Trifluoroacetic acid → 5-[([4H,5H,6H-cyclopenta[b]thiophen-2-yl]amino)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione

Participants

Reaction Steps

To a solution of tert-butyl N-[4H,5H,6H-cyclopenta[b]thiophen-2-yl]carbamate (480 mg, 2.01 mmol, 1.00 equiv) in 15 mL of DCM was added trifluoroacetic acid (460 mg, 4.03 mmol, 2.00 equiv) at 0° C. After stirring at room temperature for 4 h, the resulting solution was concentrated under vacuum. The pH value was adjusted to 8 with saturated aqueous NaHCO3 solution and extracted with dichloromethane (60 mL×3). Then 5-(ethoxymethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione [prepared by heating 2,2-dimethyl-1,3-dioxane-4,6-dione (580 mg, 4.02 mmol, 2.00 equiv) in 6.0 g of (diethoxymethoxy)ethane at 100° C. for 1 h followed by cooling to room temperature] was added to the above extracts. Drying over sodium sulfate followed by concentration in vacuo afforded 5-[([4H,5H,6H-cyclopenta[b]thiophen-2-yl]amino)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (0.54 g, 92%) as a yellow solid which was used in the next step without further purification.

Provenance & Evidence