Concise Synthesis of Thiazolo[4,5-b]indoles via Ring Switch/Cyclization Sequences

The unexpected reactions of indoline hemiaminals affords 2,5-diaryl-4-hydroxythiazolines through a thioamidation/ring switch sequence. The key to success of this transformation is to use a thioamide as a thiazoline precursor under transient tautomeric control. This transformation features mild reaction conditions and good yields with broad functional group tolerance (17 examples, up to 99 % yield). Further transformations of the thiazolines provide a direct entry to dihydrothiazolo[4,5-b]indoles and thiazolo[4,5-b]indoles.