Arylsulfonyl Groups: The Best Cyclization Auxiliaries for the Preparation of ATRC γ‐Lactams can be Acidolytically Removed

Abstract

AbstractThe 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‐α‐polychloroamides, can be effectively removed from the target γ‐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.