Ring Contraction of Saturated Cyclic Amines and Rearrangement of Acyclic Amines Through Their Corresponding Hydroxylamines

Compared to modifications at the molecular periphery, skeletal adjustments present greater challenges. Within this context, skeletal rearrangement technology stands out for its significant advantages in rapidly achieving structural diversity. Yet, the development of this technology for ring contraction of saturated cyclic amines remains exceedingly rare. While most existing methods rely on specific substitution patterns to achieve ring contraction, there is a persistent demand for a more general strategy for substitution-free cyclic amines. To address this issue, we report a B(C6F5)3-catalyzed skeletal rearrangement of hydroxylamines with hydrosilanes. This methodology, when combined with the N-hydroxylation of amines, enables the regioselective ring contraction of cyclic amines and proves equally effective for rapid reorganization of acyclic amine skeletons. By this, the direct scaffold hopping of drug molecules and the strategic deletion of carbon atoms are achieved in a mild manner. Based on mechanistic experiments and density functional theory calculations, a possible mechanism for this process is proposed.

Oxoammonium salt-promoted diverse functionalization of saturated cyclic amines with dinucleophiles

Oxoammonium salt-promoted diverse functionalization of saturated cyclic amines with different dinucleophiles under mild conditions is presented. Specifically, when thiocyanate is used as a 1,3-dinucleophile, hexahydrothiazolo[4,5-b]pyridin-2(3H)-one derivatives are formed via the formation of the β-TEMPO-tethered cyclic iminium ion as a key intermediate. By contrast, when benzene-1,2-diamine is used as a 1,4-dinucleophile, 2-alkylquinoxaline derivatives are afforded via generation of the β-oxo cyclic iminium ion as a key intermediate. In addition, the usefulness of 2-alkylquinoxalines is showcased through their facile conversion into N-(2-oxo-2-(quinoxalin-2-yl)ethyl)nitrous amides featuring the synthetically useful N-NO moiety and the carbonyl group.

Electrophotochemical Ring-Opening Bromination of tert-Cycloalkanols

An electrophotochemical ring-opening bromination of unstrained tert-cycloalkanols has been developed. This electrophotochemical method enables the oxidative transformation of cycloalkanols with 5- to 7-membered rings into synthetically useful ω-bromoketones without the use of chemical oxidants or transition-metal catalysts. Alkoxy radical species would be key intermediates in the present transformation, which generate through homolysis of the O-Br bond in hypobromite intermediates under visible light irradiation.

Recent advances in the functionalization of saturated cyclic amines

Functionalized cyclic amines are the essential structural moieties of numerous biologically active compounds. This review summarized the most recent advances in the C–H, C–N and C–C bond functionalization of saturated cyclic amines.