TY - JOUR A1 - Schmidt, Bernd A1 - Schultze, Christiane T1 - A one-pot synthesis of pyranocoumarins through microwave-promoted propargyl claisen rearrangement/wittig olefination JF - European journal of organic chemistry N2 - The reaction between propargyl ethers of hydroxybenzaldehydes and the ylide ethyl (triphenylphosphoranylidene)acetate was carried out under microwave irradiation to regioselectively afford angular pyranocoumarins. The chromene and coumarin heterocyclic scaffolds were simultaneously formed in the same synthetic step without changing the reaction conditions. The natural products seselin, braylin, and dipetalolactone were among the products synthesized by this method. KW - Domino reactions KW - Alkynes KW - Arenes KW - Oxygen heterocycles KW - Microwave chemistry KW - Rearrangement Y1 - 2017 SN - 1434-193X SN - 1099-0690 VL - 2018 IS - 2 SP - 223 EP - 227 PB - Wiley-VCH Verl. CY - Weinheim 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 - 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 - Schultze, Christiane A1 - Schmidt, Bernd T1 - Prenylcoumarins in One or Two Steps by a Microwave-Promoted Tandem Claisen Rearrangement/Wittig Olefination/Cyclization Sequence JF - The journal of organic chemistry N2 - The one-pot synthesis of 8-prenylcoumarins from 1,1-dimethylallylated salicylaldehydes and the stabilized ylide [(ethoxycarbonyl)methylene]triphenylphosphorane under microwave conditions was found to have a limited scope. The sequence suffers from a difficult and sometimes low-yielding synthesis of the precursors and from a competing deprenylation upon microwave irradiation. This side reaction occurs in particular with electron rich arenes with two or more alkoxy groups at adjacent positions, a prominent substitution pattern in naturally occurring 8-prenylcoumarins. Both limitations of this one-step sequence were overcome by a two-step synthesis consisting of a microwave-promoted tandem allyl ether Claisen rearrangement/Wittig olefination and a subsequent olefin cross metathesis with 2-methyl-2-butene. The cross metathesis step proceeds with a high selectivity and yields exclusively the desired prenyl, rather than the alternative crotyl substituent. Several naturally occurring 8-prenylcoumarins that were previously inaccessible have been synthesized in good overall yields along this route. Y1 - 2018 U6 - https://doi.org/10.1021/acs.joc.8b00667 SN - 0022-3263 VL - 83 IS - 9 SP - 5210 EP - 5224 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schultze, Christiane A1 - Schmidt, Bernd T1 - Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins JF - Beilstein journal of organic chemistry N2 - 8-Allylcoumarins are conveniently accessible through a microwave-promoted tandem Claisen rearrangement/Wittig olefination/cyclization sequence. They serve as a versatile platform for the annellation of five- to seven-membered rings using ring-closing olefin metathesis (RCM). Furano-, pyrano-, oxepino- and azepinocoumarins were synthesized from the same set of precursors using Ru-catalyzed double bond isomerizations and RCM in a defined order. One class of products, pyrano[2,3-f]chromene-2,8-diones, were inaccessible through direct RCM of an acrylate, but became available from the analogous allyl ether via an assisted tandem catalytic RCM/allylic oxidation sequence. KW - coumarins KW - heterocycles KW - isomerization KW - olefin metathesis KW - ruthenium Y1 - 2018 U6 - https://doi.org/10.3762/bjoc.14.278 SN - 1860-5397 VL - 14 SP - 2991 EP - 2998 PB - Beilstein-Institut zur Förderung der Chemischen Wissenschaften CY - Frankfurt, Main ER -