Synthesis of New Naphtho[2,3-f]quinoxaline-2,7,12(1H)-trione and Anthra-9,10-quinone Dyes from Furan-2,3-diones

Novel naphtho[2,3-f]quinoxaline-2,7,12(1H)-trione and anthra-9,10-quinone dyes were synthesized in good yield from furan-2,3-diones using 1,2-diaminoanthra-9,10-quinone and 1,4-diaminoanthra-9,10-quinone. The chromophores were characterized by molecular spectroscopy methods.


Introduction
Anthra-9,10-quinones and their condensed derivatives with heterocycles such as indanthrone (Pigment Blue 60, I), anthrapyrimidine (Pigment Yellow 108, II) and Vat Yellow 3 (III) (Figure 1) possess brilliant hues and very good fastness and represent an important group of vat dyes for the textile industry [1,2]. In addition to these properties, some anthra-9,10-quinone dyes are widely used in other fields, such as in medicine and food chemistry [3] and high-technology systems [4]. Consequently, anthra-9,10-quinones are interesting compounds from the viewpoint of both their reactions and applications.

Results and Discussion
Furan-2,3-dione starting materials 1a-f were prepared according to the literature [10][11][12][13]. The C 5 atom of compounds 1a-d smoothly reacted with the amino group of 1,2-DAAQ and 1,4-DAAQ to give compoubds 2 under mild conditions and in high yields (75-90%, Scheme 1). Due to the greater reactivity of the amino group attached to the C 2 atom of 1,2-DAAQ, compared with the amino group attached to the C 1 atom of 1,2-DAAQ, 1,2-DAAQ was modified from the amino group attached to C 2 -position of 1,2-DAAQ to give 2e. On the other hand, the amino group attached to the C 2 atom of 1,2-DAAQ did not react with the C 5 atom of 1a at higher temperature, but reacted with the C 3 atom of 1a by forming a Schiff base, which was not isolated (as outlined in Scheme 2). Through attack of the second amino group on the lactone carbonyl group, ring opening occurs. The reactions of 1,2-DAAQ with 1b,c,e,f run via the same reaction pathways to give 3 in nearly quantitative yields of 90-96% in boiling benzene. This proposed mechanism is similar to that reported in the literature for the reaction pathways of furan-2,3-diones with 1,2-diamino nucleophiles [9,14]. The structures of 2 and 3 were confirmed by spectroscopic data and agree with those found for similar compounds [4,9,14,15]. In the NMR spectra, the methine proton signal (low intensity) also revealed that compound 2 occurs as tautomers (2A and 2B), with tautomer 2B as a minor contributor in DMSO-d 6 solutions (Scheme 3). The 13 C-NMR spectroscopic data of 2 also agree with the proposed tautomeric structures.

AQ AQ
There was indication of tautomeric forms 3A (and 3B as a minor contributor) in 3a,f (but not 3b,c,e) in their 1 H-NMR spectra in DMSO-d 6 solution (Scheme 4). However, there was no signal for the methine proton belonging to the tautomer 3C in DMSO-d 6 solution. The 13 C-NMR spectra of 3 could not be recorded due to its very low solubility in organic solvents, but the condensation was verified by the detection of the [MH + ] and [MH + -H 2 O] signals.

General
Solvents were purchased from Merck and Carlo Erba. Diaminoanthra-9,10-quinones were purchased from Aldrich and used without further purification. 1 H-and 13 C-NMR spectra were recorded using a Bruker Ultrashield spectrometer operating at 300.

Conclusions
We have designed and easily synthesized novel naphtho[2,3-f]quinoxaline-2,7,12(1H)-triones and anthra-9,10-quinones in good to excellent yields as potential vat dyes from furan-2,3-diones. Their spectroscopic properties in solution and in the solid state are reported. For commercial dye production, reactions with high yields and relatively straightforward chemistry are preferred. It was seen that furan-2,3-diones have good reactivity to meet these expectations. We believe that preparation of various heterocyclic dyes based on furan-2,3-dione chemistry might make a contribution to the development of high performance pigments. Performances of new dyes will be tested in future studies.