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31.
Contrary to the rearrangement of 3-amino-3-X-propenals, which easily gives 3-X-propenamides at low temperature, the postulated rearrangement (Scheme 1) of the vinylogous 5-amino-5-X-pentadienals 2 normally stops at the level of (2H-pyran-2-ylidene)ammonium salts 4 . The main reason is that salts of type 4 are highly delocalized low-energy, charged species which makes addition 4 → 5 of weak nucleophiles difficult. In this paper, the first examples of the so-called `aminopentadienal' rearrangement are reported. Ring-opening 4 → 6 is facilitated by nucleophilic counter ions like X=PhO (see Scheme 4) or by adding an excess of `nucleophilic auxiliaries' such as Et3N or EtOH (see Scheme 2). In a quite interesting sequence of steps, 5-phenoxy-5-(pyrrol-1-yl)penta-2,4-dienal ( 2g ; X=PhO) is easily transformed into 5H-pyrrolo[1,2-a]azepin-5-one ( 9 ) (Scheme 5). 相似文献
32.
Christopher J. Burns Robert D. Groneberg Joseph M. Salvino Gerard McGeehan Stephen M. Condon Robert Morris Matthew Morrissette Rose Mathew Shelley Darnbrough Kent Neuenschwander Anthony Scotese Stevan W. Djuric John Ullrich Richard Labaudiniere 《Angewandte Chemie (International ed. in English)》1998,37(20):2848-2850
One common synthetic route creates small-molecule libraries directed toward two functionally distinct target families. The novel structural template 1 can independently display the necessary pharmacophore patterns for inhibition of members of two different biomolecular target families, the matrix metalloproteinases (MMPs) or the phosphodiesterases (PDEs). The incorporation of multiple target family directed design elements into combinatorial library design could help expedite the pharmaceutical lead discovery process. Z=OR′ (PDE4), H (MMPs). 相似文献
33.
In view of possible applications of `push-pull' acetylenes 1 and `push-pull' olefins 2 as potential non-linear optics materials, synthetic attempts towards polymers of type 4 and 6 (Scheme 2) have been undertaken. Two so far unknown `push-pull' acetylenes 1a , b with R=styrene, have been prepared under carefully controlled conditions which quite surprisingly fail to give polymers 4a , b by anionic or radical-induced polymerization. On the other hand, `push-pull' acetylenes may be reacted with commercially available poly(4-vinylphenol) to give polymers 6c , d with a 40 – 70% conversion of phenol units. 相似文献
34.
35.
Synthesis of a Calicene Precursor for Retro-Diels-Alder Reactions In view of retro-Diels-Alder reactions (RDA reactions), the calicene precursor 9 has been synthesized in a comparably simple four-step synthesis by dibromocarbene addition at dibenzobarrelene ( 10 → 11 , 44%), halogenlithium exchange followed by reaction with cyclopentenone ( 11→12 , 91%) and H2O as well as HBr elimination ( 12→14→9 , 43%) (Scheme 5). First experiments with respect to the thermal behavior of 9 show that, although RDA reaction seems to be relatively easily occurring according to the results of ‘Curie-Point’ pyrolysis, only anthracene and no calicene 2 has been detected so far. 相似文献
36.
Jürg Krebs Dominik Guggisberg Urs Stmpfli Markus Neuenschwander 《Helvetica chimica acta》1986,69(4):835-848
Synthesis of Triafulvene Precursors for Retro-Diels-Alder Reactions Triafulvene precursors exo? 15 and endo? 15 have been prepared by addition of dibromocarbene to benzobarrelene 12 followed by a lithium-halogen exchange, methylation, and elimination of HBr ( 12→13→14→15 ), (Scheme 2). Gas-phase pyrolysis of exo/endo-mixtures of 15 above 400° gave minor amounts of naphthalene ( 16 ), traces of a hydrocarbon C4H4 identified by MS (presumably triafulvene 1 ) and predominantly (36%) the isomerization product 17 (Scheme 3). In a second synthetic approach the well-known cycloheptatriene-norcaradiene equilibrium of type 26?27 has been utilised to prepare various endo-trans-3-(X-methyl) tricyclo[3.2.2.02,4]nona-6,8-dienes 31 (Scheme 5). However, numerous elimination experiments 31→9 failed so far. The structure of two rearrangement products 33 and 34 (Scheme 6) has been elucidated. 相似文献
37.
1H- and 13C-NMR spectra of a series of 8-R1-substituted as well as of 8,8-R1, R2-disubstituted heptafulvenes, varying from inversely polarized ( 3l ) to unpolar ( 3h ) and polar heptafulvenes with electron-withdrawing groups ( 3d , e , f ), have been analyzed and compared with those of methoxytropylium salt 5a . The results concerning 3J (H,H) values and 13C-chemical shifts are shown in Figs. 5 and 6. It turns out that all the NMR parameters are strongly influenced by substituents R1, R2, but contrary to planar pentafulvenes, no linear correlations of the NMR parameter vs. Hammett substituent constant σ+ are obtained in the series 3l → 3d . 3J coupling constants J(2,3)/J(4,5) and J(3,4) are not much influenced by substituent changes in the series 3l → 3h , but are approaching in the row 3h → 3d . Similarly, signals of the 13C-atoms undergo a moderate shift to higher frequencies in the row 3l → 3h , but are strongly influenced by ? M groups, whereby the sensitivity is decreasing in the series C(7) > C(2)/C(5) > C(3)/C(4) > C(1)/C(6). These results are essentially explained by a boat conformation of inversely polarized heptafulvenes of the type 3l and an increasing planarization of the ring on going to polar heptafulvenes of type 3d . 相似文献
38.
With the aim to investigate the influence of structural isomerism on the mesomorphic thermal stability in main chain thermotropic polycondensates, a series of poly(azomethines) and low molecular weight models have been prepared. The model compounds exhibit smectic and/or nematic mesophases whose stabilites are very sensitive to structural modifications. On the basis of the above results, monomers 2, 5, 6, 8, 9, 23, 25 , and 26 were selected to synthesize oligomers 27–23 . The oligomer 33 obtained from the nonsymmetric diamine 23 has a lower melting point than the symmetric oligomer 28 , but a similar liquid crystalline range. 相似文献
39.
Reaction of ‘Push-Pull’ Enynes with Acids. First Observation of a Rearrangement of 5-Chloro-5-(dialkylamino)pentadienals ‘Push-pull’-enynes 7 react easily with HCl as well as with AcOH to give 5-amino-5-chloropentadienals 8 and 5-(acetoxy)-5-aminopentadienals 13 as well as the corresponding ketones. In view of a postulated rearrangement of compounds 8 and 13 (Scheme 2), both types of compounds have been treated with traces of acid. While no definite reaction is observed in case of 13 , HCl-addition products 8 easily and quantitatively rearrange to give 2H-pyran-2-iminium chlorides 10 which are the postulated intermediates of the rearrangement 8 → 12 (Scheme 2). 相似文献
40.
Synthesis and Pyrolysis of a Triafulvene Precursor In view of retro-Diels-Alder reactions (RDA reactions), the triafulvene precursor 3 has been prepared in a simple three-step synthesis by dibromocarbene addition at dibenzo-barrelene ( 11→12 ; 44%), halogen-Li exchange followed by methylation ( 12→14 , 100%) and HBr elimination ( 14→3 , 62%) (Scheme 3). Reactivity of the so far unknown bridged 1,1-dibromocyclopropane 12 has been explored, including reductions, allylic rearrangements, and ‘carbene dimerizations’ (Scheme 4). First experiments with respect to the thermal behavior of 3 show that RDA reaction, although occurring in most cases, is not the predominant pathway. When 3 is heated in a sealed tube without solvent, two dimers 26 and 27 are isolated in a total yield of 55% (Scheme 6). On the other hand, gas-phase pyrolysis of 3 at 400° mainly produces rearranged 28 (56%; Scheme 7). It is assumed that bridged trimethylenemethane 29 is an essential intermediate in thermal rearrangements of 3 (Scheme 8). 相似文献