期刊
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
卷 2014, 期 30, 页码 6734-6745出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201402769
关键词
Protecting groups; Deprotection; Lactams; Radicals; Cyclization; Amides
The N-arylsulfonyl group, which is the best and most useful cyclization auxiliary for the transition-metal-catalyzed atom transfer radical cyclization (ATRC) of N-allyl--polychloroamides, can be effectively removed from the target -lactams by using H2SO4-HOAc, without impairing the halogen functions. The reaction involves H+ attack on the aromatic moiety, and is strongly responsive to the electronic properties of the substituent bound to the aromatic ring: electron-donating groups, such as methyl or methoxy are, in fact, required for efficient deprotection. The N-p-nitrophenylsulfonyl cyclization auxiliary, in contrast to all the other sulfonyl groups tested, proved to be unsuitable for the ATRC, owing to a side reductive transposition that halts the redox cycle.
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