The Elusive Seven-Membered Cyclic Imino Ether Tetrahydrooxazepine
Bart Verbraeken1, Jan Hullaert2, Joachim van Guyse1
1Supramolecular Chemistry group, Centre of Macromolecular Chemistry (CMaC), Department of Organic and Macromolecular Chemistry , Ghent University , Krijgslaan 281 S4 , 9000 Ghent , Belgium.
Abstract:
Cyclic imino ether heterocycles are used as ligands in transition metal catalysis, in various drugs and as reactive monomers in living cationic ring-opening polymerization (CROP). While five- and six-membered cyclic imino ethers, i.e. 2-oxazolines and 4,5-dihydro-1,3-oxazines, have extensively been studied in these areas, their seven-membered ring counterparts have remained unexplored. Herein, we report the synthesis of 2-phenyl-4,5,6,7-tetrahydro-1,3-oxazepine allowing reassignment of the earlier, incorrectly reported 4,5,6,7-tetrahydro-1,3-oxazepines as their N-acylated pyrrolidine isomers. Finally, we also report a comparison of the CROP reactivity of a homologous series of cyclic imino ethers with a 2-carbon, 3-carbon, and 4-carbon methylene bridge, revealing a remarkable ring size effect.
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