Trifluoroacetic acid → (+)-12-Oxocalanolide A

Beteiligte Stoffe

Reaktionsschritte

Paraldehyde One-Step Reaction: To a stirring solution of chromene 4 (350 mg, 1.0 mmol) and PPTS (250 mg, 1.0 mmol) in 1,2-dichloroethane (2 mL) at ambient temperature under N2 was added 3 mL paraldehyde (22.5 mmol). The resulting mixture was refluxed for 7 h. Then, CF3CO2H (1 mL), an additional equivalent of PPTS and 1 mL of paraldehyde were added; the mixture was refluxed overnight. The reaction mixture was neutralized with saturated aqueous NaHCO3 and extracted with ethyl acetate (50 mL×3). The crude product obtained by evaporation under reduced pressure was washed with hexane. The residue was purified by column chromatography eluting with ethyl acetate/hexane (1:2) to afford 100 mg (27% yield) of chromanone (+)-7 and 30 mg (8% yield) of (+)-7a. Chromanone (+)-7 (10,11-trans-dihydro-4-propyl-6,6,10,11-tetramethyl-2H,6H,12H-benzo[1,2-b:3,4-b′:5,6-b″]tripyran-2,12-dione) obtained by this method was identical with an authentic sample by comparison of TLC, PLC and spectroscopic data.

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