Thermal Reaction of Azulene and Some of Its Symmetrically Substituted Methyl Derivatives with Dimethyl Acetylenedicarboxylate

Abstract

It is shown that azulene (1) and dimethyl acetylenedicarboxylate (ADM) in a fourfold molar excess react at 200° in decalin to yield, beside the known heptalene-(5) and azulene-l,2-dicarboxylates (6), in an amount of 1.6% tetramethyl ( 1RS,2RS,5SR,8RS)-tetracyclo[6.2.2.22~5O'~5~tetradeca-3,6,9,l 1,13-pentaene-3,4,9,lO-tetracarboxylate ('anti'-7) as a result of a SHOMO(azulene)/LUMO(ADM)-controlled addition of ADM to the seven-membered ring of 1 followed by a Diels-Alder reaction of the so formed tricyclic intermediate 16 (cf: Scheme 3 ) with a second molecule of ADM. The structure of 'anti'-7 was confirmed by an X-ray diffraction analysis. Similarly, the thermal reaction of 5,7-dimethylazulene (3) with excess ADM in decalin at 120° ied to the formation of eu. 1 % of 'anti'-12, the 7,12-dimethyl derivative of 'anti'-7, beside of the corresponding heptalene-10 and azulene-l,2-dicarboxylates 11 (cf. Scheme 2 ) . The introduction of Me groups at C(l) and C(3) of azulene (1) and its 5,7-dimethyl derivative 3 strongly enhance the themial formation of the corresponding tetracyclic compound. Thus, 1,3-dimethylazulene (2) in the presence of a sevenfold molar excess of ADM at 200" yielded 20% of 'anli'-9 beside an equal amount of dimethyl 3-methylazulene-l,2-dicarboxylate (8; cf. Scheme I ) , and 1,3,5,7-tetramethylazulene (4) with a fourfold molar excess of ADM at 200' gave a yield of 37% of 'unti'-15 beside small amounts of the corresponding heptalene-13 and azuIene-1,2-dicarboxylates 14 (cf. Scheme 2 ) .

Excursion to the World of Heptacyclic Compounds Made of Azulenes and Acetylenedicarboxylates

“…There are indeed two thermal pathways for the reaction between azulenes and ADM leading to the primary intermediates of type A and B [5]. In the presence of an excess of ADM both intermediates can be trapped by a Diels-Alder reaction of their conjugated diene system with ADM, thus resulting in stable tetracyclic tetracarboxylates (see, e.g., [6]). Moreover, the type B intermediates undergo a reversible thermal sigmatropic [1,5]-C shift to form B' structures [7] [8].…”

A Detailed Investigation of the Reaction of 5,9-Diphenylbenz[a]azulene with Dialkyl Acetylenedicarboxylates Leading to Dialkyl 8,12-Diphenylbenzo[a]heptalene-6,7-dicarboxylates

“…[5] [18] [19]). Compounds of type 12 were present in small amounts in all reaction mixtures of 3a ± 3d and ADR.…”

“…Similarly, tricyclic compounds of type 12a are often formed in the thermal reactions of azulenes with ADM. They represent Diels-Alder adducts of ADM with the seven-membered ring of azulenes, resulting from a SHOMO(azulene) controlled reaction [5] [18] [19].…”

Synthesis of Polyalkylphenyl Prop-2-ynoates and Their Flash Vacuum Pyrolysis to Polyalkylcyclohepta[b]furan-2(2H)-ones

“…This variant is perfectly well-suited for the synthesis of azulenes without substituents at C(4) and C(8) (cf. also [19]), which are not available by the original pyrylium salt route (cf. [20]).…”

“…Formation of 1,2,3,4-Tetrahydrobenz[a]azulenes. ± We reacted the furanones 3c, 3e, and 3f with 1-(cyclohex-1-enyl)pyrrolidine (19) in toluene in order to test the azulene-forming propensity of these highly methylated cyclohepta[b]furan-2(2H)-ones (Scheme 15) 15 ). Indeed, in all three cases the generation of the blue azulene color was recognized.…”