Chlorosulfonic acid → 2-oxo-2,3-dihydro-1H-indole-5-sulfonyl chloride

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Reaction Steps

1,3-Dihydro-indol-2-one 13 (4.43 g, 33.3 mmol) was added slowly to cold chlorosulfonic acid (9 ml, 135 mmol). The reaction temperature was maintained below 30° C. during the addition. After the addition, the reaction mixture was stirred for 2 h at room temperature, then heated to 68° C. for 1 h, cooled and poured into ice water. The precipitate was washed with water and dried under vacuum to give 2-oxo-2,3-dihydro-1H-indole-5-sulfonyl chloride 14 (5.4 g, 70%). MS m/z 229 [MH]+. 1H NMR, CD3CN 8.91 (S, 1H), 7.90-7.95 (m, 2H), 7.04 (d, J=0.11, 1H), 3.57 (S,1H).

Provenance & Evidence