NEW SYMMETRICAL AND UNSYMMETRIC POLYFUNCTIONALIZED 2,2'-BIPYRIDINES

Recently, a large number of biheterocycles have been synthesized in or der to build macrobicyclic cryptates. To pursue investigations in this field, we prepared new symmetric and unsymmetric functionalized bipyr idines and we describe here two synthetic strategies leading to new te trasubstituted 3 to 15 and trisubstituted 17 to 29 bipyridines. Modifi cation at the alpha,alpha'-methyl groups and introduction of functiona lities in the 4,4'-positions have been performed after N-O activation of the starting 6,6'-dimethyl-2,2'-bipyridine unit. In the case of cya no and hydroxymethyl groups, alkylation of the N-O function followed b y a nucleophilic attack with the CN anion or an hydroxymethyl radical allowed us to obtain the dissymmetric species. To understand observed differencies between cyanation and hydroxymethylation processes, the u nstable and hygroscopic N-methoxybipyridinium salt 30 has been isolate d and characterized by nmr. Dibromomethyl compounds 8, 15, 29 were fin ally obtained in good to moderate yields by the Boekelheide rearrangem ent followed by a pseudohalogen exchange.