Catalytic Cycloisomerization-Vinylogous Nazarov Reaction Sequence of Enyne Diesters Derived from 2-Propargyloxyarylaldehydes

Enyne diesters derived from 2-propargyloxyarylaldehydes undergo enyne metathesis type cycloisomerization reaction followed by vinylogous Nazarov reaction when treated with 10 mol % In(OTf)₃ in HFIP to generate functionalized indeno[2,1-c]chromenes. This reaction sequence exhibits broad substrate scope and provides direct access to a wide variety of indeno-chromenes and its thia- and aza-analogues in good yields. The methodology can be extended for the synthesis of benzothienocyclopenta[1,2-c]chromene and chromenocyclopenta[1,2-b]indole derivatives as well as estrone-based hybrid molecules.