Synthesis of amino- and bis(bromomethyl)-substitued bi- and tetradentate N-heteroaromatic ligands: Building blocks for pyrazino-functionalized fullerene dyads

Article abstract of DOI:10.1002/ejoc.200500548

In this paper we describe the synthesis of amino- and bis(bromomethyl)- substituted derivatives of phenanthrofine (phen), pyrazino[2,3-f]-phenanthroline (pphen), dipyrido[3,2-a:2′,3′-c]phenazine (dppz), pyrazino[2,3-i]dipyrido[3,2-a:2′,3′-c]phenazine, 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq) and 7,8-bis(2-pyridyl)pyrazino[2,3-g]quinoxaline. These substituted bi- and tetradentate N-heteroaromatic ligands are potential synthons for the preparation of the fullerene ligands 4-9. The diketones, 1,10-phenanthroline-5,6-dione 11a (phendione), 2,2-pyridyl 11b and 1,4-dibromo-2,3-butanedione 33 were used as starting materials. Phendione was converted into the phendiamine 13 by a two-step synthesis via the dioxime of the diketone 11a. Amino-substituted dppz and dpq derivatives were obtained by the reduction of the corresponding nitro compounds that were obtained by the Schiff base condensation of the diketones 11a and 11b and the appropriate o-phenylenediamine derivatives. An alternative synthetic route to the diamines 20a and 20b by detosylation of the diamino-substituted dppz and dpq ligands is also presented. Synthesis of the bis(bromomethyl)-substituted pphen, dpp, dppz and dpq derivatives was performed by the photochemical addition of bromine. Alternatively, synthesis of the bis(bromomethyl)-substituted pphen, pdppz and pdpq is also possible by the condensation of 1,4-dibromo-2,3-butanedione 33 and phendiamine or the diamino-substituted dppz and dpq derivatives. The latter two compounds can be also prepared by the condensation of diketones 11a and 11b with 6,7-diamino-2,3-bis(bromomethyl)-quinoxaline. Although the synthesis of some dppz and dpq ligands is already published, we herein present improved or alternative synthetic strategies leading to higher yields and/ or higher purity of these N-heteroaromatic ligands. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.