## 3 Results and Discussion  
### Synthesis  
The starting material 1,8-dichloroanthracene **1** was prepared in a good yield from commercially available 1,8-dichlorroauthracquinone, according to the [PERSON] et al. procedure [47]. A literature survey revealed that 1,8-dichloroanthracene **1** is not reactive in DA reaction as anthracene itself. For example, [PERSON] et al. [48] reported the DA reaction between 1,8-dichloroanthracene **1** and phenyl vinyl sulfoxide; the reaction was under N\({}_{2}\) at chlorobenzene reflux (130 \({}^{\circ}\)C) and gave the cycloadduct in 30% yield after an 8-day reaction time, while [PERSON] et al. reported the successful DA reaction in 83% yield between the same dienophile and anthracene [34]. With the line of our interest on the DA reaction, 1,8-dichloroanthracene **1** reacted with acrylonitrile, 1-cyanovinyl acetate, and phenyl vinyl sulfone to investigate the substituents effect in terms of regioselectivity. Initially, the reaction of phenyl vinyl sulfone--with 1,8-dichloroanthracene **1**, either in dichloromethane or toluene, under reflux conditions for 10 h--did not occur. Obviously, the reaction of 1,8-dichloroanthracene **1** with dienophiles is a challenge, and to get successful may be the reaction should be run under harsher conditions. An alternative way is to use the microwave-assisted organic synthesis technique because it has advantages compared to the conventional method, including being faster, safer, greener, more selective, and more economic [49; 50; 51]. This technique became an efficient tool in all organic reactions, including DA reaction [52; 53]. We successfully synthesized the ethanoanthracenes via DA reaction with the microwave-assisted synthesis approach (Scheme 1). The DA reactions of anthracenes with dienophiles, which lead to the possible formation of more than products, in terms of regioselectivity and stereoselectivity, have attracted the attention of more researchers. The effects of the substituent nature on the reaction of 2-substituted anthracenes with malic anhydride, affording two isomeric adducts, have been reported [54]. The substituent on the 1-position of anthracenes exerted a significant steric effect on the reaction stereoselectivity [55]. The steric factor of the substituent on the 1-position of 1-succinimidoanthracene and 1-phthalimidoanthracene was found to favor anti adduct formation [56]. On the other hand, when the substituent located in the 2-position postulated to have no steric effect as well, no major electronic effect could be explained in terms of the mechanism of the reaction [54]. However, the determination ratio of the two possible adducts was initiated as an approach to investigate the reaction mechanism [57]. [PERSON] et al. reported that the amino group has an electronic effect on the isomer ratio when it is located in the 1- or 2-position of anthracene moiety [58]. In our previous work, the steric effect was found to play a major role on the regioselectivity of the DA reaction of 10-allyl-1,8-dichloroanthracene with 2-chloroacrylonitrile, 1-cyanovinyl acetate, and phenyl vinyl sulfone [25]. Recently, we reported the DA reaction of 1,8-dichloroanthracene **2** and 2-chloroacrylonitrile under xylene reflux for 48 h affording two regioisomers in a 2:1 ratio [43]. The synthetic route towards target regioisomers (**5-7**) _anti_, (**5-7**) _syn_, and (**5-7**) _dec_ is shown in Scheme 1. As a result of the reaction, 1,8-dichloroanthracene **1** with acrylonitrile **2**, regioisomers **5** _anti_, **5** _syn_, and **5** _dec_ were obtained as a mixture in a ratio 3.02:1.41:1, respectively (Supplementary Materials Figures S1 and S2). It sounds that the steric effect of the nitrile group, to chlorine atom, plays a crucial role in favor of regioisomer **5** _anti_. The NMR signals assigned to the bridge-head protons are usually utilized for isomer identification, and regiooselectivity [5; 16; 18; 19; 25], (Table 1, Figure S2).