Keitaro Nishino

A REMARKABLY STABLE AND SIMPLE MONOCYCLIC THIEPIN. SYNTHESIS AND PROPERTIES OF 2,7-DI-TERT-BUTYL-4-ETHOXYCARBONYL-5-METHYLTHIEPIN

A simple monocyclic 8n electron thiepin, 2,7-di-tert-butyl-4-ethoxycarbonyl-5-methylthiepin (13) stabilized by two bulky tert-butyl groups at 2and 7-positions, was synthesized from 2,6-di-tert-butyl-4-methylthiopyrylium tetrafluoroborate (11). In spite of of its monocyclic thiepin structure, the compound 13 showed remarkable thermal stability and had a half-life of 7.1 h at 130 °C. Judging from the 1H-NMR spectrum, the thiepin 13 is considered to be an atropic molecule. Synthetic details of 11 and 13, and the chemical and physical properties of 13 are also described.