(±)-Rubioncolin D, a pair of enantiomeric naphthohydroquinone dimers from Rubia oncotricha

•A pair of novel enantiomeric naphthohydroquinone dimers were isolated from Rubia oncotricha.•(±)-Rubioncolin D (1) shared an unprecedented spiro[4.5] carbon core.•The absolute configurations were determined by the calculated ECD spectra.