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Keywords = Boc-protected benzamides

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15 pages, 2581 KiB  
Article
Organocatalytic Asymmetric Halocyclization of Allylic Amides to Chiral Oxazolines Using DTBM-SEGPHOS—Mechanistic Implications from Hammett Plots
by Fotini Moschona, Christina Misirlaki, Nikolaos Karadimas, Maria Koutiva, Ioanna Savvopoulou and Gerasimos Rassias
Symmetry 2022, 14(5), 989; https://doi.org/10.3390/sym14050989 - 12 May 2022
Cited by 1 | Viewed by 4834
Abstract
The intramolecular halocyclization of alkenes possessing an internal heteroatom nucleophile leads to multifunctional heterocycles which are useful versatile intermediates in organic synthesis. The asymmetric chlorocyclisation of 2-substituted allylic amides gives access to chiral oxazolines bearing a chloromethyl moiety for further synthetic manipulation. The [...] Read more.
The intramolecular halocyclization of alkenes possessing an internal heteroatom nucleophile leads to multifunctional heterocycles which are useful versatile intermediates in organic synthesis. The asymmetric chlorocyclisation of 2-substituted allylic amides gives access to chiral oxazolines bearing a chloromethyl moiety for further synthetic manipulation. The literature reports on this transformation involve complex syntheses of the 2-substituted allylic amides and cryogenic temperatures for achieving high enantioselectivities in the organocatalyzed halocyclization step. Based on the Heck reaction of aryl bromides and Boc-protected allylamine or allylamine benzamides, we developed a practical synthesis of 2-substituted allylic amides that does not require chromatography and accomplished their asymmetric halocyclization reaction with 24–92%ee under practical conditions (5 °C, CpME) catalyzed by (S)-(+)-DTBM-SEGPHOS. In addition, using appropriately substituted substrates, we generated Hammett plots and formulated a consistent mechanism for the halocyclization reaction which involves two competing modes of formation of the haliranium intermediate whose relative kinetics are governed by the electronic properties of the substrate. Full article
(This article belongs to the Special Issue Novel Approaches for Asymmetric Synthesis)
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19 pages, 7654 KiB  
Article
Rh(III)-Catalyzed Annulation of Boc-Protected Benzamides with Diazo Compounds: Approach to Isocoumarins
by Guangyu Dong, Chunpu Li and Hong Liu
Molecules 2019, 24(5), 937; https://doi.org/10.3390/molecules24050937 - 7 Mar 2019
Cited by 14 | Viewed by 4335
Abstract
A mild rhodium-catalyzed annulation of Boc-protected benzamides with diazo compounds via C−C/C−O bond formation has been explored. In the presence of [Cp*RhCl2]2, AgSbF6 and Cs2CO3, Boc-protected benzamides can be effectively annulated to yield isocoumarins in 0.5–2 h. Full article
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