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Enantioselective [2+2] Photocycloaddition Reactions of Enones and Olefins with Visible Light Mediated by N , N ′‐Dioxide–Metal Complexes
Author(s) -
Yu Han,
Dong Shunxi,
Yao Qian,
Chen Long,
Zhang Dong,
Liu Xiaohua,
Feng Xiaoming
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804600
Subject(s) - enantioselective synthesis , chemistry , photochemistry , excited state , cycloaddition , bathochromic shift , intersystem crossing , metal , catalysis , terbium , fluorescence , organic chemistry , physics , quantum mechanics , nuclear physics , singlet state , ion
A 2‐alkenoylpyridine‐bound N , N ′‐dioxide–Tb III complex has been found to absorb visible light to reach the excited state, leading to the direct visible‐light‐excited catalytic enantioselective [2+2] cycloaddition of 2‐alkenoylpyridines to various alkenes in the absence of an additional photosensitizer. Diverse enantioenriched cyclobutanes were successfully obtained (yields up to 70 %, >19:1 d.r., 92 % ee ). The new chiral terbium(III) complex features a bathochromic shift, lower excitation energy, and facile intersystem crossing due to paramagnetic and heavy‐atom effects, which enable the antenna 2‐alkenoylpyridines to be excited. For comparison, a chiral N , N′ ‐dioxide–Sc III complex in combination with [Ru(bpy) 3 ]Cl 2 was efficient in the enantioselective photocycloaddition reactions of 2′‐hydroxychalcones with alkenes, thereby revealing that both substrates and metal salts have significant effects on the reaction.