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.

We report the eco-friendly synthesis of fused pyrano[2,3-b]pyrans via ammonium acetate-mediated formal oxa-[3 + 3]-cycloaddition of 4H-chromene-3-carbaldehydes and cyclic 1,3-dicarbonyl compounds.

We have studied the [3 + 2]-cycloaddition of various N,N-cyclic azomethine imines to 3-nitrobenzofurans.

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Reaction of 3-formylchromone with cyclic secondary amines in methanol results in (E)-2-methoxy-3-(R2N-methylene)chroman-4-ones, while use of ethanol leads to (E)-2-morpholino-3-(morpholino­methylene)chroman-4-one or enaminoketones as dihydropyran ring-opening products. The solubility of the formed products in alcoholic media is postulated to be a key factor that determines the reaction pathway.

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The reactions of 2-perfluoroacyl-1H-benzo[f]chromenes and 6,7-dimethyl-3-trifluoroacetyl-4Hchromene with primary aliphatic amines and ammonia afforded a series of enamino ketones containing a (2-hydroxynaphthalen-1-yl)methyl or 2-hydroxybenzyl substituent in the α-position with respect to the carbonyl group. These reactions involved opening of the pyran ring, which followed aza-Michael addition as the initial step. The obtained enamino ketones were found to exist in DMSO solution as single E isomers.

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