AK-2288GP_published_mainmanuscript

AK-2288GP_published_mainmanuscript - Issue in Honor of...

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Issue in Honor of Prof. Alain Krief ARKIVOC 2007 (x) 245-259 Asymmetric synthesis of 4 H -1,3-dioxins and investigations in the metal catalyzed aziridination: aziridination versus insertion and stereoselective course Susanne Flock and Herbert Frauenrath* Institute for Chemistry, University of Kassel, Heinrich-Plett-Straße 40, D-34132 Kassel, Germany E-mail: frauenrath@uni-kassel.de Dedicated to Prof. Alain Krief on his 65 th birthday Abstract The asymmetric synthesis of highly enantiomerically enriched 5-methyl-4 H -1,3-dioxins by DIOP- and DuPHOS-modified nickel complexes via double-bond isomerization and metal catalyzed nitrogen transfer reactions to the resulting dioxins are reported. While Rh catalysis in the reaction of dioxins with nitrenes generated from PhI=NTs afforded insertion products 5 , the Cu(I) catalyzed reactions led to 4-methyl-1,3-oxazolidine-4-carbaldehydes 4 in an aziridination- rearrangement process with diastereoselectivities up to 73% de. Enantiomerically pure aldehydes 4 were obtained by crystallization of the diastereomeric mixture from TBME. A method for the determination of the diastereomeric excess in the intermediate aziridination step is described, and the absolute configurations of the ( S , S )- and ( R , R )-isomer, respectively, were established by X- ray crystallography. Keywords: Asymmetric catalysis, isomerization, dioxins, aziridination, rearrangement, oxazolidinecarbaldehydes Introduction Aziridines, nitrogen analogues of epoxides, 1 have attracted great interest to chemists for years because of their easy transformation into pharmacological and biological active compounds, 2 their appearance as structural subunits in naturally occurring substances, 3 their antitumor and antibiotic activity, 4 or their use as precursors for chiral ligands, building blocks etc. 5 A variety of methods have been developed for the synthesis of aziridines. 6 Among them, metal catalyzed nitrogen transfer processes to alkenes, 7,8 particularly metal catalyzed aziridinations using [ N -(arenesulfonyl)imino]phenyliodinanes as nitrogen sources, 9 have intensively been studied. 10 To obtain optimal yields, these reactions are often performed with a ISSN 1424-6376 Page 245 © ARKAT-USA, Inc.
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Issue in Honor of Prof. Alain Krief ARKIVOC 2007 (x) 245-259 large excess of alkenes, and they are also often accompanied by insertion of a nitrene into activated C-H bonds. 8q,11 More recently, the in situ generation of PhI=NTs and [ N - (alkenesulfonyl)imino]phenyliodinanes have been reported, which avoid the tedious preparation of PhI=NTs 12 and extend the scope of this type of aziridination. 13 In contrast to the aziridination of substituted alkenes, less is known about metal catalyzed nitrogen transfer processes to functionalized alkenes, e.g. enol ethers, glucals, silylketene acetals and others.
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AK-2288GP_published_mainmanuscript - Issue in Honor of...

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