An efficient, one-pot and metal-free process for the preparation of 3,5-disubstituted and 3,4,5-trisubstituted pyrazoles on multi-gram scale was developed. One-pot condensation of ketones, aldehydes and hydrazine monohydrochloride readily formed pyrazoline intermediates under mild conditions. Oxidation of pyrazolines, in situ, employing bromine afforded a wide variety of pyrazoles. The methodology offers a fast, and often chromatography-free protocol for the synthesis of 3,4,5-substituted pyrazoles in good to excellent yields. Alternatively, a more benign oxidation protocol affords 3,5-disubstituted or 3,4,5-trisubstituted pyrazoles by simply heating pyrazolines in DMSO under oxygen.

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Axially chiral synthons for chiral dendrimer construction based on 2,2′-dihydroxy-1,1′-binaphthalene-3,3′-dicarboxylic acid were prepared, namely, chiral connecting units (3, 6, 8), chiral branching units (10, 12, 14), and chiral surface units (5, 17). Regioselective chloromethylation of methyl 3′-acetoxymethyl-2,2′-dimethoxy-1,1′-binaphthalene-3-carboxylate (7) was also studied.

Dedicated to Edgar Heilbronner on the occasion of his 80th birthday Der Mensch kommt nicht um die Tatsache herum, dass die Sinne zwar als höchste Herren seine Erkenntnisfähigkeit bestimmen, ihm aber keine Sicherheit bieten, da sie in jeder Lage sich leicht täuschen lassen. Michel de Montaigne, Essais (Übers. Hans Stilett)Heating of 4,5,6,7,8-pentamethyl-2H-cyclohepta[b]furan-2-one (1a) in decalin at temperatures b 1708 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,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 1a or between 1b and 1c, respectively, with 1a, whereby 1a 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 . Table 3), which are further promoted by the consecutive loss of two molecules of CO 2 and concomitant formation of the 10p-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).

Dedicated to Conrad Hans Eugster on the occasion of his 80th birthday A number of aryl 3-arylprop-2-ynoates 3 has been prepared (cf. Table 1 and Schemes 3 ± 5). In contrast to aryl prop-2-ynoates and but-2-ynoates, 3-arylprop-2-ynoates 3 (with the exception of 3b) do not undergo, by flash vacuum pyrolysis (FVP), rearrangement to corresponding cyclohepta[b]furan-2(2H)-ones 2 (cf. Schemes 1 and 2). On melting, however, or in solution at temperatures > 1508, the compounds 3 are converted stereospecifically to the dimers 3-[(Z)-diarylmethylidene]-2,3-dihydrofuran-2-ones (Z)-11 and the cyclic anhydrides 12 of 1,4-diarylnaphthalene-2,3-dicarboxylic acids, which also represent dimers of 3, formed by loss of one molecule of the corresponding phenol from the aryloxy part (cf. Scheme 6). Small amounts of diaryl naphthalene-2,3-dicarboxylates 13 accompanied the product types (Z)-11 and 12, when the thermal transformation of 3 was performed in the molten state or at high concentration of 3 in solution (cf. Tables 2 and 4). The structure of the dihydrofuranone (Z)-11c was established by an X-ray crystal-structure analysis (Fig. 1). The structures of the dihydrofuranones 11 and the cyclic anhydrides 12 indicate that the 3-arylprop-2-ynoates 3, on heating, must undergo an aryl O 3 C(3) migration leading to a reactive intermediate, which attacks a second molecule of 3, finally under formation of (Z)-11 or 12. Formation of the diaryl dicarboxylates 13, on the other hand, are the result of the well-known thermal Diels-Alder-type dimerization of 3 without rearrangement (cf. Scheme 7). At low concentration of 3 in decalin, the decrease of 3 follows up to ca. 20% conversion first-order kinetics (cf . Table 5), which is in agreement with a monomolecular rearrangement of 3. Moreover, heating the highly reactive 2,4,6-trimethylphenyl 3-(4-nitrophenyl)prop-2-ynonate (3f) in the presence of a twofold molar amount of the much less reactive phenyl 3-(4-nitrophenyl)prop-2-ynonate (3g) led, beside (Z)-11f, to the cross products (Z)-11fg, and, due to subsequent thermal isomerization, (E)-11fg (cf. Scheme 10), the structures of which indicated that they were composed, as expected, of rearranged 3f and structurally unaltered 3g. Finally, thermal transposition of [ 17 O]-3i with the 17 O-label at the aryloxy group gave (Z)-and (E)-[ 17 O 2 ]-11i with the 17 O-label of rearranged [ 17 O]-3i specifically at the oxo group of the two isomeric dihydrofuranones (cf. Scheme 8), indicating a highly ordered cyclic transition state of the aryl O 3 C(3) migration (cf. Scheme 9).