A large variety of publications have emerged in 2020 involving O- and S-six-membered
ring systems. Special emphasis is given to the large number of reviews that
have been published during this year, perhaps because the pandemic situation caused
by COVID-19 forced scientists around the world to leave their work in the laboratory
and concentrate their efforts on the compilation of reviews. Hereinafter, we provide a personal overview of the most important develop
This chapter is dedicated to the synthesis of O- and S-6-membered heterocycles, covering
the literature published during 2019. Highlights include the most interesting chemistry
dedicated of these heterocyclic ring systems, from our personal point of view,
with special emphasis to the synthesis of natural oxygen derivatives.
Reviews on the isolation, biological properties, biosynthesis, and total synthesis of
benzannulated spiroketal natural products (19OBC8272) and of diterpene pyran-
2-ones (19OBC8943), on the natural occurrence, pharmacological properties, and
structureeactivity relationships of quassinoids, a kind of triterpenoid bearing a tetrahydropyran
bridge (19CPB654), on the biosynthesis of Monascus azaphilone pigment
congeners containing chromene frameworks (19NPR561), and on naturally occurring
3-aryl-4H-chromen-4-ones isolated after 2012 (19NPR1156), have appeared.
