From simple furans to complex nitrogen-bearing aromatic polycycles by means of a flexible and general reaction sequence initiated by singlet oxygen.

All-in-one: A new and general one-pot reaction sequence initiated by singlet oxygen that transforms simple furan substrates into complex nitrogen-bearing aromatic polycycles having all the structural features of a number of important natural products (for example, the erythrina alkaloids; see scheme, RB = rose Bengal) is reported. The reaction sequence itself uses mild conditions and has wide functional group tolerance.

Flexible approach to stemona alkaloids: total syntheses of (-)-stemospironine and three new diastereoisomeric analogs.

Total syntheses of (-)-stemospironine and three new diastereoisomeric analogs have been completed through a flexible strategy devised for Stemona alkaloids. The azabicycle 7 is the pivotal intermediate, from which the sequence splits according to each particular target. The most remarkable differential feature for stemospironine is the installation of the spiranic γ-lactone through an intramolecular Horner-Wadsworth-Emmons olefination.