The thermal reaction of 1[(E)-styryl]azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin at 190-200 degrees does not lead to the formation of the corresponding heptalene-1,2-dicarboxylates (Scheme 2). Main products are the corresponding azulene-1,2-dicarboxylates (see 4 and 9), accompanied by the benzanellated azulenes trans-10a and trans-11, respectively. The latter compounds are formed by a Diels-Alder reaction of the starting azulenes and ADM, followed by an ene reaction with ADM (cf. Scheme 3). The [RuH2(PPh(3))(4)]-catalyzed reaction of 4,6,8-trimethyl-1-[(E)-4-R-styryl]azulenes (R=H, MeO, Cl; Scheme 4) with ADM in MeCN at 110 degrees yields again the azulene-1,2-dicarboxylates as main products. However, in this case, the corresponding heptalene 1,2-dicarboxylates are also formed in small amounts (3-5%; Scheme 4). The benzanellated azulenes trans-10a and trans-10b are also found in small amounts (2-3%) in the reaction mixture. ADM Addition products at C(3) of the azulene ring as well as at C(2) of the styryl moiety are also observed in minor amounts (1-3%). Similar results are obtained in the [RuH2(PPh(3))(4)]-catalyzed reaction of 3-[(E)-styryl]guaiazulene ((E)-8; Scheme 5) with ADM in MeCN. However, in this case, no heptalene formation is observed, and the amount of the ADM-addition products at C(2) of the styryl group is remarkably increased (29%). That the substituent pattern at the seven-membered ring of(E)-8 is not responsible for the failure of heptalene formation is demonstrated by the Ru-catalyzed reaction of 7-isopropyl-4-methyl-1-[(E)-styryl]azulene ((E)-23; Scheme 11) with ADM in MeCN, yielding the corresponding heptalene-1,2-dicarboxylate (E)-26 (10%). Again, the main product is the corresponding azulene-1,2-dicarboxylate 25 (20%). Reaction of 4,6,8-trimethyl-2-[(E)-styryl]azulene ((E)-27; Scheme 12) and ADM yields the heptalene-dicarboxylates (E)-30A/B, purely thermally in decalin (28%) as well as Ru-catalyzed in MeCN (40%). Whereas only small amounts of the azulene-1,2-dicarboxylate 8 (1 and 5%, respectively) are formed, the corresponding benzanellated azulene trans-29ist found to be the second main product (21 and 10%, respectively) under both reaction conditions. The thermal reaction yields also the benzanellated azulene 28 which is not found in the catalyzed variant of the reaction. Heptalene-1,2-dicarboxylates are also formed from 4-[(E)-styryl]azulenes (e.g (E)-33 and (E)-34; Scheme 14) and ADM at 180-190 degrees in decalin and at 110 degrees in MeCN by [RuH2(PPh(3))(4)] catalysis. The yields (30%) are much better in the catalyzed reaction. The formation of by-products (e.g. 39-41; Scheme 14) in small amounts (0.5-5%) in the Ru-catalyzed reactions allows to understand better the reactivity of zwitterions (e.g. 42) and their tricyclic follow-up products (e.g. 43) built from azulenes and ADM (cf. Scheme 15).
