Thermal and Ru-catalyzed Reactions of Styryl-Substituted Azulenes with Dimethyl Acetylenedicarboxylate
-
Source and publish data:
Helvetica Chimica Acta p. 1940 - 1968 (1994)
Update date:2022-08-05
Topics:
-
Authors:
Briquet, Anne Andree Sophie
Hansen, Hans-Juergen
Article abstract of DOI:10.1002/hlca.19940770723
The thermal reaction of 1-<(E)-styryl>azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin at 190-200 deg does not lead to the formation of the corresponding heptalene 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 -catalized reaction of 4,6,8-trimethyl-1-<(E)-4-R-styryl>azulenes (R=H, MeO, Cl; Scheme 4) with ADM in MeCN at 110 deg 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 (3-5percent; Scheme 4).The benzanellated azulenes trans-10a and trans-10b are also found in small amounts (2-3percent) 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 (1-3percent).Similar results are obtained in the -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 (29percent).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 (10percent).Again, the main product is the corresponding azulene-1,2-dicarboxylate 25 (20percent).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 (28percent) as well as Ru-catalyzed in MeCN (40percent).Whereas only small amounts of the azulene-1,2-dicarboxylate 8 (1 and 5percent, respectively) are formed, the corresponding benzanellated azulene trans-29 is found to be the second main product 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 deg in decalin and at 110 deg in MeCN by catalysis.The yields (30percent) are much better in the catalized reaction.The formation of by-products (e.g. 39-41; Scheme 14) in small amounts (0.5-5percent) in the Ru-catalized 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).
View More
Full text of DOI:10.1002/hlca.19940770723