Benzopyrans. Part 41. Reactions of 2-(2-dimethylaminovinyl)-1-benzopyran-4-ones with various dienophiles

Dienamine 1 with N-phenylmaleimide and chromenone 14 as well as 15 produces , through initial [4+2]cycloaddition, xanthenones 10 and 18, respectively. Initial Michael addition of 1 to chromenones 14 and 16, and dimethyl acetyl enedicarboxylate (DMAD), triggers the formation of xanthenone 19, 4-azaxant henone 26 and substituted fumarate 49, respectively. Initial [2+2]cycloaddu cts of dienamines 1-3 with electrophilic acetylenes always undergo further transformations. Thus, 1 with DMAD, dibenzoylacetylene and ethyl propiolate (EP) ultimately gives xanthenones 33, 34 and 37, respectively, the latter being admixed with flavone 43. Enamine 2, cyclisable to xanthenone 11, give s 33 and 35 with DMAD, and 37 and 44 with EP. Reaction of 3 with DMAD affor ds 36 exclusively.