A solution of triethylamine (14.8 g, 147 mmol) in dichloromethane (40 mL) was added dropwise under nitrogen to a solution of 2,6-bis(1,1-dimethylethyl)-4-methylselenopyrylium tetrafluoroborate (26.2 g, 73.4 mmol, prepared in Examples 4 and 5 above) and 2,3,4,4-tetrachlorocyclobut-2-en-1-one (15.2 g, 73.4 mmol) in dichloromethane (60 mL), contained in a flask equipped with a condenser and an outlet connected to a gas-washing bottle containing 10% aqueous sodium hydroxide solution; the addition was effected at a rate such that the temperature of the reaction mixture did not exceed 35° C. After the addition had been completed, the reaction mixture was stirred for one hour, then applied to a column packed with silica gel. Elution with dichloromethane, followed by evaporation of the solvent under reduced pressure, provided the crude product which was further purified by trituration with trifluoroethanol for one hour to give 3-[[2,6-bis(1,1,-dimethylethyl)-4H-selenopyran-4-ylidene]methyl]-2,4,4-trichlorocyclobut-2-en-1-one (23 g, 71% yield) as maroon crystals. The structure of this compound was confirmed by mass spectroscopy and by 1H and 13C NMR spectroscopy.
