Quinone → 3-Acetyl-3a,7a-dihydro-7a-(phenylethynyl)benzofuran-2,5(3H,4H)-dione

Participants

Reaction Conditions

Reaction Steps

Phenylacetylene (1 mL, 9.3 mmole) was placed in dry THF (10 mL) in a dry, 50 mL, 3-necked, round bottomed flask fitted with a mechanical stirrer, thermometer and argon inlet. The solution was cooled to -78° C. and treated with 1.6M n-butyllithium (5.8 mL, 9.3 mmole) in hexane. The reaction was stirred at -78° C. for 30 min, warmed to 0° C., then recooled to -78° C. Benzoquinone (1 g, 9.3 mmole) and dry THF (10 mL) were added, under argon, to a separate 100 mL, 3-necked, round bottomed flask. The mixture was cooled to -78° C. and treated with the lithium phenylacetylide solution prepared above. The flask which contained the lithium phenyacetylide solution was washed with dry THF (10 mL) and the solvent was added to the larger flask. Upon addition of the lithium phenylacetylide, the reaction mixture turned dark blue. The reaction was stirred for 20 min at -78° C. then dry DMPU (18 mL, 0.15 mole) was added. The reaction was stirred for five min before diketene (0.8 mL, 10.2 mmole) in THF (10 mL) was added. The reaction was stirred for 1 hr at -78° C., then allowed to warm to room temperature, stirred overnight and concentrated in vacuo. The residue was treated with water (50 mL) and saturated ammonium chloride (50 mL), acidified with 3N hydrochloric acid, and extracted with CH2Cl2 (4×75 mL). The combined CH2Cl2 extracts were washed with water (50 mL) and brine (2×50 mL), dried over anhydrous sodium sulfate, filtered and concentrated. The residue was dissolved in Et2O (150 mL), and the solution was washed with water (3×50 mL and 1×75 mL) and brine (75 mL), dried over anhydrous sodium sulfate, filtered and concentrated in vacuo. The residue was purified by flash column chromatography (silica gal; eluting with hexane: EtOAc (4:1) to yield 2.4 g (88%) of the title compound. Crystallization from acetone/ethyl acetate gave a white solid, m.p. 168°-171° C. (dec).

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