Several furyl/thiophenyl/N-methylpyrrolyl cores having aldehyde/ketone/ene-biscarbonyl/diene-biscarbonyl functions at their 2-positions were reacted with diazocarbonyl compounds in the presence of metal catalysts. Between the two possible reaction pathways which may take place either on the 2-substituent of hetaryl or on the core structure, only one of them was dominant for each reaction depending on substituents. Accordingly, in the reaction of thiophene-2-carbaldehyde with diazo compounds we obtained epoxy derivatives. On the other hand, dimethyl diazomalonate and furyl-ene-diketo/N-methylpyrrolyl-ene-diester yielded only novel dihydrofuran derivatives via [1,5]-electrocyclic ring closure. However, the reactions of 2-ene/diene-diester functionalized furans with dimethyl diazomalonate resulted polymethoxycarboxylate-substituted oxo-polyenes chemo-specifically in good yields.