Acetic Acid → 1-(5,7,8,9-Tetrahydro-1H-spiro[cyclohepta[f]indazole-6,2'-[1,3]dioxolan]-1-yl)ethanone

Participants

Reaction Steps

In a 20 L 3 necked flask, N-(3-Methyl-5,7,8,9-tetrahydrospiro[benzo[7]annulene-6,2′-[1,3]dioxolan]-2-yl)acetamide (78) (900 g, 3.27 mol) was dissolved in chloroform (10 L). KOAc (634 g, 6.54 mol), HOAc (382 mL, 6.54 mol), acetic anhydride (655 mL, 6.54 mol), 18-crown-6 (130 g, 523 mmol) and isoamylnitrite (1.30 L, 13.4 mol) were respectively added. The mixture was heated to reflux for about 3 h. Acetic anhydride (900 mL, 9.54 mol) and isoamylnitrite (1.80 L, 13.4 mol) were added and the mixture was heated to reflux overnight. The reaction mixture was cooled to rt and then carefully poured into sat. aq. NaHCO3 (80 L). The pH was carefully adjusted to basic with NaHCO3. The layers were separated and the aq. phase was extracted with DCM (2×15 L). The combined organic layers were concentrated under reduced pressure. tert-Butyl methyl ether (1500 mL) was added and the resulting slurry was stirred for about 1 h. The precipitate was collected by filtration to afford 1-(5,7,8,9-tetrahydro-1H-spiro[cyclohepta[f]indazole-6,2′-[1,3]dioxolan]-1-yl)ethanone (79) (450 g, 48% yield) as a yellow solid. 1H NMR (300 MHz, DMSO): δ 8.38 (s, 1H), 8.05 (s, 1H), 7.72 (s, 1H), 3.95 (m, 2H), 3.82 (m, 2H), 3.16 (s, 2H), 2.96 (m, 2H), 2.64 (s, 3H), 1.84 (m, 2H), 1.62 (m, 2H).

Provenance & Evidence