Unusual Product Distribution from Friedländer Reaction of Di- and Triacetylbenzenes with 3-Aminonaphthalene-2-carbaldehyde and Properties of New Benzo[g]quinoline-Derived Aza-aromatics

The Friedländer reactions of acetylbenzenes and 2-acetylpyridine with 3-aminonaphthalene-2-carbaldehyde afforded the corresponding 2-phenylbenzo[g]quinoline and 2-(pyrid-2-yl)benzo[g]quinoline, respectively. The same reactions of 3-aminonaphthalene-2-carbaldehyde with 1,2-, 1,3-, 1,4-di- and 1,3,5-triacetylbenzenes, however, afforded a series of corresponding (benzo[g]quinolin-2-yl)benzenes as new N,C-bidentate and unexpected benzo[g]quinoline. Crystallinity, thermal properties, absorption and emission spectral properties of the products were studied.

As a part of our interest in azapolyaromatics [25], we describe herein Friedländer reactions of acetylbenzene and polyacetylbenzenes with 3-aminonaphthalene-2-carbaldehyde for the synthesis of a series of benzo[g]quinoline-derived aza-aromatics and some properties of the resulting products.

Spectroscopic Properties
The ligands prepared could be readily characterized by 1 H-NMR spectral data and electrospray ionization mass spectrometry.Selected proton resonances are summarized in Table 1.Even though it was not always possible to completely resolve and assign all the proton resonances, certain features were characteristic and diagnostic enough to provide crucial clues about the structures.Typically, H 5 and H 10 of the benzo[g]quinoline (BQ) moiety and H 2 (and/or H 6 ) in the phenyl (Ph) ring of 3 are the ones to allow easy assignment by comparing their chemical shifts and splitting patterns as well as numbers of protons.In 3aa, H 5 and H 10 of BQ were resonated at δ 8.65 and 8.76 as an one-proton singlet, respectively, while H 2 and H 6 of Ph at δ 8.36 as a two-proton doublet of doublet (J = 8.1, 1.2 Hz).Introducing an additional BQ moiety on benzene ring usually resulted in downfield-shift of these protons.Introduction of BQ moiety to C 3 of the central benzene ring led to significant shift of H 2 of Ph by 0.76 ppm resonating at δ 9.12 as a one-proton triplet (J = 0.8 Hz).In tri-substituted system 3e, H 2 of Ph was resonated at δ 9.30 as a three-proton singlet due to the two adjacent N 1 's of BQ moiety that is comparable to those of 1,3,5-tri(azaheteroar-2-yl)benzenes [28,30].UV absorption spectra of 3 and 5, and the parent 4 in EtOH (1 × 10 −5 mol/L) were investigated, and the data are given in Figure 1 and Table 2.All compounds display intense absorption bands in the ultraviolet region 205-400 nm with extinction coefficients (ε) of ~10 5 , which are assigned to spin-allowed 1 LC transitions.The photoluminescence (PL) of the compounds was studied in EtOH (1 × 10 −5 mol/L) at room temperature and are given in Table 2. Excitation of the absorbance in the region 253-294 nm showed greenish blue light emissions in the range of 470-488 nm.The observed emission wavelength is somewhat dependent on the nature of the central benzene ring: Disubstituted ligands (3c, 3e, 5) showed emissions at 470 nm while monosubstituted ones (compounds 3aa, 3ab) showed them at 481 and 488 nm.The parent benzo[g]quinoline showed blue light emission at 435 nm.It should be noted that the emission of 3c and 3e were the relatively high compared to those (Figure 1).

Thermal and Structural Properties
The thermal behaviors of the compounds were analyzed by differential scanning calorimetry (DSC).All the compounds showed a single sharp endothermic peak at the melting transition temperature (T m ) and exothermic peaks at the crystallization temperature (T c ) as shown in Figure 2.However, none of the compounds showed glass transition temperature (T g ).It should be noted that compounds 3aa and 5 showed temperature increasing during crystallization implying that super cooling may be accompanied during crystallization.As a result, all the compounds prepared have good thermal stability despite of being relatively low molecular weight organic compounds.
The crystallinity of the compounds prepared was analyzed by XRD (X-ray diffraction) and X-ray diffractograms are shown in Figure 3.All of X-ray diffractograms of the compounds showed numerous distinctive peaks indicating their crystalline nature.

General Information
Melting points were determined using a Fischer-Jones melting points apparatus and are not corrected.UV spectra were recorded on a V550 spectrophotometer (Jasco, Tokyo, Japan).IR spectra were obtained using a 1330 spectrophotometer (Perkin-Elmer, city, state abbrev if US, country).NMR spectra were obtained using a Bruker-250 spectrometer (Fällanden, Switzerland) or VNS600 FT-NMR (Varian, Australia) for 1 H-NMR and 62.5 MHz for 13  was prepared employing a previously reported method [15].
C-NMR and are reported as parts per million (ppm) from the internal standard TMS.Chemicals and solvents were commercial reagent grade and used without further purification.Electrospray ionization (ESI) mass spectrometry (MS) experiments were performed on a LCQ advantage-trap mass spectrometer (Thermo Finnigan, San Jose, CA, USA).Elemental analyses were taken on a Hewlett-Packard Model 185B CHN analyzer (Hewlett Packard, Littleton, MA, USA).XRD analysis was performed by X-ray Diffractometer (Model: MPD for bulk, PANalytical, Wesybrough, MA, USA) with nickel-filtered CuKα radiation (30 kV, 30 mA) at 2θ angles from 10° to 90°, a scan speed of 10°/min and a time constant of 1 s.Thermal behaviors of the compounds were analyzed using differential scanning calorimetty (DSC Q200, TA Instrument, Wilminton, NJ, USA) with 1~2 mg of sample sealed in alumina in the range of 40-385 °C increasing temperature in a rate of 10 °C/min.An empty pan was used as a reference, and the DSC baseline, temperature, and enthalpy were calibrated.Starting 3-material aminonaphthalene-2-carbaldehyde(2)

Table 2 .
UV absorption and emission spectral data of 3, 4 and 5.