches that might possess industrial importance are described thoroughly.