Photochemical and Thermal Reactions of a Kinetically Stabilized 9-Silaanthracene: The First Spectroscopic Observation of a 9,10-Dewar-9-silaanthracene Isomer

A kinetically stabilized 9-silaanthracene (1) underwent unique photochemical and thermal reactions to afford 9,10-Dewar-9-silaanthracene 2a and the head-to-tail [4 + 4] dimer 3, respectively. The structure of 2a was confirmed by 1H, 13C, and 29Si NMR spectra, and the kinetic parameters for the thermal reversion of 2a to 1 were obtained by the measurement of UV/vis spectra. The dimer 3 was thermally stable, and the molecular structure of 3 was determined by X-ray crystallographic analysis. It was experimentally demonstrated for the first time that 9-silaanthracene, as well as anthracene, can afford either the Dewar isomer or [4 + 4] dimer, depending on the reaction conditions.