Water → 2-Bromo-5,6-dichloro-indan-1-ol

According to Scheme 2, step IV: To a solution of 5,6-dichloro-1H-indene (5f) (1.28 g, 6.92 mmol), which was obtained according to Scheme 2 by following a reaction sequence according to synthesis of (5a), in dimethylsulfoxide (6.5 ml) and water (0.16 ml) N-bromosuccinimide (2.44 g, 13.7 mmol) was added at 10° C. and the mixture was stirred at 25° C. for 1 h. The mixture was poured on water, stirred for 30 min and the solid material was filtered off. The crude product was purified by silica gel chromatography (eluting with 0 to 50% ethyl acetate in heptane) to give 1.46 g of 2-bromo-5,6-dichloro-indan-1-ol which was immediately dissolved in tetrahydrofuran (35 ml). Finely powdered NaOH (1.37 g, 34.2 mmol) was added and the mixture was stirred at 25° C. for 2 h. The mixture was filtered through a short pad of celite and washed with a small amount of ethyl acetate. The filtrate was evaporated to dryness to give 1 g of racemic(1aS,6aR)-3,4-Dichloro-6,6a-dihydro-1aH-1-oxa-cyclopropa[a]indene (6f), which was used in the next step without purification.