Chemical synthesis study reveals catalyst-dependent pathways for cyclopropane annulation with thioureas, enabling access to diverse iminodihydrothiophenes and thienobenzazepinediones.
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.
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Daniel et al. (2026) studied this question.
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