six heteroaromatic compounds, ethyl-/methyl- and dimethylfuranones, thiophenones, and cyclopentenones, was synthesized and condensed with a methyl methylpropionate substituted pyrrole, yielding the “right” half of open-chain tetrapyrroles. These compounds serve as light-inducible chromophores in the plant photoreceptor phytochrome. Three-dimensional structure analysis of the 10-oxapyrromethen-1-one