Intramolecular iron(II)-catalyzed aminobromination of allyl N-tosyloxycarbamates

Electrochemical Bromination of Glycals

Herein, the convenient one-step electrochemical bromination of glycals using Bu₄NBr as the brominating source under metal-catalyst-free and oxidant-free reaction conditions was described. A series of 2-bromoglycals bearing different electron-withdrawing or electron-donating protective groups were successfully synthesized in moderate to excellent yields. The coupling of tri-O-benzyl-2-bromogalactal with phenylacetylene, potassium phenyltrifluoroborate, or a 6-OH acceptor was achieved to afford 2C-branched carbohydrates and disaccharides via Sonogashira coupling, Suzuki coupling, and Ferrier rearrangement reactions with high efficiency. The radical trapping and cyclic voltammetry experiments indicated that bromine radicals may be involved in the reaction process.

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

A library of pinane-based 2-amino-1,3-diols was synthesised in a stereoselective manner. Isopinocarveol prepared from (−)-α-pinene was converted into condensed oxazolidin-2-one in two steps by carbamate formation followed by a stereoselective aminohydroxylation process. The relative stereochemistry of the pinane-fused oxazolidin-2-one was determined by 2D NMR and X-ray spectroscopic techniques. The regioisomeric spiro-oxazolidin-2-one was prepared in a similar way starting from the commercially available (1R)-(−)-myrtenol (10). The reduction or alkaline hydrolysis of the oxazolidines, followed by reductive alkylation resulted in primary and secondary 2-amino-1,3-diols, which underwent a regioselective ring closure with formaldehyde or benzaldehyde delivering pinane-condensed oxazolidines. During the preparation of 2-phenyliminooxazolidine, an interesting ring–ring tautomerism was observed in CDCl₃.

Copper Promoted Regio- and Stereoselective Aminochlorination of Alkynes and Alkenes with NFSI

A simple and rapid copper-promoted aminochlorination of unactivated alkynes and alkenes with N-fluorobenzenesulfonimide (NFSI) was developed. Two series of chloroenamines and chloroamines were obtained in good to high yields. The chlorinated enamines could be obtained in a single E configuration. This reaction involved a radical process and the CuCl₂ acted as the Cl source and NFSI as the N source.

Visible-Light Promoted Distereodivergent Intramolecular Oxyamidation of Alkenes

The visible-light-promoted diastereodivergent intramolecular oxyamination of alkenes is described to construct oxazolindinones, pyrrolidinones and imidazolidones via mild generation of primary amidyl radicals from functionalized hydroxylamines. A unique phenomenon of highly diastereoselective ring-opening of aziridines controlled by electron sacrifices was observed. Highly diastereoselective amino alcohols derivatives were obtained efficiently through this protocol in gram scales. The mechanistic studies suggested the isolatable anti-aziridine intermediates were generated quickly from primary amidyl radicals and the diastereoselectivities were controlled by pK_a values of the electron sacrifices.

Iron-Catalyzed Diastereoselective Intramolecular Olefin Aminobromination with Bromide Ion

A new iron-catalyzed diastereoselective aminobromination method is reported for both internal and terminal olefins (yield up to 90% and dr up to >20:1). In this transformation, a functionalized hydroxylamine and bromide ion were used as the nitrogen and bromine source, respectively. This method is compatible with a broad range of olefins and provides a convenient approach to synthetically valuable vicinal bromo primary amines. Our studies suggest that both the diastereoselectivity and enantioselectivity for the olefin aminobromination can be controlled by iron catalysts.

Enzymatic C(sp3)-H Amination: P450-Catalyzed Conversion of Carbonazidates into Oxazolidinones

Cytochrome P450 enzymes can effectively promote the activation and cyclization of carbonazidate substrates to yield oxazolidinones via an intramolecular nitrene C-H insertion reaction. Investigation of the substrate scope shows that while benzylic/allylic C-H bonds are most readily aminated by these biocatalysts, stronger, secondary C-H bonds are also accessible to functionalization. Leveraging this "non-native" reactivity and assisted by fingerprint-based predictions, improved active-site variants of the bacterial P450 CYP102A1 could be identified to mediate the aminofunctionalization of two terpene natural products with high regio- and stereoselectivity. Mechanistic studies and KIE experiments show that the C-H activation step in these reactions is rate-limiting and proceeds in a stepwise manner, namely, via hydrogen atom abstraction followed by radical recombination. This study expands the reactivity scope of P450-based catalysts in the context of nitrene transfer transformations and provides first-time insights into the mechanism of P450-catalyzed C-H amination reactions.

Visible-light-promoted chloramination of olefins with N-chlorosulfonamide as both nitrogen and chlorine sources

A visible-light-promoted chloramination of olefins is reported.

Endeavors to access molecular complexity: strategic use of free radicals in natural product synthesis

Free radicals, which in the past were considered unruly chemical species, have become manageable and indispensable for synthetic organic chemistry. The unique nature of free radicals has allowed practitioners in organic synthesis to design flexible approaches to produce various materials ranging from small molecules to polymers. The present Personal Account describes the author's endeavors to create molecular complexity by the strategic use of free radicals, with an emphasis on the synthesis of bioactive natural products.

Formal synthesis of (-)-agelastatin A: an iron(II)-mediated cyclization strategy

An iron(II)-mediated aminohalogenation of a cyclopentenyl N-tosyloxycarbamate provided new access to the key intermediate for the synthesis of (-)-agelastatin A (AA, 1), a potent antiproliferative alkaloid. The present synthetic endeavour offered an insight into the mechanism underlying the iron(II)-mediated aminohalogenation of N-tosyloxycarbamate, in which the radical properties of the N-iron intermediates in the redox states were operative.