Carbonyl and thiocarbonyl stabilized 1,4-dihydropyrazines: synthesis and characterization
Three analogues of the 1,4-dihydropyrazine, 3,4,7,8-tetrahydro-4,4,8,8-tetramethyl-2,6-dioxa-4a,8a-diazaanthracene-1,5-dione (DDTTA), have been synthesized. 2,4,4,6,8,8-Hexamethyl-3,4,7,8-tetrahydro-2,4a,6,8a-tetraazaanthracene-1(2H),5(6H)-dione (HTTA) is synthesized by chlorination of the previously reported 5,6-dihydro-1,3,5,5-tetramethylpyrazin-2(1H)-one with tert-butyl hypochlorite and self condensation of the resulting α-chloromethylimine in the presence of diisopropylethylamine in dimethylformamide (DMF). Thioxo derivatives 3,4,7,8-tetrahydro-4,4,8,8-tetramethyl-5-thioxo-2,6-dioxa-4a,8a-diazaanthracen-1-one (DDTTA–S) and 3,4,7,8-tetrahydro-4,4,8,8-tetramethyl-2,6-dioxa-4a,8a-diazaanthracene-1,5-dithione (DDTTA–S2) have been synthesized by direct thionation of DDTTA with phosphorus pentasulfide in pyridine. All three molecules have been characterized spectroscopically. In addition the crystal structure of HTTA has been determined. Radical cations obtained by one electron oxidation of the dihydropyrazines have been characterized by electron spin resonance spectroscopy.