A new strategy to 2-aminochromanes through catalyst-free cascade reaction of 3-trifluoroacetyl-4H-chromenes and 4H-chromene-3-carbaldehydes with cyclic secondary amines is presented. The reaction
proceeds through subsequent 1,4- and 1,2-additions of amine, bimolecular elimination
of trifluoroacetamide or formamide, and 6-exo-trig cyclization. The latter stage is a very rare example of addition of phenols to enamines.
The obtained semicyclic N,O-acetals were applied as useful precursors for the synthesis
of other chromanes.
Key words
chromanes - 4
H-chromenes - cascade reactions - enamines - cyclic secondary amines - N,O-acetals