The purpose of this article is to give a taste of just how powerful the union between furans and photochemically-generated singlet oxygen is proving to be as a synthetic tool and to suggest that this chemistry is only now really coming of age. In attempting to achieve this goal, its progress from mechanistic curiosity to rapidly maturing applied science will be followed. It will be shown how the field has reached a point where the diversity of product structures attainable is expanding all the time at a tremendous pace and how this expansion allows for a wide variety of important developments from the discovery of new materials and methods for DNA-crosslinking, to the delineation of more sustainable synthetic technologies. To begin with, however, we look briefly at the investigations of the pioneers who laid all the necessary foundations by unravelling the reactions' key characteristics and then we will move on to show how their crucial work has been exploited and applied in increasingly creative ways over the years that have followed.

A highly efficient one-pot transformation of readily accessible furans into 4-hydroxy-2-cyclopentenones in H2O, using singlet oxygen as oxidant, has been developed.

A highly adaptable method targeting the ubiquitous and very important pyrrolizidine and indolizidine scaffolds is presented. The general synthetic utility of the method is underscored by its application to the rapid and easy synthesis of five natural products starting from readily accessible alkylfuran precursors. These unprotected primary furylalkylamines are subjected to photooxygenation conditions, which initiate a complex cascade reaction sequence concluding with the production of high value motifs. This sequence can be tailored to need by varying the choice of both photosensitizer and base additive.

Asymmetric and site-selective formal [3 + 2]-annulations of γ-alkyl-β,γ-unsaturated γ-lactams with α,β-unsaturated aldehydes have been developed. These organocatalysed transformations yield high value enantioenriched bicyclic γ-lactams with up to four new stereocenters (sometimes including a quarternary carbon). The overall transformation starts from simple and readily accessible furans and oversees a rapid, controlled, and dramatic enhancement in 3D complexity.