TY - JOUR A1 - Schultze, Christiane A1 - Schmidt, Bernd T1 - Functionalized Benzofurans via Microwave-Promoted Tandem Claisen-Rearrangement/5-endo-dig Cyclization JF - Journal of heterocyclic chemistry N2 - Ortho-allyloxy alkinyl benzenes undergo, upon microwave irradiation in dimethylformamide, a tandem sequence of Claisen-rearrangement and 5-endo-dig cyclization to furnish 7-allyl-substituted benzofurans. With terminal alkynes, chroman-4-ones and enaminoketones become the main products. A mechanistic proposal for this observation relies on a reaction of the starting material with the solvent dimethylformamide under the microwave conditions. Y1 - 2019 U6 - https://doi.org/10.1002/jhet.3671 SN - 0022-152X SN - 1943-5193 VL - 56 IS - 9 SP - 2619 EP - 2629 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Schmidt, Bernd A1 - Nave, Stefan T1 - Stereoselective syntheses of enantiomerically pure 2,5-disubstituted dihydropyrans based on olefin metathesis JF - The journal of organic chemistry N2 - A short synthesis of 2,5-disubstituted dihydropyrans starting from D-mannitol as a chiral building block is described. Our synthetic approach combines ruthenium-catalyzed ring closing olefin metathesis and palladium-catalyzed nucleophilic substitution. Y1 - 2006 U6 - https://doi.org/10.1021/jo061190k SN - 0022-3263 VL - 71 IS - 19 SP - 7364 EP - 7369 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Paz, Cristian A1 - Heydenreich, Matthias A1 - Schmidt, Bernd A1 - Vadra, Nahir A1 - Baggio, Ricardo T1 - Three new dihydro-beta-agarofuran sesquiterpenes from the seeds of Maytenus boaria JF - Acta Crystallographica Section C N2 - As part of a project studying the secondary metabolites extracted from the Chilean flora, we report herein three new beta-agarofuran sesquiterpenes, namely (1S,4S,5S,6R,7R,8R,9R,10S)-6-acetoxy-4,9-dihydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b] oxepine-5,10-diylbis(furan-3-carboxylate), C27H32O11, (II), (1S,4S,5S,6R,7R,9S,10S)-6-acetoxy-9-hydroxy-2,2,5a, 9-tetramethyloctahydro-2H-3,9a-methanobenzo[ b] oxepine-5,10-diyl bis(furan-3-carboxylate), C27H32O10, (III), and (1S,4S,5S,6R,7R,9S,10S)-6-acetoxy-10-(benzoyloxy)-9-hydroxy-2,2,5a,9-tetramethyloctahydro-2H-3,9a-methanobenzo[b]oxepin-5-yl furan-3-carboxylate, C29H34O9, (IV), obtained from the seeds of Maytenus boaria and closely associated with a recently published relative [Paz et al. (2017). Acta Cryst. C73, 451-457]. In the (isomorphic) structures of (II) and (III), the central decalin system is esterified with an acetate group at site 1 and furoate groups at sites 6 and 9, and differ at site 8, with an OH group in (II) and no substituent in (III). This position is also unsubstituted in (IV), with site 6 being occupied by a benzoate group. The chirality of the skeletons is described as 1S, 4S, 5S, 6R, 7R, 8R, 9R, 10S in (II) and 1S, 4S, 5S, 6R, 7R, 9S, 10S in (III) and (IV), matching the chirality suggested by NMR studies. This difference in the chirality sequence among the title structures (in spite of the fact that the three skeletons are absolutely isostructural) is due to the differences in the environment of site 8, i.e. OH in (II) and H in (III) and (IV). This diversity in substitution, in turn, is responsible for the differences in the hydrogen-bonding schemes, which is discussed. KW - Celastraceae KW - Maytenus boaria KW - sesquiterpene KW - dihydro-beta-agarofuran KW - crystal structure KW - NMR KW - DSC Y1 - 2018 U6 - https://doi.org/10.1107/S2053229618005429 SN - 2053-2296 VL - 74 SP - 564 EP - 570 PB - International Union of Crystallography CY - Chester ER - TY - JOUR A1 - Schmidt, Bernd A1 - Petersen, Monib H. A1 - Braun, Diana T1 - Bidirectional Synthesis of 6-Acetoxy-5-hexadecanolide, the Mosquito Oviposition Pheromone of Culex quinquefasciatus, from a C-2-Symmetric Building Block Using Olefin Metathesis Reactions JF - The journal of organic chemistry N2 - (5R,6S)-6-Acetoxy-5-hexadecanolide (MOP) is the oviposition pheromone of the mosquito Cx. quinquefasciatus, a vector of pathogens causing a variety of tropical diseases. We describe and evaluate herein three syntheses of MOP starting from mannitol-derived (3R,4R)-hexa-1,5-diene-3,4-diol. This C-2-symmetric building block is elaborated through bidirectional olefin metathesis reactions into 6-epi-MOP, which was converted into MOP via Mitsunobu inversion. The shortest of the three routes makes use of two sequential cross-metathesis reactions and an assisted tandem catalytic olefin reduction, induced by an in situ conversion of a Ru-carbene to a Ru-hydride. Y1 - 2018 U6 - https://doi.org/10.1021/acs.joc.7b02944 SN - 0022-3263 VL - 83 IS - 3 SP - 1627 EP - 1633 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sand, Patrick A1 - Schmidt, Bernd T1 - Pd-catalyzed oxidative sulfoalkenylation of acetanilides and traceless removal of the catalyst directing group JF - ChemistrySelect N2 - The palladium-catalyzed oxidative Heck-reaction, also referred to as Fujiwara-Moritani-reaction, has been investigated for the synthesis of styrenylsulfonyl compounds. Acetanilides and vinylsulfonyl compounds undergo dehydrogenative coupling reactions in moderate to quantitative yields, using benzoquinone as the oxidant of choice. Potassium peroxodisulfate, which had previously been identified as a superior oxidant for the coupling with acrylates, did not provide any coupling products with these olefins. Traceless removal of the catalyst directing group through a deacetylation-diazotation-coupling (DDC) sequence was demonstrated for 2-arylethene sulfones. KW - arenes KW - C− H activation KW - Heck reactions KW - Palladium KW - sulfones Y1 - 2021 U6 - https://doi.org/10.1002/slct.202101009 SN - 2365-6549 VL - 6 IS - 14 SP - 3563 EP - 3567 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Lood, Kajsa A1 - Schmidt, Bernd T1 - Stereoselective synthesis of conjugated polyenes based on tethered olefin metathesis and carbonyl olefination BT - application to the total synthesis of (+)-bretonin B JF - The journal of organic chemistry N2 - The combination of a highly stereoselective tethered olefin metathesis reaction and a Julia-Kocienski olefination is presented as a strategy for the synthesis of conjugated polyenes with at least one Z-configured C=C bond. The strategy is exemplified by the synthesis of the marine natural product (+)-bretonin B. KW - absolute-configuration KW - natural-products KW - formal synthesis KW - oxidation KW - derivatives KW - aldehydes KW - catalysts KW - alcohols KW - sponge KW - ethers Y1 - 2020 U6 - https://doi.org/10.1021/acs.joc.0c00446 SN - 0022-3263 SN - 1520-6904 VL - 85 IS - 7 SP - 5122 EP - 5130 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schultze, Christiane A1 - Foß, Stefan A1 - Schmidt, Bernd T1 - 8-Prenylflavanones through microwave promoted tandem claisen rearrangement/6-endo-trig cyclization and cross metathesis JF - European journal of organic chemistry N2 - Prenylated flavanones were obtained from ortho-allyloxy chalcones through a one-pot sequence of Claisen rearrangement and 6-endo-trig cyclization, followed by olefin cross metathesis of the intermediate allyl flavanones with 2-methyl-2-butene. The synthetic utility of this route is illustrated for the synthesis of several naturally occurring prenyl flavanones. KW - tandem reactions KW - arenes KW - oxygen heterocycles KW - microwave chemistry KW - rearrangement Y1 - 2020 U6 - https://doi.org/10.1002/ejoc.202001378 SN - 1434-193X SN - 1099-0690 VL - 2020 IS - 47 SP - 7373 EP - 7384 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Lood, Kajsa A1 - Tikk, Triin A1 - Krüger, Mandy A1 - Schmidt, Bernd T1 - Methylene capping facilitates cross-metathesis reactions of enals BT - a short synthesis of 7-methoxywutaifuranal from the xylochemical isoeugenol JF - The journal of organic chemistry N2 - Four combinations of type-I olefins isoeugenol and 4-hydroxy-3-methoxystyrene with type-II olefins acrolein and crotonaldehyde were investigated in cross-metathesis (CM) reactions. While both type-I olefins are suitable CM partners for this transformation, we observed synthetically useful conversions only with type-II olefin crotonaldehyde. For economic reasons, isoeugenol, a cheap xylochemical available from renewable lignocellulose or from clove oil, is the preferred type-I CM partner. Nearly quantitative conversions to coniferyl aldehyde by the CM reaction of isoeugenol and crotonaldehyde can be obtained at ambient temperature without a solvent or at high substrate concentrations of 2 mol.L-1 with the second-generation Hoveyda-Grubbs catalyst. Under these conditions, the ratio of reactants can be reduced to 1:1.5 and catalyst loadings as low as 0.25 mol % are possible. The high reactivity of the isoeugenol/crotonaldehyde combination in olefin metathesis reactions was demonstrated by a short synthesis of the natural product 7-methoxywutaifuranal, which was obtained from isoeugenol in a 44% yield over five steps. We suggest that the superior performance of crotonaldehyde in the CM reactions investigated can be rationalized by "methylene capping", i.e., the steric stabilization of the propagating Ru-alkylidene species. KW - Aldehydes KW - Catalysts KW - Hydrocarbons KW - Metathesis KW - Mixtures Y1 - 2022 U6 - https://doi.org/10.1021/acs.joc.1c02851 SN - 0022-3263 SN - 1520-6904 VL - 87 IS - 5 SP - 3079 EP - 3088 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Hermanns, Jolanda A1 - Schmidt, Bernd A1 - Glowinski, Ingrid A1 - Keller, David T1 - Online teaching in the course "organic chemistry" for nonmajor chemistry students BT - from necessity to opportunity JF - Journal of chemical education N2 - In this communication the development of an online course on the topic organic chemistry for nonmajor chemistry students is described and discussed. For this online course, the existing classroom course was further developed. New elements such as podcasts, task navigators, and a forum for discussing the solving of tasks or problems with the content were added. This new online course was evaluated. Therefore, a questionnaire was developed. This consists of questions with regard to the longtime learning behavior of the students and to the online learning. The results of this evaluation show that a preference for online learning and a preference for classroom teaching can be measured separately in two scales. Students values on the scale representing a preference for online learning correlate positively and significantly with confidence in the choice of the study subject, enthusiasm about the subject, and the ability to organize their learning, learning environment, and time management. They correlate also with the satisfaction concerning the materials provided. Students values for one of those teaching methods also correlate with their rating with regard to their exam preparation. Values representing a preference for online teaching correlate positively with students better feeling of exam preparation. Values representing a preference for classroom teaching show negative correlations with the values representing students similar or even better preparation for the exams as a result of online teaching. It is therefore not surprising that the ratings for the two scales correlate with the wish for a combination of online teaching and classroom teaching in the future. As a solution, a new course concept for the time after the corona virus crisis that suits all students is outlined in the outlook. KW - first-year undergraduate/general KW - organic chenlistry KW - computer-based KW - learning KW - distance learning/self instruction Y1 - 2020 U6 - https://doi.org/10.1021/acs.jchemed.0c00658 SN - 0021-9584 SN - 1938-1328 VL - 97 IS - 9 SP - 3140 EP - 3146 PB - American Chemical Society CY - Washington ER - TY - BOOK A1 - Buddrus, Joachim A1 - Schmidt, Bernd T1 - Grundlagen der organischen Chemie Y1 - 2015 SN - 978-3-11-030559-3 PB - de Gruyter CY - Berlin ET - 5., überarb. und aktualisierte Aufl. ER -