posted on 2021-01-05, 15:07authored byFranz-Lucas Haut, Christoph Habiger, Lukas A. Wein, Klaus Wurst, Maren Podewitz, Thomas Magauer
Despite
the many methods available for the synthesis of furans,
few methods remain that allow for the custom-made assembly of fully
substituted furans. Here we report a powerful protocol to rapidly
construct tetrasubstituted, orthogonally functionalized furans under
mild reaction conditions. The developed method involves the regioselective
ring-opening of readily available 2,5-dihydrothiophenes followed by
an oxidative cyclization to provide the heterocycle. The selective
oxidation at sulfur is promoted by N-chlorosuccinimide
as an inexpensive reagent and proceeds at ambient temperature in high
yield within 30 min. The obtained furans serve as exceptionally versatile
intermediates and were shown to participate in a series of valuable
postmodifications. The fate of the initial sulfonium intermediate
was investigated by mechanistic experiments, and computational studies
revealed the existence of an unprecedented Pummerer-type rearrangement.
The potential for organic synthesis is highlighted by the total synthesis
of bisabolene sesquiterpenoids (pleurotins A, B, and D).