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121.
Harrison M. Bergman D. Dawson Beattie Gavin R. Kiel Rex C. Handford Yi Liu T. Don Tilley 《Chemical science》2022,13(19):5568
The synthesis of polycyclic aromatic hydrocarbons (PAHs) and related nanographenes requires the selective and efficient fusion of multiple aromatic rings. For this purpose, the Diels–Alder cycloaddition has proven especially useful; however, this approach currently faces significant limitations, including the lack of versatile strategies to access annulated dienes, the instability of the most commonly used dienes, and difficulties with aromatization of the [4 + 2] adduct. In this report we address these limitations via the marriage of two powerful cycloaddition strategies. First, a formal Cp2Zr-mediated [2 + 2 + 1] cycloaddition is used to generate a stannole-annulated PAH. Secondly, the stannoles are employed as diene components in a [4 + 2] cycloaddition/aromatization cascade with an aryne, enabling π-extension to afford a larger PAH. This discovery of stannoles as highly reactive – yet stable for handling – diene equivalents, and the development of a modular strategy for their synthesis, should significantly extend the structural scope of PAHs accessible by a [4 + 2] cycloaddition approach.Stannoles are introduced as a new, spontaneously aromatizing diene for [4 + 2] cycloadditions that can be easily introduced into diverse conjugated systems, facilitating the efficient synthesis of complex PAHs and their π-extension. 相似文献
122.
Franziska A. Klapper Dr. Christine Kiel Dr. Peter Bellstedt Prof. Dr. Wim Vyverman Prof. Dr. Georg Pohnert 《Angewandte Chemie (International ed. in English)》2023,62(43):e202307165
Diatoms are abundant unicellular microalgae, responsible for ≈20 % of global photosynthetic CO2 fixation. Nevertheless, we know little about fundamental aspects of their biology, such as their sexual reproduction. Pheromone-mediated chemical communication is crucial for successful mating. An attraction pheromone was identified in the diatom Seminavis robusta, but metabolites priming cells for sex and synchronizing search and mating behavior remained elusive. These sex-inducing pheromones (SIP) induce cell cycle arrest and trigger the production of the attraction pheromone. Here we describe the challenging structure elucidation of an S. robusta SIP. Guided by metabolomics, a candidate metabolite was identified and elucidated by labeling experiments, NMR, ESI MSn analyses, and chemical transformations. The use of negative ion mode MS was essential to decipher the unprecedented hydroxyproline and β-sulfated aspartate-containing cyclic heptapeptide that acts in femtomolar concentrations. 相似文献
123.
Seung Jun Han Mi Kyong Yoo Yong Kiel Sung Young Moo Lee Chong Su Cho 《Macromolecular rapid communications》1998,19(8):403-407
Polymerization of N-isopropylacrylamide (NIPAAm) was performed in the presence of β-cyclodextrin (β-CD) [or hydroxypropyl-β-cyclodextrin (HOP-β-CD)]. The formation of an inclusion complex between PNIPAAm and β-CD was confirmed by FT-IR, 1H NMR and 2D-NOESY NMR. It was found that the cloud point (CP) of poly(N-isopropylamide) (PNIPAAm) in the PNIPAAm/β-CD complex in aqueous solution increased up to about 57°C whereas that in the PNIPAAm/β-CD blend is about 33°C. The CP of PNIPAAm in the PNIPAAm/β-CD complex is higher than that in the PNIPAAm/HOP-β-CD inclusion complex. IR and NMR results suggest that PNIPAAm chains are included in CD cavities. 相似文献