N[C:2]1[CH:13]=[CH:12][C:5]2[O:6][C:7]3([C:10](=[O:11])[C:4]=2[CH:3]=1)[CH2:9][CH2:8]3.N([O-])=O.[Na+].C(=O)([O-])O.[Na+].[C-:23]#[N:24].[K+]>Cl.C(OCC)(=O)C.C1(C)C=CC=CC=1>[C:23]([C:2]1[CH:13]=[CH:12][C:5]2[O:6][C:7]3([C:10](=[O:11])[C:4]=2[CH:3]=1)[CH2:9][CH2:8]3)#[N:24]5-Aminospiro[benzo[b]furan-2(3H),1'-cyclopropane]-3-one (1.75 g.) was dissolved in conc. HCl (2.5 ml.) and ice-water (20 ml.), and to the solution was added dropwise 2 ml of aqueous solution of sodium nitrite (0.7 g.) under ice-cooling. After stirring for one hour and adding toluene (5 ml.), the solution was neutralized with sodium hydrogen carbonate at -20° C. To 18 ml of another aqueous solution of cuprous cyanide prepared from cuprous chloride (2.4 g.) and potassium cyanide (4.4 g.) was added ethyl acetate (20 ml.), and, to the mixture was added, under ice-cooling and stirring, the above neutralized solution of diazonium salt. The mixture was stirred for half an hour at room temperature and further stirred for half an hour at 70° C. The insolubles were removed by filtration, and the filtrate was extracted with ethyl acetate. The extract was washed with aqueous solution of sodium carbonate, diluted hydrochloric acid and water in the order mentioned, and dried. The solvent was evaporated off under reduced pressure, and the obtained residue was recrystallized from methanol to give colorless needles of 5-cyanospiro[benzo[b]furan-2(3H),1'-cyclopropane]-3-one (1.4 g.) m.p. 148°-149° C.
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