Selective transition-metal-free vicinal cis-dihydroxylation of saturated hydrocarbons

Iodonitrene: a direct metal-free electrophilic aminating reagent

Iodonitrene is a new type of reactive electrophilic aminating reagent that opens up opportunities for new discoveries.

Stereoselective Synthesis of Cyclobutanes by Contraction of Pyrrolidines

Here we report a contractive synthesis of multisubstituted cyclobutanes containing multiple stereocenters from readily accessible pyrrolidines using iodonitrene chemistry. Mediated by a nitrogen extrusion process, the stereospecific synthesis of cyclobutanes involves a radical pathway. Unprecedented unsymmetrical spirocyclobutanes were prepared successfully, and a concise, formal synthesis of the cytotoxic natural product piperarborenine B is reported.

Vicinal, Double C-H Functionalization of Alcohols via an Imidate Radical-Polar Crossover Cascade

A double functionalization of vicinal sp3 C-H bonds has been developed, wherein a β amine and γ iodide are incorporated onto an aliphatic alcohol in a single operation. This approach is enabled by an imidate radical chaperone, which selectively affords a transient β alkene that is amino-iodinated in situ. Overall, the radical-polar-crossover cascade entails the following key steps: (i) β C-H iodination via 1,5-hydrogen atom transfer (HAT), (ii) desaturation via I2 complexation, and (iii) vicinal amino-iodination of an in situ generated allyl imidate. The synthetic utility of this double C-H functionalization is illustrated by conversion of aliphatic alcohols to a diverse collection of α,β,γ substituted products bearing heteroatoms on three adjacent carbons. The radical-polar crossover mechanism is supported by various experimental probes, including isotopic labeling, intermediate validation, and kinetic studies.

Alkyliodines in High Oxidation State: Enhanced Synthetic Possibilities and Accelerated Catalyst Turn-Over

In contrast to aryliodine(III) compounds, which have matured into a particularly attractive class of oxidants in modern synthesis, the synthetic potential of related alkyliodine(III) derivatives has remained widely underestimated. This is surprising since several unique synthetic possibilities arise directly from the low stability of their central carbon-iodine bond. In this respect, these high-oxidation-state iodine compounds resemble environmentally benign variants of the prominent metal counterparts such as those derived from palladium, nickel and copper. This Concept article summarizes the general reactivity trends in alkyliodine(III) chemistry and discusses selected examples of their strategic use as highly reactive, transient species in organic synthesis and homogeneous catalysis.

Catalytic Transfer Hydrogenation Using Biomass as Hydrogen Source

We developed an operationally simple method for the direct use of biomass-derived chemical entities in a fundamentally important process, such as hydrogenation. Various carbohydrates, starch, and lignin were used for stereoselective hydrogenation. Employing a transition metal catalyst and a novel catalytic system, the reduction of alkynes, alkenes, and carbonyl groups with high yields was demonstrated. The regioselective hydrogenation to access different stereoisomers was established by simple variations in the reaction conditions. This work is based on an unprecedented catalytic system and represents a straightforward application of biomass as a reducing reagent in chemical reactions.

PIDA/I2-Mediated α- and β-C(sp3)-H Bond Dual Functionalization of Tertiary Amines

The α,β-C(sp³)-H bond dual functionalization of tertiary amines is still a challenging task for both organic and medicinal chemists. Herein a direct, mild, metal-free, and site-specific method mediated by PIDA/I₂ was developed for α,β-C(sp³)-H bond dual functionalization of tertiary amines, and this method can provide facile access to α-keto lactams or rarely studied α,α-diiodo lactams. Moreover, this method was used for the effective syntheses of three natural products [obscurumine C (13), obscurumine O (17), and strychnocarpine (18)] and direct preparation of mimics of the in vivo metabolites of two FDA-approved drugs (imatinib and donepezil) in 36-60% overall yield. The method represents a promising protocol for the late-stage α,β-C(sp³)-H bond oxidative dual functionalization of tertiary amine-containing drugs and complex natural products.

β C-H di-halogenation via iterative hydrogen atom transfer

A radical relay strategy for mono- and di-halogenation (iodination, bromination, and chlorination) of sp3 C-H bonds has been developed. This first example of β C-H di-halogenation is achieved through sequential C-H abstraction by iterative, hydrogen atom transfer (HAT). A double C-H functionalization is enabled by in situ generated imidate radicals, which facilitate selective N˙ to C˙ radical translocation and tunable C-X termination. The versatile, geminal di-iodide products are further elaborated to β ketones and vinyl iodides. Mechanistic experiments explain the unique di-functionalization selectivity of this iterative HAT pathway, wherein the second C-H iodination is twice as fast as the first.

Aerobic, Metal-Free, and Catalytic Dehydrogenative Coupling of Heterocycles: En Route to Hedgehog Signaling Pathway Inhibitors

The nitrosonium ion-catalyzed dehydrogenative coupling of heteroarenes under mild reaction conditions is reported. The developed method utilizes ambient molecular oxygen as a terminal oxidant, and only water is produced as byproduct. Dehydrogenative coupling of heteroarenes translated into the rapid discovery of novel hedgehog signaling pathway inhibitors, emphasizing the importance of the developed methodology.

A unified photoredox-catalysis strategy for C(sp3)-H hydroxylation and amidation using hypervalent iodine

We report a unified photoredox-catalysis strategy for both hydroxylation and amidation of tertiary and benzylic C-H bonds. Use of hydroxyl perfluorobenziodoxole (PFBl-OH) oxidant is critical for efficient tertiary C-H functionalization, likely due to the enhanced electrophilicity of the benziodoxole radical. Benzylic methylene C-H bonds can be hydroxylated or amidated using unmodified hydroxyl benziodoxole oxidant Bl-OH under similar conditions. An ionic mechanism involving nucleophilic trapping of a carbocation intermediate by H2O or CH3CN cosolvent is presented.

Visible light-promoted dihydroxylation of styrenes with water and dioxygen

An efficient visible light promoted metal-free dihydroxylation of styrenes with water and dioxygen has been developed for the construction of vicinal alcohols.