Carbon Dioxide → 2,3-dihydrospiro[4H-1-benzothiopyran-4,2'[1,3]dioxolane]-6-carboxylic acid

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Reaction Conditions

Reaction Steps

13.58 g (0.047 mol) of the title compound of Step C was added to 150 mL of tetrahydrofuran. The solution was cooled to about -65° C. and 23 mL (0.057 mol) of 2.5 M n-butyllithium in hexane (purchased from Aldrich Chemical Company) was added dropwise while keeping the temperature below -55° C. After stirring under nitrogen for 1 h, excess solid CO2 was added in one portion, and the mixture was stirred overnight while warming to room temperature. 100 mL of hexane was added to the mixture, and it was then filtered. To the solid residue was added 500 mL of water and 400 mL of methylene chloride. The solution was cooled to about 0° C., acidified to pH 1 with concentrated hydrochloric acid, and extracted with methylene chloride (3×400 mL). The resulting solution was dried (MgSO4), filtered, and evaporated to dryness to yield 8.58 g of the title compound of Step D as a solid melting at 186.7° C. (dec). 1H NMR (Me2SO-d6): δ2.2 (m,2H), 3.2 (m,2H), 4.1 (m,4H), 7.2-8.0 (3H), 12.8 (br s,1H).

Provenance & Evidence