Hexatrienes annulated

Thiemann and coworkers [68] sought novel types of steroids with different biological activity, and in doing so prepared areno-annulated compounds such as 6/1-133 (Scheme 6/1.35). This is achieved with a Heck reaction of 6/1-132 with an acrylate, followed by an electrocydic ring closure of the formed hexatriene. The reaction is then terminated by removal of the nitro group, with formation of the aromatic ring system. 

The heavily annulated benzo- and furanothia[ll]annulenes depicted in 6182 and 6283 were synthesized by condensation of dialdehyde (47) with properly structured Wittig components. Further, treatment of 62 with maleic anhydride produced a mixture of endo and exo cycloadducts of general formula 63 whose hexatriene segment that was not directly bound to the heteroatom was found to be thermally labile, readily... 

Mono-annulated 1,3,5-hexatrienes leading to ort/io-condensed 1,3-cyclohexadienes of the types I-IV (see Figure 2) have been well studied. By contrast, bridged trienes leading to 1,3-cyclohex ienes of types V-IX are rare. This section is organized sequentially according to the 1,3-cyclohexadiene type. 

Thiemann et al. [92] prepared steroid analogues containing an areno-annulation as in 169 (Scheme 8.44). They also used a combination of a Mizoroki-Heck reaction and an electrocyclic ring closure of an intermediately formed 1,3,5-hexatriene. Thus, reaction of... 

Hexatriene intermediates 2.175e,f were isolated from the reaction involving acyclic alkenes (Scheme 2.61). It was suggested that another reaction route occurred in the case of tricyclic ruthenacycles III because their conformation promotes p-elimination with reductive elimination leading to tricyclic cyclohexadienes 2.177. Steric constraints being produced by the annulated ring [112]. 

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