Formation of Unusual Products from the Acid-Catalyzed Reaction of Azulenes with Dimethyl Acetylenedicarboxylate

Brügger, Paul; Uebelhart, Peter; Kunz, Roland W.; Sigrist, Rolf; Hansen, Hans‐Jürǵen

doi:10.1002/(sici)1522-2675(19981216)81:12<2201::aid-hlca2201>3.0.co;2-7

Cited by 5 publications

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“…In this respect, the formation of 11 is a good indicator that the intermediates 12 are indeed formed (cf., e.g., [2] [4]). The azulen-1-yl-substituted maleates (Z)-10 and the diastereoisomeric fumarates (E)-10 are generally formed from the corresponding azulenes and ADM in protic solvents (cf., e.g., [5] [11]), but may also be generated in small amounts in other solvents. In the present case, it is of interest to note that we could detect only the (Z)-isomers.…”

supporting

confidence: 68%

“…Both, the (Z)-and (E)-isomers can easily be differentiated by their 1 H-NMR spectra, since HÀC(2) as well as MeOCOÀC (2) show for the (Z)-and (E)-forms great and inverse shift differences (cf. [5] [11] and Exper.…”

mentioning

confidence: 82%

“…85 (2002) 29 unsymmetrical substitutions patterns of azulenes such as those in benz[a]azulenes may change this situation and give rise to the formation of 14 as intermediates [6] [13]. However, two-step reactions of azulenes and ADM via free zwitterions of type 15 [5], or as given by Lewis-acid catalysis, always result in the cis-configured intermediates 14 [11], which possess, similarly as the tricycles 13, large DDH f 8 values with respects to the reactants. All of the primary intermediates 12 ± 14 are prone to undergo further addition reactions with ADM.…”

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confidence: 99%

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New Products from the Heptalene-Forming Reaction of Azulenes and Acetylenedicarboxylates in Polar Media

Singh¹,

Linden²,

Abou‐Hadeed³

et al. 2002

HCA

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A number of azulenes 1, in particular those with p-substituents at C(6) such as phenyl, 3,5-dimethylphenyl, and 4-biphenyl, have been reacted with 3 mol-equiv. of dimethyl acetylenedicarboxylate (ADM) in MeCN at 1108 (cf. Scheme 1). Main products had been, in all cases, the corresponding heptalene-4,5-dicarboxylates 2. However, a whole number of side products, mainly rearranged (1 2)-adducts with two molecules of ADM, in amounts of 0.2 ± 9% were also isolated and characterized (cf. Scheme 2). The 2a,8a-dihydro-3,4-ethenoazulene-1,2-dicarboxylates 14, formed by energetically favorable ring closure from the solvent-stabilized zwitterions 15, resulting from bond heterolysis in the primary cycloadducts 12 (cf. Scheme 3), have been mechanistically identified as the pivotal intermediates responsible for the formation of all side product (cf. Schemes 5, 9, 12, and 13). Deuterium-labeling experiments were in agreement with the proposed mechanisms, indicating that sigmatropic [1,5s]-H shifts in 14 (cf. Scheme 6) as well as isoconjugate [1,4s]-H shifts in resonance-stabilized zwitterions of type 21 (cf. Scheme 9) are the crucial steps for side-product formation. It is postulated that a concluding antarafacial 8e-dyotropic rearrangement is responsible for the appearance of the 2,4a-dihydrophenanthrene-tetracarboxylates of type trans-6 (cf. Scheme 9) in the reaction mixtures, which further rearrange thermally by a not fully understood mechanism into the isomeric tetracarboxylates 7 (cf. Schemes 10 and 11). Most surprising is the presence of a small amount (0.3 ± 1%) of the azulene-4,5,7,8-tetracarboxylate 9 in the reaction mixture of azulene 1a and ADM. It is proposed that the formation of 9 is the result of a [1,5s]-C shift in the spiro-linked intermediates 24, which, after prototropic shift and take-up of a third molecule of ADM, disintegrate by a retro-Diels-Alder reaction into 9 and the phthalic diesters 30 (cf. Scheme 12). The UV/VIS spectra of the p-substituted heptalene-4,5-dicarboxylates 2d ± 2f and their double-bond shifted (DBS) forms 2d ± 2f (cf. Table 4 and Figs. 9 ± 12) exhibit in comparison with the heptalene-dicarboxylates 2a and 2'a, carrying a t-Bu group at C(8), only marginal differences, which are mainly found in the relative intensity and position of heptalene bands II and III.

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confidence: 82%

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New Products from the Heptalene-Forming Reaction of Azulenes and Acetylenedicarboxylates in Polar Media

Singh¹,

Linden²,

Abou‐Hadeed³

et al. 2002

HCA

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“…ADM and a catalytic amount of trifluoroacetic acid (TFA; ca. 5 mol-% with respect to applied ADM) [12]. The most important products, which we found beside recovered 1a (75%) by chromatographic workup, are displayed in Scheme 2.…”

Section: Reaction Of Azulenes With Acetylenedicarboxylates Under Acidmentioning

confidence: 94%

“…In another context, we already published the results of the crystal-structure determination of 6b [13] [12]). The X-ray crystal structure of dimer 8b revealed the presence of two independent molecules in the asymmetric unit, which differed only slightly in the relative spatial orientation of the ester groups at C(1)=C (2) and C(1')=C(2').…”

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confidence: 99%

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

Chen

Lehto

Uebelhart

et al. 2015

Helvetica Chimica Acta

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Azulenes and acetylenedicarboxylates react under acid catalysis (Brønsted or Lewis) and form (2aRS,8aSR)-2a,8a-dihydrocyclopenta[cd]azulene-1,2-dicarboxylates as intermediate products, which then dimerize by central bond-formation between C(2a1) and C(2'a1) and various peripheral C,C'-atoms of the dihydroazulene fragments, depending on the substituents present. The reactions are often accompanied by the formation of side-products, such as 2-(azulen-1-yl)fumarates and -maleates and others caused by H-shifts of the primary intermediates. H-Shifts between the two tetrahydrocyclopenta[ cd]azulene parts of the heptacyclic structures were also found.

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New Results in Homoheptalene Chemistry

Rüedi

Hansen

2001

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The thermal reaction of homoazulene ( bicyclo[5.3.1]undeca-1,3,5,7,9-pentaene; 2) with dimethyl acetylenedicarboxylate (ADM) in 1,2-dichloroethane (ClCH 2 CH 2 Cl) results, in contrast to an earlier report [5], in formation of not only dimethyl homoheptalene-4,5-dicarboxylate ( bicyclo[5.5.1]trideca-1,3,5,7,9,11-hexaene-4,5-dicarboxylate; 3), but also of a 4 : 1 mixture of 3 and dimethyl homoheptalene-2,3-dicarboxylate (13) in almost quantitative yield (Schemes 1 and 3). The structures of both homoheptalenes have been corroborated by X-ray crystal-structure analysis (Fig. 5). The double-bond-shifted (DBS) isomers 3' and 13' of 3 and 13, respectively, could not be detected in their 1 H-NMR spectra (600 MHz threshold of detection ! 0.5%), in agreement with the AM1-calculated DH o f values of the four isomeric homoheptalene-dicarboxylates (cf . Table 4). Vilsmeyer formylation of homoazulene (2) gave homoazulene-8-carbaldehyde (14) in a yield of 67%, which, on treatment with benzylidene-(triphenyl)-l 5 -phosphane, gave, in almost quantitative yield, a 1.6 : 1 mixture of (Z)-and (E)-8-styrylhomoazulene ((Z)-15 and (E)-15, resp.). Thermal reaction of the latter mixture with ADM in 1,2-dichloroethane led, in a yield of 42%, to a 5 : 1 mixture of dimethyl (Z)-and (E)-2-styrylhomoheptalene-4,5-dicarboxylate ((Z)-15 and (E)-16, resp.). Both isomers were separated by column chromatography on silica gel. Again, the DBS isomers of (Z)-16 and (E)-16, i.e., (Z)-16' and (E)-16', could not be detected in the 1 H-NMR spectra (600 MHz) of pure (Z)-16 and (E)-16.1. Introduction. ± The class of homoheptalenes ( bicyclo[5.5.1]trideca-1,3,5,7,9,11-hexaenes) is still sparsely populated, although the parent structure was synthesized more than 25 years ago by Vogel et al.[1]. Line-shape analysis of the 13 C-NMR signals of homoheptalene (1a) in the temperature range of 153 ± 233 K gave an activation energy (E a ) of 5 kcal´mol À1 for the double-bond-shift (DBS) process in this [12]annulene, which is slightly higher than that for heptalene itself (3.5 kcal´mol À1 ), which was derived by the same procedure [2]. Two X-ray crystal-structure analyses of the homoheptalene derivatives 1b [3] and 1c [4] have been performed (see below) that show the p-core to be composed of two cycloocta-2,4,6-triene substructures with the homo-C(sp 3 )-atom and its two attached C(sp 2 )-atoms in common and with a c 2 axis passing through the bridging C-atom (see the AM1-calculated structure of 1a in Fig. 1, which is in good agreement with the X-ray crystal structures of 1b and 1c (Sect. 2.2). Later, Scott and Kirms applied Hafners synthesis of dimethyl heptalene-4,5-dicarboxylates by thermal reaction of azulenes and dimethyl acetylene-dicarboxylate (ADM) (cf.[5]) to homoazulene (2), for which Scott et al. had developed a new and efficient synthesis [6]. They reported that 2 reacts smoothly with ADM in boiling 1,2-dichloroethane (ClCH 2 CH 2 Cl) to yield b 90% dimethyl homoheptalene-4,5-dicarboxylate (3) 2 ) (Scheme 1) [5]. Apart from the specific case of benzo[b...

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Formation of Unusual Products from the Acid-Catalyzed Reaction of Azulenes with Dimethyl Acetylenedicarboxylate

Cited by 5 publications

References 0 publications

New Products from the Heptalene-Forming Reaction of Azulenes and Acetylenedicarboxylates in Polar Media

New Products from the Heptalene-Forming Reaction of Azulenes and Acetylenedicarboxylates in Polar Media

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

New Results in Homoheptalene Chemistry

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