(3 + 2) Annulation of Indane-1,3-Dione-Based Spiro Donor–Acceptor Cyclopropanes with Thioureas: Entry to Iminodihydrothiophenes and Thienobenzazepinediones

Abstract Spiro donor–acceptor cyclopropanes (DACs) based on an indane-1,3-dione moiety underwent atypical ring cleavage during their Yb(OTf)3-catalyzed (3 + 2) annulation with thioureas. The gem-diamino tetrahydrothiophene intermediates initially formed in the annulation spontaneously lose ammonia to yield 2-iminodihydrothiophenes. The replacement of Yb(OTf)3 in the transformation by an equimolar amount of AcOH led to benzo[e]thieno[2,3-b]azepine-4,5-diones via intramolecular cyclization of the gem-diamino tetrahydrothiophenes followed by intramolecular ring expansion of the resulting fused azetidine intermediates.