Bisdehydrothia annulenes

Bisdehydrothia-annulene (94) and the annulated bisdehydrooxa- and thia-annulenes (99 and 100) were synthesized73 in two steps as shown in Scheme 4, the key initial step entailing cross-condensation of 45 with properly designed dialdehydes. Acyclic models (93, 97, and 98) were reported to be quite unstable, and this appears to have prevented their... 

Starting from the aldehyde 192 and the bisphosphonium bromide, Br PhsP+CH -SCH2P Ph3Br , bisdehydrothia[17]annulenes 216, 217 and 218 and their oxidation products 219, 220, 221 and 222 have been prepared . A weak diatropicity was... 

The H-n.m.r. spectra of237 and 238 do not indicate any conformational mobility, in contrast to bisdehydrothia[13]- (227) and [17]annulenes (223 and 224) . It was found that the sulphides 237 and 238 are clearly paratropic 16tc electron systems. The H-n.m.r. spectrum of mono-cw-bisdehydrooxa[15]annulene (239) shows that it is atropic molecular models suggest that 239, unlike a -trans analogues (237 and 238), cannot be planar. 

---