To a stirred solution of 3,4-di-tert-butylthiophene 1-oxide (100 mg, 0.47 mmol) and a trapping reagent (diene, alkene, or alkyne; 4.7 mmol) in CH 2 Cl 2 (ca. 0.5 mL) was added 58 µL (0.47 mmol) of dimethyl acetylenedicarboxylate at room temperature. The resulting reaction mixture was stirred for 0.5 h and evaporated under reduced pressure at room temperature. The residue was purified by silica-gel column chromatography (dimethyl 4,5-di-tert-butylphthalate (3) was eluted with CH 2 Cl 2 , and trapping product was usually eluted by ethyl acetate or methanol) and then by gel permeation chromatography, pot-to-pot distillation, or recrystallization. Spectroscopic Data for New Compounds and a Few Selected Compounds Compound 4eSO