Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue

Hypervalent iodine(V) reagents, such as Dess–Martin periodinane (DMP) and 2‐iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O₂) would immediately enable use of O₂ as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.     

Total Synthesis of (−)‐Spiroleucettadine

One of a number of intriguing new alkaloids isolated from the Leucetta sp. sponge in 2004, spiroleucettadine displayed unique structural features on a restricted scaffold: a trans ‐fused 5,5‐bicyclic ring system together with an amino hemiketal moiety. Attempts to synthesize the initially proposed structure failed, raising questions as to its veracity, and structure revision ensued in 2008; no successful synthetic approach has been reported to date. Herein, we describe the enantiospecific total synthesis of (−)‐spiroleucettadine by a highly efficient biomimetic approach starting from l ‐tyrosine. One of two key hypervalent‐iodine‐mediated oxidation reactions forged the spirocyclic center, and the other enabled the installation of the methylamine side chain in the penultimate step. Our approach provides synthetic access to a new class of spiroannulated natural products and will enable future studies of the structure–biological‐activity relationships of these antibacterial compounds.     

Base‐Promoted Coupling of Carbon Dioxide,Amines, and N‐Tosylhydrazones: A Novel and Versatile Approach to Carbamates

A base‐promoted three‐component coupling of carbon dioxide, amines, and N‐tosylhydrazones has been developed. The reaction is suggested to proceed via a carbocation intermediate and constitutes an efficient and versatile approach for the synthesis of a wide range of organic carbamates. The advantages of this method include the use of readily available substrates, excellent functional group tolerance, wide substrate scope, and a facile work‐up procedure.     

Modular Synthesis of Multisubstituted Furans through Palladium‐Catalyzed Three‐Component Condensation of Alkynylbenziodoxoles,Carboxylic Acids,and Imines

Mild and regiocontrolled synthesis of a multisubstituted furan is achieved through Pd(OAc)₂‐catalyzed room‐temperature condensation of an alkynylbenziodoxole, a carboxylic acid, and an enolizable ketimine, which contribute to C1, CO, and C2 fragments, respectively, to the furan skeleton. The reaction tolerates a broad range of functional groups in each of the reaction components, and enables highly modular and flexible synthesis of variously substituted furans. The reaction is particularly effective for the rapid generation of tri‐ and tetraarylfurans and furan‐containing oligoarylenes without relying on conventional cross‐coupling chemistry.     

CO2 Conversion with Alcohols and Amines into Carbonates,Ureas, and Carbamates over CeO2 Catalyst in the Presence and Absence of 2‐Cyanopyridine

Recent progress on the CeO₂ catalyzed synthesis of organic carbonates, ureas, and carbamates from CO₂+alcohols, CO₂+amines, and CO₂+alcohols+amines, respectively, is reviewed. The reactions of CO₂ with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H₂O is essential in order to get the target product in high yield. One of the effective method of the H₂O removal from the related reaction systems is the combination with the hydration of 2‐cyanopyridine to 2‐picolinamide, which is also catalyzed by CeO₂.     

Synthesis of Polysubstituted Iodoarenes Enabled by Iterative Iodine‐Directed para and ortho C−H Functionalization

Among halogenated aromatics, iodoarenes are unique in their ability to produce the bench‐stable halogen(III) form. Earlier, such iodine(III) centers were shown to enable C?H functionalization ortho to iodine via halogen‐centered rearrangement. The broader implications of this phenomenon are explored by testing the extent of an unusual iodane‐directed para C?H benzylation, as well as by developing an efficient C?H coupling with sulfonyl‐substituted allylic silanes. Through the combination of the one‐shot nature of the coupling event and the iodine retention, multisubstituted arenes can be prepared by sequentially engaging up to three aromatic C?H sites. This type of iodine‐based iterative synthesis will serve as a tool for the formation of value‐added aromatic cores.     

Iron‐Catalyzed Mild and Selective Hydrogenative Cross‐Coupling of Nitriles and Amines To Form Secondary Aldimines

The first example of a base‐metal‐catalyzed homogeneous hydrogenative coupling of nitriles and amines to selectively form secondary cross‐imines is reported. The reaction is catalyzed under mild conditions by a well‐defined (iPr‐PNP)Fe(H)Br(CO) pincer pre‐catalyst and catalytic t BuOK.     

N‐Heterocyclic Carbene–Palladium Complexes as Efficient Catalysts for the Oxidative Carbonylation of Amines to Ureas

A highly efficient oxidative carbonylation reaction of amines to ureas was developed making use of carbene–palladium complexes in the absence of any promoter. Both aliphatic amines and aromatic amines were transformed in good to excellent yields to the expected ureas.     

A Novel Synthesis of N-Methyl-N-aryl Carbamates from Aromatic Amines and Dimethyl Carbonate Catalyzed by K2CO3／Bu4NBr

A facile synthesis of N-methyl-N-aryl carbamates from aromatic amines and dimethyl carbonate (DMC) has been achieved with high yields in the presence of potassium carbonate (K2CO3) and tetrabutylammonium bromide (Bu4NBr) under solvent-free conditions.     

Palladium‐Catalyzed N‐Alkylation of Amides and Amines with Alcohols Employing the Aerobic Relay Race Methodology

Possibly because homogeneous palladium catalysts are not typical borrowing hydrogen catalysts and ligands are thus ineffective in catalyst activation under conventional anaerobic conditions, they had not been used in the N‐alkylation reactions of amines/amides with alcohols in the past. By employing the aerobic relay race methodology with Pd‐catalyzed aerobic alcohol oxidation being a more effective protocol for alcohol activation, ligand‐free homogeneous palladiums are successfully used as active catalysts in the dehydrative N‐alkylation reactions, giving high yields and selectivities of the alkylated amides and amines. Mechanistic studies implied that the reaction most probably proceeds via the novel relay race mechanism we recently discovered and proposed.     

A General and Selective Rhodium‐Catalyzed Reduction of Amides,N‐Acyl Amino Esters,and Dipeptides Using Phenylsilane

This article describes a selective reduction of functionalized amides, including N‐acyl amino esters and dipeptides, to the corresponding amines using simple [Rh(acac)(cod)]. The catalyst shows excellent chemoselectivity in the presence of different sensitive functional moieties.     

Heterogeneous CuII‐Catalysed Solvent‐Controlled Selective N‐Arylation of Cyclic Amides and Amines with Bromo‐iodoarenes

A selective N‐arylation of cyclic amides and amines in DMF and water, respectively, catalysed by Cu^II/Al₂O₃ has been achieved. This protocol has been employed for the synthesis of a library of arenes bearing a cyclic amide and an amine moiety at two ends, including a few scaffolds of therapeutic importance. The mechanism has been established based on detailed electron paramagnetic resonance (EPR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), UV diffuse reflectance spectroscopy (DRS) and inductively coupled plasma‐mass spectrometry (ICP‐MS) studies of the catalyst at different stages of the reaction. The Cu^II/Al₂O₃ catalyst was recovered and recycled for subsequent reactions.