期刊
HELVETICA CHIMICA ACTA
卷 104, 期 9, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/hlca.202100080
关键词
halocyclization; halogen bonding; halogens; amine catalyst; reaction mechanisms; iodine complex
资金
- JSPS KAKENHI [JP20H04801, JP19H05630]
In halogen chemistry, the reaction between amines and N-halosuccinimides is complex, with NIS mainly forming non-covalent halogen bonded amine complexes and similar behavior observed for NBS, requiring catalysis with an appropriate Brønsted acid.
An arguable expectation in halogen chemistry is that an amine will react oxidatively with an N-halosuccinimide (NXS) to form an N-halogenated species bearing a covalent N-X bond. While likely for NCS under most conditions, we find this expectation simply not true for NIS and largely inaccurate for NBS. Herein, we disclose evidence through systematic NMR and X-ray studies that non-covalent halogen bonded amine complexes of NIS predominate over covalent N-halogenated species, even with primary and secondary amines. For example, during the catalytic electrophilic halocyclization of gem-disubstituted alkenes by cinchona-like amines, the quinuclidine complexes of NIS and NBS display lower reactivity than their parent N-halosuccinamides and require the presence of an appropriate Bronsted acid. Specifically, a Bronsted acid and quinuclidine jointly catalyze the halo-cycloetherification of gamma-alkenyl alcohols with NIS or NBS, while only quinuclidine acts as a catalyst in the halolactonization of gamma-alkenoic acids. Although our evidence confirms a transient N-halogenated quaternary ammonium salt as the halonium species, it is important to note that NIS predominantly forms 'off-cycle' halogen bonded amine complexes in solution.
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