Access to Multisubstituted Furan-3-carbothioates via Cascade Annulation of α‑Oxo Ketene Dithioacetals with Isoindoline-1,3-dione-Derived Propargyl Alcohols

A Brønsted
acid-promoted, unprecedented formal (3 + 2) annulation
strategy for the synthesis of multisubstituted furan-3-carbothioates
is reported. This transformation represents the first regioselective
annulation of α-oxo ketene dithio-acetals as 1,3-bis-nucleophiles
in a cascade manner. The choice of isoindoline-1,3-dione-derived propargyl
alcohols is crucial to the uncommon annulation mode between an alkyne-type
bis-electrophile and a 1,3-bis-nucleophile under metal-free conditions.
The scale-up of the synthesis and several interesting transformations
of an as-synthesized product were further investigated. A Nazarov-like
cyclization is proposed for the ring-closure process according to
the experimental observations.