Synthesis of the A-F Fragment of the Pacific Ciguatoxin CTX3C by Iterative Ring-Closing Metathesis and Tsuji-Trost Allylation.

The fully functionalized A-F fragment of the Pacific ciguatoxin CTX3C has been synthesized from a derivative of D-glucal, which serves as the B-ring. Rings A and C were introduced to either side of ring B by ring-closing diene and enyne metathesis (RCM). The seven-membered D-ring and eight-membered E-ring were assembled by iterative use of a six-step reaction sequence in which RCM was used for ring construction and Tsuji-Trost allylation was employed for subsequent stereoselective functionalization. The nine-membered F-ring was formed by use of an RCM reaction and bears the functionality required for attachment of the I-M fragment and subsequent closure of rings G and H.

One-Pot Transformation of Simple Furans into Octahydroindole Scaffolds.

A highly efficient and general singlet-oxygen-initiated one-pot transformation of readily accessible furans into octahydroindole scaffolds has been developed.

Photooxygenation of Furylalkylamines: Easy Access to Pyrrolizidine and Indolizidine Scaffolds.

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.

One-pot transformation of simple furans into 4-hydroxy-2-cyclopentenones in water.

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.

Singlet-Oxygen-Mediated Synthesis of Pandanusine A and Pandalizine C and Structural Revision of Pandanusine B.

The first synthesis of racemic pandanusines A and B and pandalizine C, isolated from Pandanus amaryllifolius, is reported. The key synthetic step is an efficient tandem reaction sequence initiated by the photooxidation of an easily prepared furylalkylamine precursor. In this reaction sequence, methylene blue plays a dual catalytic role of photosensitizer and redox catalyst, first in generating singlet oxygen and second in facilitating a triplet oxygen reaction. Through the synthesis of pandanusine B, the proposed structure has been revised.

The Power of Triplet and Singlet Oxygen in Synthesis: 2-Oxindoles, 3-Hydroxy-2-oxindoles, and Isatins from Furans.

A straightforward synthesis of substituted 2-oxindoles, 3-hydroxy-2-oxindoles, and isatins has been developed. Easily accessible furans were transformed into tetrahydropyranopyrrolones by a singlet oxygen initiated cascade reaction sequence. An acid-catalyzed rearrangement, followed by aromatization, gave access to a variety of 2-oxindole motifs, which were oxidized to 3-hydroxy-2-oxindoles or isatins using methylene blue as a radical initiator and molecular oxygen as a terminal oxidant.

Asymmetric and Site-Selective [3 + 2]-Annulations for the Synthesis of High-Value Bicyclic Lactams.

Asymmetric and site-selective formal [3 + 2]-annulations of γ-alkyl-ß,γ-unsaturated γ-lactams with α,ß-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.

Singlet oxygen-mediated synthesis of bis-spiroketals found in azaspiracids.

Conversion of a simple furan into the ABCD-ring skeleton of the azaspiracids via a singlet oxygen-initiated one-pot process has been accomplished.

Furans and singlet oxygen--why there is more to come from this powerful partnership.

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.