Sondheimer annulene synthesis

Scheme 3. Intramolecular acetylenic coupling in annulene synthesis described by Sondheimer[8] according to the method of Eglinton and Galbraith [7],...

The preparation of l,6-oxido[10]annulene, described simultaneously by Sondheimer and Shani4 0 and by Vogel, Biskup, Pretzer, and Boll, is illustrative of the rather general synthesis of aromatic 1,6-bridged [10]annulenes starting from 1,4,5,8-tetrahydronaphthalene. Apart from the present compound, the following bridged [10]annulenes have thus far been obtained by this approach l,6-methano[10J-annulene,2-8-9 the ll,ll-dihalo-l,6-methano[10]annulenes,9 10 and 1,6-imino [ 1 OJannulene.11... 

Only two general methods have been developed for the synthesis of the macrocyclic annulenes.9 The first of these, developed by Sondheimer and co-workers, involves the oxidative coupling of a suitable terminal diacetylene to a macrocyclic polyacetylene of required ring size, using typically cupric acetate in pyridine. The cyclic compound is then transformed to a dehydroannulene, usually by prototropic rearrangement effected by potassium i-butoxide. Finally, partial catalytic hydrogenation of the triple bonds to double bonds leads to the annulene. 

The method of synthesis is essentially that described by Sondheimer and Wolovsky3 (preparation of tridehydro[18]annulene) and by Sondheimer, Wolovsky, and Amiel2 (hydrogenation of tridehydro[18]-annulene to [18]annulene). It has been simplified, since [18]annulene is... 

Sondheimer, F., Wolovsky, R. Amiel, Y. 1962 Unsaturated macrocyclic compounds. XXIII. The synthesis of the fully conjugated macrocyclic polyenes cyclooctadecanonaene ([18]annulene), cyclotetracosadodecaene (r241annulene) and cyclotriacontapentadecaene (f301annulene). J. Am. chem. Soc. 84, 274-284. 

Considering this situation Becby and Sondheimer have carried out the first synthesis of a bisdehydroaza[17]annulene having a methylene bridging chain . ... 

Thus, Sondheimer s famous synthesis of [18]annulene (145) employs the hydrogenation of an acetylenic precursor in the last step (Scheme 8-19). Recently, hydrogenation of cyclic diene-diynes has been used for the preparation of interesting cyclic tetraenes, such as tetrahomocy-clooctatetraene 146 [Eq. (23)] [Sa]. 

---