5-(2-Methylthio-4-methyl-5-pyrimidinyl)-2,4-pentadiynyl-sorbate 2 was synthesized and characterized. It had two conjugating systems, which made its 5J and 6J H-1-C-13 correlating signals be obtained in gHMBC spectra. Intramolecular Diels-Alder reaction tandem dehydroaromatization of diene-diyne 2 under heating and irradiating resulted in formation of benzolactone. The reaction underwent the two steps: thermochemistry and photochemistry. The intermediate was confirmed using C-60 as an intermediate catcher. This reaction represents a rare example of intramolecular Diels-Alder reaction tandem dehydroaromatization of diene-diyne under mild conditions without catalyst and oxidant.