6′-Bromospiro[cyclobutane-1,2′-inden]-1′(3′H)-one (Intermediate 38, 1.1 g, 4.38 mmol), 2-methylpropane-2-sulfinamide (0.96 g, 7.88 mmol), and titanium ethoxide (1.805 mL, 8.76 mmol) were dissolved in methyl THF (20 mL), and heated to reflux overnight. The reaction was allowed to cool to r.t., then it was diluted with EtOAc (150 mL). Water (22 mL) was added dropwise over 10 min under vigorous stirring and then the mixture was left standing without stirring for 1.5 h. The solids were filtered off and the organics were evaporated to give a crude product which was purified by flash chromatography (eluent: heptane/ethylacetate 8:1) to afford the title compound (2.1 g, 77% yield), used as such in the next step: MS (ES+) m/z 354 [M+H]+.
