Here, aiming to adopt the phenyl–perfluorophenyl interaction to regulate molecular alignment and arrangement for crystal engineering, we examined and compared in detail the crystal structures of N,N′-diphenylurea compounds 1–6. We found that phenyl–perfluorophenyl interaction greatly influenced the intermolecular arrangement in the crystal, and we were able to prepare a cocrystal of 1 and 2, in which the molecules were alternately arranged under the control of the phenyl–perfluorophenyl interaction. This arrangement was driven by the asymmetric geometry of the hydrogen bonds in the cocrystal (1·2), in which 2, bearing two perfluorophenyl groups, worked as a better hydrogen bond donor. In contrast, NH connected to the phenyl group in 3 proved to be a better hydrogen bond donor due to the intramolecular resonance effect. N,N′-Dimethylated derivatives, 4–6, existed in cis-cis form in the crystal. Antiparallel carbonyl–carbonyl arrangements were observed in 4 and 6, while an unexpected carbonyl–perfluorophenyl interaction was observed in the crystal of 5. These findings will be helpful in the design of diphenylurea-based functional molecules, especially for solid-state application.

Activated amide bonds have been attracting intense attention; however, most of the studied moieties have twisted amide character. To add a new strategy to activate amide bonds while maintaining its planarity, we envisioned the introduction of an alkynyl group on the amide nitrogen to disrupt amide resonance by nN→Csp conjugation. In this context, the conformations and properties of N‐ethynyl‐substituted aromatic amides were investigated by DFT calculations, crystallography, and NMR spectroscopic analysis. In contrast to the cis conformational preference of N‐ethyl‐ and vinyl‐substituted acetanilides, N‐ethynyl‐substituted acetanilide favors the trans conformation in the crystal and in solution. It also has a decreased double bond character of the C(O)−N bond, without twisting of the amide. N‐Ethynyl‐substituted acetanilides undergo selective C(O)−N bond or N−C(sp) bond cleavage reactions and have potential applications as activated amides for coupling reactions or easily cleavable tethers.

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Amide-based molecular switches had its limitation on structural diversities. In this work, we designed and synthesized a series of pentafluorobenzoyl-based benzanilide compounds. The conformational ratio of these compounds in solution was correlated linearly with Hammett's σ p value of the substituent on the anilide ring, reflecting the repulsive interaction between the carbonyl group and the electron-rich aryl group. The addition of acid into the solution of 6, bearing pentafluorobenzoyl group, switched the stable amide conformation. In addition, the sizeable rotational barrier of 6 induced by the pentafluorobenzoyl moiety enabled us to monitor the conformational transition by means of 1 H NMR spectroscopy.

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The Diels-Alder (D-A) reaction is one of the most useful reactions in synthetic organic chemistry. Recently, we reported that thiocarbonyl compounds 2, 4, and 6 yielded dienes 3, 5, and 7, respectively, through alkylation reactions, and these dienes underwent Diels-Alder reaction with appropriate dienophiles to give functionalized carbazoles, indoles, and benzene derivatives.1-3) Previously, we found that 4-thioxo-4,5,6,7-tetrahydroindole 8, having a thioenaminone moiety, gave dehydrochuangxinmycin through alkylation. 4)We also found that the cycloaddition reaction of N-methyl-3-vinylpyrrole 5 proceeded smoothly, whereas the NH congener 9 gave no cycloaddition product. This may be due to the lability of vinylpyrrole 10, and the result was not investigated further.This paper describes an improved synthesis of sulfur substituted 3-vinylpyrroles 10 and their application to the syntheses of chuangxinmycin having various substituents. In 1978, E. J. Cory et al. reported the utility of intramolecular Diels-Alder reaction using propylene oxide as a hydrogen chloride scavenger in the synthesis of gibberellic acid.5) The application of propylene oxide as a scavenger prompted us to examine its use in the preparation of 3-vinylpyrrole 10 from 3-thioacetylpyrrole 9 and alkyl halide. A preliminary study was done on the reaction of 10a, generated in situ by the reaction of 3-thioacetylpyrrole 9 with methyl iodide in the presence of a large excess of propylene oxide, with dimethyl acetylenedicarboxylate (DMAD) in tetrahydrofuran (THF). The indole 11a was indeed obtained in 20% overall yield. Similarly, the reactions of 10b and 10c, generated in situ with benzyl bromide and methyl bromoacetate, with DMAD, gave the indoles 11b and 11c, in 17.2 and 27.3% yields respectively. Figure 2 proposes a possible mechanism for the generation of dienes 10. Reaction of the diene 10c with Nmethylmaleimide at 110°C for 8 h, followed by treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) for 30 min, gave the indole 12a in 27.3% yield. Similarly, the reaction of the diene 10c with 3,4-dibromo-N-methylmaleimide in THF at room temperature for 8 h, followed by direct in situ oxidation, gave 12a in 36.5% yield.In general, the cycloaddition reaction of vinylpyrroles 10 with dienophiles were carried out in a fused glass tube at 100°C under nitrogen for approximately 8 h. The results are summarized in Table 1. The indoles 11c and 12a are the key intermediates in the syntheses of substituted chuangxinmycin derivatives.Synthesis of 7,8-Disubstituted Chuangxinmycin Derivatives Chuangxinmycin 1, isolated from the microorganism Actinoplanes tsinanensis n. sp. of China, 6) is an antibiotic alkaloid bearing a sulfur substituent at the 4-position of the indole nucleus. This compound is known to be active against a variety of Gram-positive and Gram-negative bacteria and is particularly effective in the treatment of Escherichia coli infections. 7)Total synthesis of 1 has already been reported by several groups.8) We also have reported two routes of fo...