C[C:2](C)([O-:4])C.[K+].[Br:7][C:8]1[CH:9]=[C:10]2[C:18](=[CH:19][CH:20]=1)[O:17][C:13]1([CH2:16][CH2:15][CH2:14]1)[CH2:12][C:11]2=[O:21].N1([CH2:31][OH:32])C2C=CC=CC=2N=N1>C1COCC1.CCOC(C)=O>[Br:7][C:8]1[CH:9]=[C:10]2[C:18](=[CH:19][CH:20]=1)[O:17][C:13]1([CH2:14][CH2:15][CH2:16]1)[C:12]([CH2:2][OH:4])([CH2:31][OH:32])[C:11]2=[O:21]A solution of potassium tert-butoxide (441 mg, 3.93 mmol) in THF (5 mL) was added to a suspension of 6-bromospiro[chromene-2,1′-cyclobutan]-4(3H)-one (500 mg, 1.87 mmol) and 1H-benzotriazole-1-methanol (586 mg, 3.93 mmol) in THF (5 mL) over 10 minutes in a dry ice-acetone bath under an argon atmosphere. The mixture was stirred for 0.5 hours in an ice bath, and then diluted with EtOAc (10 mL). After stirring for 0.5 hours, the mixture was filtered off. The filtrate was washed with 0.2 M aqueous NaOH (two times), water and brine, dried over MgSO4 and silicagel, filtered off. The filtrate was evaporated to give crude 6-bromo-3,3-bis(hydroxymethyl)spiro[chromene-2,1′-cyclobutan]-4(3H)-one (641 mg).
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