58151-01-2Relevant academic research and scientific papers
187. Double-bond shifts in [4n]annulenes as a new principle for molecular switches: First results with dimethyl heptalene-1,2- and -4,5-dicarboxylates
Briquet, Anne Andree Sophie,Uebelhart, Peter,Hansen, Hans-Juergen
, p. 2282 - 2315 (1996)
A new concept for molecular switches, based on thermal or photochemical double-bond shifts (DBS) in [4n]annulenes such as heptalenes or cyclooctatetraenes, is introduced (cf. Scheme 2). Several heptalene-1,2- and -4,5-dicarboxylates (cf. Scheme 4) with (E)-styryl and Ph groups at C(5) and C(1), or C(4) and C(2), respectively, have been investigated. Several X-ray crystal-structure analyses (cf. Figs. 1-5) showed that the (E)-styryl group occupies in the crystals an almost perfect s-trans-conformation with respect to the C=C bond of the (E)-styryl moiety and the adjacent C=C bond of the heptalene core. Supplementary 1H-NOE measurements showed that the s-trans-conformations are also adopted in solution (cf. Schemes 6 and 9). Therefore, the DBS process in heptalenes (cf. Schemes 5 and 8) is always accompanied by a 180° torsion of the (E)-styryl group with respect to its adjacent C=C bond of the heptalene core. The UV/VIS spectra of the heptalene-1,2- and -4,5-dicarboxylates illustrated that it can indeed be differentiated between an 'off-state', which possesses no 'through-conjugation' of the π-donor substituent and the corresponding MeOCO group and an 'on-state' where this 'through-conjugation' is realized. The 'through-conjugation', i.e., conjugative interaction via the involved s-cis-butadiene substructure of the heptalene skeleton, is indicated by a strong enhancement of the intensities of the heptalene absorption bands I and II (cf. Tables 3-6). The most impressive examples are the heptalene-dicarboxylates 11a, representing the off-state, and 11b which stands for the on-state (cf. Fig.8).
Surprising formation of highly substituted azulenes on thermolysis of 4,5,6,7,8-pentamethyl-2h-eyelohepta[b]furan-2-one and heptalene formation with the new azulenes
Lellek, Vit,Hansen, Hans-Juergen
, p. 1712 - 1736 (2007/10/03)
Heating of 4,5,6,7,8-pentamethyl-2H-cyclohepta[b]furan-2-one (1a) in decalin at temperatures > 170° leads to the development of a blue color, typical for azulenes. It belongs, indeed, to two formed azulenes, namely 4,5,6,7,8-pentamethyl-2-(2,3,4,5,6-pentamethylphenyl)azulene (4a) and 4,5,6,7,8-pentamethylazulene (5a) (cf. Scheme 2 and Table 1). As a third product, 4,5,6,7-tetramethyl-2-(2,3,4,5,6-pentamethylphenyl)-1H-indene (6a) is also found in the reaction mixture. Neither 4,6,8-trimethyl-2H-cyclohepta[b]furan-2-one (1b) nor 2Hcyclohepta[b]furan-2-one (1c) exhibit, on heating, such reactivity. However, heating of mixtures 1a/1b or 1a/1c results in the formation of crossed azulenes, namely 4,6,8-trimethyl-2-(2,3,4,5,6-pentamethylphenyl)azulene (4ba) and 2-(2,3,4,5,6-pentamethylphenyl)azulene (4ca), respectively (cf. Scheme 3). The formation of small amounts of 4,6,8-trimethylazulene (5ba) and azulene (5ca), respectively, besides 1H-indene 6a is also observed. The observed product types speak for an [8 + 2]-cycloaddition reaction between two molecules of la or between 1b and 1c, respectively, with 1a, whereby la plays in the latter two cases the part of the two-atom component (cf. Figs. 5-7 and Schemes 4-6). Strain release, due to the five adjacent Me groups in 1a, in the [8+2]cycloaddition step seems to be the driving force for these transformations (cf. Table3), which are further promoted by the consecutive loss of two molecules of CO2 and concomitant formation of the 10π-electron system of the azulenes. The new azulenes react with dimethyl acetylenedicarboxylate (ADM) to form the corresponding dimethyl heptalene-4,5-dicarboxylates 20, 22, and 24 (cf. Scheme 7), which give thermally or photochemically the corresponding double-bond-shifted (DBS) isomers 20′, 22′, and 24′, respectively. The five adjacent Me groups in 20/20′ and 24/24′ exert a certain buttressing effect, whereby their thermal DBS process is distinctly retarded in comparison to 22/22′, which carry 'isolated' Me groups at C(6), C(8), and C(10). This view is supported by X-ray crystal-structure analyses of 22 and 24 (cf Fig. 8 and Table 5).
Thermal and Ru-catalyzed Reactions of Styryl-Substituted Azulenes with Dimethyl Acetylenedicarboxylate
Briquet, Anne Andree Sophie,Hansen, Hans-Juergen
, p. 1940 - 1968 (2007/10/02)
The thermal reaction of 1-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-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-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-1azulene ((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-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-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).
