Quinoxaline-2,3-diones table

Attempts to directly iodinate quinoxaline failed, and the synthesis of 2,3-diphenyl-5,8-dibromoquinoxaline is somewhat more involved (Scheme 9) [61]. Starting from ort/zo-phenylenediamine, reaction with SOCI2 gives benzothia-diazole in high yield. Bromination in HBr furnishes 4,7-dibromobenzothiadi-azole, which can be alkynylated or directly reduced [62]. Reduction of the dibromide with sodium borohydride leaves the halide substituents unmolested but opens the ring to furnish l,4-dibromo-2,3-diaminobenzene. Reaction of this intermediate with a 1,2-dione furnishes a 2,3-disubstituted 5,8-dibromo-quinoxaline. Pd-catalyzed alkynylation finishes the sequence off and removal of the TMS groups yields the desired 5,8-diethynylquinoxaline monomers (Table 9, entries 13,14). 

Further mechanochemical 1,2-dione/diamine condensation reactions were described by Kaupp and Naimi-Jamal in their subsequent article [4]. Substituted quinoxalines 9 were obtained by ball milling of equimolar amounts of o-phenylenediamines 7 and benzyls 8 (Scheme 3.3, Table 3.1). Milling beaker was heated at different temperatures through double walls with fittings for circulating... 

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