Synthesis of symmetrical chromeno[2,3-b]chromenes on the basis of о-quinone methides and 1,1-bis(morpholino)ethene

[Figure not available: see fulltext.] The reaction of 1,1-bis(morpholino)ethene with precursors of о-quinone methides derived from Mannich bases of phenols and 2-naphthols provided a series of chromeno[2,3-b]chromenes. The cascade process included a hetero-Diels–Alder reaction between о-quinone methide and ketenaminal, elimination of secondary amine, and [4+2] cycloaddition between о-quinone methide and the chromene intermediate. © 2018, Springer Science+Business Media, LLC, part of Springer Nature