## 3 Results and Discussion
### Synthesis
It is clear that isomer **5** _anti_** was the major cycloadduct, because the steric effect of the nitrile group (CN). The bridge-head proton H-9 of the isomer _anti_**5** appeared at 8 5.46 ppm, which assigned, as triplet, with coupling constants J 2.4 Hz, on the other hand, the proton H-10 appeared at 4.60 ppm, as doublet, with coupling constants J 3.2 Hz, while the signal of the corresponding proton H-9\({}^{\prime}\) of the isomer _syn_**5** appeared at 8 4.44 ppm as triplet, with coupling constants J 2.8 Hz, and its signal assigned to the proton H-10\({}^{\prime}\) appeared at 8 5.71 ppm, as doublet, with coupling constants J 2.8 Hz. Moreover, the signals assigned to the proton H-9\({}^{\prime}\) of the decchlorinated isomer _dec_**5** appeared at upfield 8 4.39 ppm, as triplet, with coupling constants J 3.2 Hz, and its signal assigned to the proton H-10\({}^{\prime}\) appeared at 5 4.57 ppm, as doublet, with coupling constants J 2.4 Hz. The H-NMR signals of the unexpected dedhloration product **5** _dec_** are well-matched to the signal of this compound, as reported in literature [59]. The DA reaction of 1,8-dichloroanthracene **1** with 1-cyanovinyl acetate **3** afforded **6** _anti_, **6** _syn_, and **6** _dec_**. The steric effect of acetoxy substituent, beside the nitrile group on the dienophile, slightly increases the formation of regioisomer **6** _anti_**, since the ratio of **6** _anti_**: **6** _syn_**: **6** _dec_** regioisomers is 2.7:1:2.5, respectively. In case of 10-allyl-1,8-dichloroanthracene, only anti isomer had been obtained when allowed 10-allyl-1,8-dichloroanthracene to react with the same dienophile 1-cyanovinyl acetate **3**. This may be attributed to the strong steric effect of the ally substituent [25]. Interestingly, the tracing of these isomers on TLC using the solvent system EA/PE 1:5 showed that R\({}_{\text{f}}\) of **6** _anti_** is the largest one and R\({}_{\text{f}}\) of **6** _dec_** is larger than **6** _syn_ (Figure S3). After immersing this TLC in vanillin stain, the **6** _anti_** and **6** _syn_** exhibited yellow color, but **6** _dec_** did not. However, the **6** _dec_** spot was the most fluorescent \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Chemical Shift**} & \multicolumn{6}{c}{**Chemical Shift**} \\ \cline{2-13}
**Isomer** & \multicolumn{2}{c}{**H-9**} & \multicolumn{2}{c}{**H-9\({}^{\prime}\)**} & \multicolumn{2}{c}{**H-9\({}^{\prime\prime}\)**} & \multicolumn{2}{c}{**H-10**} & \multicolumn{2}{c}{**H-10\({}^{\prime}\)**} & \multicolumn{2}{c}{**H-10\({}^{\prime}\)**} \\ \cline{2-13}  & \(\delta\) & J & \(\delta\) & J & \(\delta\) & J & \(\delta\) & J & \(\delta\) & J & \(\delta\) & J \\ \hline
5 _anti_ & 5.46 & t; 2.4 & & & & & 4.60 & d; 3.2 & & & & \\
5 _syn_ & & & 4.44 & t; 2.8 & & & & & 5.71 & t; 2.8 & & \\
5 _dec_ & & & & & 4.39 & t; 3.2 & & & & & 4.57 & d; 2.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The distinguishing between the isomers **5** _anti_**, **5** _syn_, and **5** _dec_ using chemical shifts. under the UV lamp. Furthermore, the migration of these compounds on the TLC plate was consistent with their chemical nature, as the **6**_anti_ **and** **6**_syn_ **had two chlorine atoms, but the **6**_dec_ **did not. The NMR signals assigned to the bridge-head protons are presented in the Table 2. It is clear that isomer **6**_anti_ **is the major, because the steric effect resulted from the acetoxy (OCOCH**3**) and nitrile (CN) groups.