Palladium Catalyzed C–H Functionalization of <i>O</i>-Arylcarbamates: Selective <i>ortho</i>-Bromination Using NBS

A series of cyclometalated palladium complexes derived from O-phenylcarbamates has been synthesized by the reaction of the respective carbamates with Pd­(OAc)2 in the presence of acids, CF3CO2H, CF3SO3H, and p-TsOH. The palladacycles were observed to coordinate amines and electron rich anilines but not sulfonamides or carboxamides. Analysis of the tBu-NH2 adduct of the palladacycle 2b (2b·tBu-NH2) by NMR spectroscopy (NOE) revealed a cis-coordination of the amine. However, the amine adducts failed to undergo ortho-amination (C–N bond formation) under varied reaction conditions. Notably, the palladacycle 1d was found to react efficiently with N-iodosuccinimide (NIS) to yield the ortho-iodinated carbamate, 1e. More significantly, this reaction can be extended to a palladium-catalyzed ortho C–H bromination of aryl-O-carbamates even at 5 mol % loading of Pd­(OAc)2 using N-bromosuccinimide (NBS)

Imidazole Substituent Effects on Oxidative Reactivity of Tripodal(imid)₂(thioether)Cu^I Complexes

In the search for new bis(imidazole)thioether (BIT) copper complexes that accurately mimic the electronic and reactivity features of the CuM site of copper hydroxylase enzymes, a set of tripodal BIT ligands 4a,b−6a,b has been synthesized that vary according to the imidazole C-(Ph or H) and N-(H or Me) substituents, as well as the position (2- or 4-) of the tripodal attachment. Corresponding [(BIT)Cu(L)](PF6) complexes 7a,b′, 8a,b′, and 9a′,b′ [L = CO (a), CH3CN (b)] have been prepared and characterized spectroscopically. The IR spectra of 7a−9a (L = CO), specifically ν(CO), show little variation (2090–2100 cm−1), suggesting a similar electronic character of the Cu centers. In contrast, cyclic voltammetric analysis of these compounds (L = CH3CN) reveals quasi-reversible oxidation waves with significant variation of Epa in the range of + 0.45–0.57 V vs Fc/Fc+, depending on the imidazole substituents. Each of the [(BIT)Cu(CH3CN)]PF6 complexes reacts with dioxygen to form [(BIT)CuII2(μ-OH)2](PF6)2 derivatives, 10−12, but they vary considerably in their relative reactivity, following the same trend as the ease of their electrochemical oxidation, that is, [(2-BITNMe)Cu(CH3CN)]+ (9b′) > [(4-BITPh,NMe)Cu(CH3CN)]+ (8b′) > [(2-BITPh2,NMe)Cu(CH3CN)]+ (1a′) > [(4-BITPh,NH)Cu(CH3CN)]+ (7b′). Thus, N-Me substitution and 4-tethering on the imidazole unit increase oxidation and oxygenation reactivity, while Ph-substitution and 2-tethering decrease reactivity. PM3 and DFT calculations are employed to analyze the relative stability, the electronic features, the Cu−CO vibrtional frequency, and the electrochemical and oxidative reactivity of the complexes

Iodine-Catalyzed Aminosulfonation of Hydrocarbons by Imidoiodinanes. a Synthetic and Mechanistic Investigation

The amino-functionalization of a range of benzylic and some aliphatic saturated and unsaturated hydrocarbons by reaction with imido-iodinanes (PhINSO2Ar) is catalyzed by I2 under operationally simple and mild conditions. The first examples of 1,2-functionalization of unactivated C−H bonds using imido-iodinanes as aminating agents are reported. Mechanistic investigations, including Hammett analysis, kinetic isotope effects, a cyclopropane clock experiment, and stereoselectivity tests, are indicative of a stepwise pathway in C−N bond formation. Investigation into the nature of the active aminating species has led to the isolation of a novel aminating agent formulated as (ArSO2N)xIy (x = 1, y = 2; or x = 3, y = 4)

Synthesis of Cyclic Oligomers from Histidine-Derived Building Blocks Using Dynamic Combinatorial Chemistry

Histidine-derived hydrazide acetal monomers (3-dimethoxymethylbenzoyl)-l-histidine methyl ester 1 and (3-dimethoxymethylbenzoyl)-τ-benzyl-l-histidine methyl ester 2 were prepared from a histidine methyl ester and a τ-benzyl-histidine methyl ester by N-acylation with 3-(dimethoxymethyl)benzoic acid (3) followed by hydrazinolysis. Acid-promoted hydrolysis of each acetal hydrazide initially produced a library of cyclic oligomers that eventually converted to a cyclic dimer. The cyclic dimers 12 and 22 were spectroscopically characterized and found to direct their imidazole-bearing sidechains outward (exo). No evidence for templating the cyclic oligomers was observed using various metal ions and anionic substrates. The average of pKa1 and pKa2 of dimer 12 was determined by potentiometric titration to be 6.6. Dimer 12 was found to catalyze the hydrolysis of p-nitrophenylacetate 10 times faster than 4-methyl imidazole

Efficient Copper-Catalyzed Benzylic Amidation with Anhydrous Chloramine-T

Benzylic hydrocarbons are selectively converted to the corresponding sulfonamides by the [Cu(CH3CN)4]PF6-catalyzed reaction with anhydrous TolSO2NNaCl (chloramine-T). Under the same conditions, representative ethers are also α-amidated; olefins produce allyl sulfonamides, aziridines, and/or β-chloro sulfonamides

Imidazole Substituent Effects on Oxidative Reactivity of Tripodal(imid)₂(thioether)Cu^I Complexes

In the search for new bis(imidazole)thioether (BIT) copper complexes that accurately mimic the electronic and reactivity features of the CuM site of copper hydroxylase enzymes, a set of tripodal BIT ligands 4a,b−6a,b has been synthesized that vary according to the imidazole C-(Ph or H) and N-(H or Me) substituents, as well as the position (2- or 4-) of the tripodal attachment. Corresponding [(BIT)Cu(L)](PF6) complexes 7a,b′, 8a,b′, and 9a′,b′ [L = CO (a), CH3CN (b)] have been prepared and characterized spectroscopically. The IR spectra of 7a−9a (L = CO), specifically ν(CO), show little variation (2090–2100 cm−1), suggesting a similar electronic character of the Cu centers. In contrast, cyclic voltammetric analysis of these compounds (L = CH3CN) reveals quasi-reversible oxidation waves with significant variation of Epa in the range of + 0.45–0.57 V vs Fc/Fc+, depending on the imidazole substituents. Each of the [(BIT)Cu(CH3CN)]PF6 complexes reacts with dioxygen to form [(BIT)CuII2(μ-OH)2](PF6)2 derivatives, 10−12, but they vary considerably in their relative reactivity, following the same trend as the ease of their electrochemical oxidation, that is, [(2-BITNMe)Cu(CH3CN)]+ (9b′) > [(4-BITPh,NMe)Cu(CH3CN)]+ (8b′) > [(2-BITPh2,NMe)Cu(CH3CN)]+ (1a′) > [(4-BITPh,NH)Cu(CH3CN)]+ (7b′). Thus, N-Me substitution and 4-tethering on the imidazole unit increase oxidation and oxygenation reactivity, while Ph-substitution and 2-tethering decrease reactivity. PM3 and DFT calculations are employed to analyze the relative stability, the electronic features, the Cu−CO vibrtional frequency, and the electrochemical and oxidative reactivity of the complexes

Copper-Catalyzed Amidation of 2-Phenylpyridine with Oxygen as the Terminal Oxidant

The Cu(OAc)2-catalyzed, O2-mediated amidation of 2-phenylpyridine via C−H bond activation is reported. A variety of nitrogen reagents including sulfonamides, carboxamides, and anilines participate in the reaction in moderate to good yields

Palladium-Catalyzed Carboxylation of Allyl Stannanes

Palladium-Catalyzed Carboxylation of Allyl Stannane

Imidazole Substituent Effects on Oxidative Reactivity of Tripodal(imid)₂(thioether)Cu^I Complexes

In the search for new bis(imidazole)thioether (BIT) copper complexes that accurately mimic the electronic and reactivity features of the CuM site of copper hydroxylase enzymes, a set of tripodal BIT ligands 4a,b−6a,b has been synthesized that vary according to the imidazole C-(Ph or H) and N-(H or Me) substituents, as well as the position (2- or 4-) of the tripodal attachment. Corresponding [(BIT)Cu(L)](PF6) complexes 7a,b′, 8a,b′, and 9a′,b′ [L = CO (a), CH3CN (b)] have been prepared and characterized spectroscopically. The IR spectra of 7a−9a (L = CO), specifically ν(CO), show little variation (2090–2100 cm−1), suggesting a similar electronic character of the Cu centers. In contrast, cyclic voltammetric analysis of these compounds (L = CH3CN) reveals quasi-reversible oxidation waves with significant variation of Epa in the range of + 0.45–0.57 V vs Fc/Fc+, depending on the imidazole substituents. Each of the [(BIT)Cu(CH3CN)]PF6 complexes reacts with dioxygen to form [(BIT)CuII2(μ-OH)2](PF6)2 derivatives, 10−12, but they vary considerably in their relative reactivity, following the same trend as the ease of their electrochemical oxidation, that is, [(2-BITNMe)Cu(CH3CN)]+ (9b′) > [(4-BITPh,NMe)Cu(CH3CN)]+ (8b′) > [(2-BITPh2,NMe)Cu(CH3CN)]+ (1a′) > [(4-BITPh,NH)Cu(CH3CN)]+ (7b′). Thus, N-Me substitution and 4-tethering on the imidazole unit increase oxidation and oxygenation reactivity, while Ph-substitution and 2-tethering decrease reactivity. PM3 and DFT calculations are employed to analyze the relative stability, the electronic features, the Cu−CO vibrtional frequency, and the electrochemical and oxidative reactivity of the complexes