Bridged ring systems isomerism

Cis-Trans Isomerism of Fused and Bridged Ring Systems... 

There are seven isomeric bicyclic rings of this class. Five have a bridge head nitrogen. Examples of all have been reported. A survey of this ring system has been included in a review [90AHC(48)223],... 

Bridging allenes such as 32 in the 4- and 5-positions by a butano fragment results in either the ds-cyclohexane derivative 347 or its trans-isomer. When the former is thermally isomerized the 10-membered ring system 348 is generated in practically quantitative yield, whereas trans-347 yields the diastereomer 349 [146],... 

The preference of 2,7-disubstituted oxepins for this tautomeric form at equilibrium may be rationalized in terms of a steric substituent effect. The eclipsing interactions of the 2,7-substituents in the arene oxide form will be diminished by isomerization to the oxepin. When the 2,7-substituents form part of an annelated ring system, e.g. (22)-(24), the tautomeric preference will be determined by the size of the methylene bridge (67AG(E)385). Thus when n = 5 the annelated oxepin (24) was present in approximately equal proportions with the arene oxide form. However with n =4. (23) tetralin 9,10-oxide was dominant. The... 

Triply bridging orf/io-phenylene complexes sometimes arise in curious ways. In the reaction of Os3(CO)10(MeCN)2 with salicylaldehyde benzy-limine one would naively expect that coordination would be through N and O atoms as with other metal systems. The first formed compound (40, Scheme 6) results from ortho metallation while, of the three isomeric decarbonylation products (41 to 43), compound 43 contains only Os—C bonds to the ligand and is a ring-substituted version of Os3H2(C6H4)(CO)9 (Scheme 6) (237). 

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