Trends in the Synthesis and Functionalization of Guaianolides

Guaianolides constitute a large and diverse group of biologically active sesquiterpenes. Guaianolide and seco-guaianolides can also be used as, for example, scaffolds for the development of new active molecules that are readily accessible by synthetic methods. Nevertheless, these lactones often have complex structures that make their synthesis difficult. The aim of this microreview is to provide an overview of the developments in guaianolide synthesis by the two major synthetic strategies: semi-synthesis and total synthesis. Partial and total syntheses of guaianolides are described, with particular emphasis placed on the methods reported in the last decade. The methods discussed include rearrangements, cycloadditions, ring-closing metathesis, the use of transition-metal catalysts, photochemical reactions, and other recently developed techniques as key steps.