188635-46-3Relevant academic research and scientific papers
Synthesis and characterization of new heptalenes with extended π-systems attached to them
Maillefer-El Houar, Sarah,Uebelhart, Peter,Linden, Anthony,Hansen, Hans-Juergen
, p. 1488 - 1541 (2013/09/02)
Methyl heptalenecarboxylates of type A and B with π(1) and π(2) substituents in 1,4-relation (Scheme 1) were synthetized starting with dimethyl 1-methylheptalene-4,5-dicarboxylates 5b and 6b derived from 7-isopropyl-1,4- dimethylazulene (=guaiazulene) and 1,4,6,8-tetramethylazulene by thermal reaction with dimethyl acetylenedicarboxylate. The further general way of proceeding for the introduction of the π(1) and π(2) substituents is displayed in Scheme 3, and the thus obtained methyl heptalene-5-carboxylates of type A and B are listed in Table 1. The C=C bonds of the 2-arylethenyl and 4-arylbuta-1,3-dien-1-yl groups of π(1) and π(2) were in all cases (E)-configured and showed s-trans conformation at the C-C bonds (X-ray and 1H-NOE evidence) in the B-type as well as in the A-type heptalenes (cf. Figs. 5-12). All B-type heptalenes showed a strongly enhanced heptalene band I in the wavelength region 440-490 nm in hexane/CH2Cl 2 9: 1 (cf. Table 4 and Figs. 13-20). The A-type heptalenes showed in this region only weak absorption, recognizable as shoulders or simply tailing of the dominating heptalene bands II/III (Table 5). Absorption band I of the B-type heptalenes appeared almost at the same wavelength as the longest wavelength absorption band of comparable open-chain α,ω- diarylpolyenes (cf. Fig. 21). The cyclic double bond shift (DBS) of the A- and B-type heptalenes could be photochemically steered in one or the other direction by selective irradiation (cf. Fig. 22). Copyright
New Heptalenes Substituted with Extended π-Systems
El Houar, Sarah,Hansen, Hans-Juergen
, p. 253 - 266 (2007/10/03)
The synthesis of π-substituted heptalenecarboxylates or -dicarboxylates, starting with the easily available dimethyl 9-isopropyl-1,6-dimethylheptalene-4,5-dicarboxylate (2b), are described. Treatment of 2b with t-BuOK and C2Cl6 at -78° leads to the chemoselective introduction of a Cl substituent in Me-C(1) (see 5b in Scheme 1). Formation of the corresponding triphenylphosphonium salt 7b via the iodide 6b (Scheme 2) allowed a Wittig reaction with cinnamaldehyde in the two-phase system CH2Cl2/2N NaOH. Transformation of the 4,5-dicarboxylate of 2b into the corresponding pseudo-ester 10b allowed the selective reduction of the carbonyl function at C(4) with DIBAH to yield the corresponding 4-carbaldehyde 11b (Scheme 3). Wittig reaction of 11b with (benzyl)triphenylphosphonium bromide led to the introduction of the 4-phenylbuta-1,3-dienyl substituent at C(4). The combination of both Wittig reactions led to the synthesis of the 1,4-bis(4-phenylbuta-1,3-dienyl)-substituted heptalene-5-carboxylate (all-E)-17b (Scheme 5). In a similar manner, by applying a Horner-Wadsworth-Emmons reaction, followed by the Wittig reaction, the donor-acceptor substituted heptalene-5-carboxylate (E;E)-22b was synthesized (Scheme 7). Most of these new heptalenes are in solution, at room temperature, in thermal equilibrium with their double-bond shifted (DBS) isomers. In the case of (all-E)-17b and (E;E)-22b, irradiation of the thermal equilibrium mixture with light of λ = (439 ± 10) nm led to a strong preponderance (> 90%) of the DBS isomers 17a and (E;E)-22a, respectively (Schemes 6 and 7). Heating of the photo-mixtures at 40° re-established quickly the thermal equilibrium mixtures. Heptalenes-carboxylates (all-E)-17a and (E;E)-22a which represent the off-state of a 1,4-conjugative switch (CS) system show typical heptalene UV/VIS spectra with a bathochromically shifted heptalene band III and comparably weak heptalene bands II and I which appear only as shoulders (Figs. 4 and 5). In contrast, the DBS isomers (all-E)-17b and (all-E)-22b, equivalent to the on-state of a 1,4-CS system, exhibit extremely intense heptalene bands I and, possibly, II which appear as a broad absorption band at 440 and 445 nm, respectively, thus indicating that the CSs (all-E)-17a?(all-E)-17b and (E;E)-22a?(E;E)-22b are perfectly working.
