Naphthothiete und ihre Anwendung in der Heterocyclen‐Synthese

Naphtothietes and Their Application to the Synthesis of Heterocycles The three isomeric naphthothietes 5, 11 , and 16 were prepared according to the reaction sequences shown in Schemes 1–3. The final step was in each case a flash vacuum pyrolysis (FVP) of the corresponding mercaptonaphthalenemethanol 4, 9 , and 15 , respectively. The thiete rings in 5 and 11 can be opened by gentle heating; the ring opening of the isomer 16 possesses a much higher activation barrier. A MNDO calculation of the Δ H f values of 5, 11 , and 16 and the open isomers 5′, 11 ′, and 16 ′ provides an explanation for the different behavior. Photochemical ring opening represents a useful alternative. The reaction Schemes 4, 6, and 7 reveal the synthetic potential of the naphtho‐condensed thietes. Cycloaddition reactions with CC, CO, or CN double bonds lead into the series of differently condensed thiopyrans 17, 18, 24, 25, 26 , 3,1‐oxathiine 19 and 1,3‐thiazines 20, 21 .