A Potential Iterative Approach to 1,4‐Dihydro‐N‐Heteroacene Arrays

Abstract

A new method for the synthesis of substituted 1,4‐dihydrophenazines is reported and the structure of N‐butyl‐5‐methyl‐3‐nitro‐5,10‐dihydrophenazine is proven by an X‐ray single‐crystal structure determination.

Potential Building Blocks for 1,4‐Dihydro‐N‐heteroacenes

“…After preparing small batches of 2‐(butylamino)‐5‐methyl‐3‐nitro‐5,10‐dihydrophenazine 4 [39] a number of times we noticed a more polar red product on the flash silica column (Figure 2 ). This was only observed when old batches of the starting material, kept in the dark in a sealed sample vial for about eight weeks, were used.…”

“…We recently reported groundwork for a potential iterative approach to prepare N ‐heteroacenes (Scheme 1 ). [39] 1,2‐Difluoro‐4,5‐dinitrobenzene 2 has dual‐mode or ambident reactivity. The fluorine atoms are firstly displaced by diamine 1 , forming N ‐methylphenazine 3 and a nitro group is displaced [40] next by butylamine forming compound 4 .…”

“…Samples were purified by chromatography on flash silica with gradient elution. Some starting material was eluted followed by compound 7 then compound 8 , [39] which was characterised by diffraction measurements (Figure 3 ). Compound 7 was fully characterised and its structure was inferred from the structure of the butylamine displacement product 6 .…”

“…The products were purified by chromatography on silica gel. CH 2 Cl 2 eluted the starting material (7 mg, 14 %), Et 2 O, then MeOH/Et 2 O (1 : 99) eluted 2‐(butylamino)‐5‐methyl‐3‐nitro‐5,10‐dihydrophenazine 4 [39] (8 mg, 15 %) and MeOH/Et 2 O (10 : 90) eluted the title compound 6 (5 mg, 8 %), mp: >200 °C (from dichloromethane:light petroleum ether).…”

“…A batch of 5‐methyl‐2,3‐dinitro‐5,10‐dihydrophenazine 3 that was over 8 weeks old and had been stored in a sealed vial (15 mg, 0.052 mmol) was purified by chromatography on silica gel. CH 2 Cl 2 eluted the starting material (10 mg, 67 %), then CH 2 Cl 2 /MeOH (10 : 90) eluted the title compound 7 (1 mg, 6 %), then 10‐methyl‐3‐nitrophenazin‐2‐(10 H )‐one [39] 8 (4 mg, 30 %), mp: >200 °C (from dichloromethane:light petroleum ether).…”