An unusual 1,2‐silyl shift during the reaction of an α‐oxo sulfine with an allylsilane

The reaction of 1-oxo-2-thioxo-indane S-oxide 1 with 1-(trimethylsilyl)-1 H-indene 2 gave endo-2-oxo-7-(trimethylsilyl)-5,6-benzo-2-thiabicyclo[2.2.1]hept-5-ene-3-spiro-2′-indan-1′-one 3 as the sole product. The crystal and molecular structure of the corresponding sulfone, 4, C21H22O3SSi, was established by X-ray diffraction analysis. The endo structure of the sulfoxide 3 was deduced from 1H NMR spectra. The formation of the product 3 can be explained by invoking a 1,2-silyl shift.