Cascade polyene cyclization reactions are highly efficient and elegant bioinspired transformations that involve simultaneous multiple bond constructions to rapidly generate complex polycyclic molecules. This review summarizes the most prominent work on a variety of cationic and radical cascade cyclizations and their applications in natural product synthesis published between 2014 and 2018.1 Introduction2 Cationic Polyene Cyclizations2.1 Lewis Acid Mediated Polyene Cyclizations2.2 Brønsted Acid Mediated Polyene Cyclizations2.3 Halogen Electrophile Initiated Polyene Cyclizations2.4 Sulfur Electrophile Initiated Polyene Cyclizations2.5 Transition-Metal-Mediated Cationic Polyene Cyclizations3 Radical Polyene Cyclizations3.1 Transition-Metal-Mediated Radical Polyene Cyclizations3.2 Photocatalyst-Mediated Polyene Cyclizations4 Origin of Stereocontrol in Polyene Cyclizations5 Conclusion

Biomimetic total syntheses of resorcinols amorphastilbol, grifolin and grifolic acid have been completed in four steps starting from geraniol and farnesol without the use of phenolic protection. The key steps involve C-acylation of dioxinone-β-keto esters, followed by palladium catalyzed decarboxylative allylic rearrangement and biomimetic aromatization.

(+)-Hongoquercin A and B were synthesized from commercially available trans,trans-farnesol in six and eleven steps, respectively, using dual biomimetic strategies with polyketide aromatization and subsequent polyene functionalization from a common farnesyl-resorcylate intermediate. Key steps involve Pd(0)-catalyzed decarboxylative allylic rearrangement of a dioxinone β,δ-diketo ester to a β,δ-diketo dioxinone, which was readily aromatized into the corresponding resorcylate, and subsequent polyene cyclization via enantioselective protonation or regioselective terminal alkene oxidation and cationic cyclization of enantiomerically enriched epoxide to furnish the tetracyclic natural product cores. Analogues of the hongoquercin were synthesized via halonium-induced polyene cyclizations, and the meroterpenoid could be further functionalized via saponification, hydrolytic decarboxylation, reduction, and amidation reactions.

A ‘green’ and high-yielding electrochemical method for performing tin-free, intermolecular radical reactions (the Giese reaction) has been developed.