Selective Electrochemical Oxidation of Functionalized Pyrrolidines.

A method for the selective electrochemical aminoxyl-mediated Shono-type oxidation of pyrrolidines to pyrrolidinones is described. These transformations show the high selectivity and functional group compatibility. This chemistry also demonstrates the use of an operationally simple ElectraSyn 2.0 and cost-effective stainless-steel electrode for the electrochemical oxidation of functionalized pyrrolidines.

Differentiation of Deprotonated Acyl-, N-, and O-Glucuronide Drug Metabolites by Using Tandem Mass Spectrometry Based on Gas-Phase Ion-Molecule Reactions Followed by Collision-Activated Dissociation.

Glucuronidation, a common phase II biotransformation reaction, is one of the major in vitro and in vivo metabolism pathways of xenobiotics. In this process, glucuronic acid is conjugated to a drug or a drug metabolite via a carboxylic acid, a hydroxy, or an amino group to form acyl-, O-, and/or N-glucuronide metabolites, respectively. This process is traditionally thought to be a detoxification pathway. However, some acyl-glucuronides react with biomolecules in vivo, which may result in immune-mediated idiosyncratic drug toxicity (IDT). In order to avoid this, one may attempt in early drug discovery to modify the lead compounds in such a manner that they then have a lower probability of forming reactive acyl-glucuronide metabolites. Because most drugs or drug candidates bear multiple functionalities, e.g., hydroxy, amino, and carboxylic acid groups, glucuronidation can occur at any of those. However, differentiation of isomeric acyl-, N-, and O-glucuronide derivatives of drugs is challenging. In this study, gas-phase ion-molecule reactions between deprotonated glucuronide metabolites and BF3 followed by collision-activated dissociation (CAD) in a linear quadrupole ion trap mass spectrometer were demonstrated to enable the differentiation of acyl-, N-, and O-glucuronides. Only deprotonated N-glucuronides and deprotonated, migrated acyl-glucuronides form the two diagnostic product ions: a BF3 adduct that has lost two HF molecules, [M - H + BF3 - 2HF]-, and an adduct formed with two BF3 molecules that has lost three HF molecules, [M - H + 2BF3 - 3HF]-. These product ions were not observed for deprotonated O-glucuronides and unmigrated, deprotonated acyl-glucuronides. Upon CAD of the [M - H + 2BF3 - 3HF]- product ion, a diagnostic fragment ion is formed via the loss of 2-fluoro-1,3,2-dioxaborale (MW of 88 Da) only in the case of deprotonated, migrated acyl-glucuronides. Therefore, this method can be used to unambiguously differentiate acyl-, N-, and O-glucuronides. Further, coupling this methodology with HPLC enables the differentiation of unmigrated 1-ß-acyl-glucuronides from the isomeric acyl-glucuronides formed upon acyl migration. Quantum chemical calculations at the M06-2X/6-311++G(d,p) level of theory were employed to probe the mechanisms of the reactions of interest.

Synthetic and mechanistic studies of Pd-catalyzed C-H arylation with diaryliodonium salts: evidence for a bimetallic high oxidation state Pd intermediate.

This contribution describes the substrate scope and mechanism of Pd-catalyzed ligand-directed C-H arylation with diaryliodonium salts. This transformation was applied to the synthesis of a variety of different biaryl products, using directing groups including pyridines, quinolines, pyrrolidinones, and oxazolidinones. Electronically and sterically diverse aryl groups (Ar) were transferred in high yield using iodine(III) reagents of general structure [Mes-I-Ar]BF(4). Mechanistic investigations have been conducted that establish the kinetic order of the catalytic reaction in each component, determine the resting state of the catalyst and the iodine(III) reagent, quantify the electronic influence of the arylating reagent on the reaction rate, and establish the intra- and intermolecular 1 degree H/D kinetic isotope effect. On the basis of these studies, this transformation is proposed to proceed via turnover-limiting oxidation of the Pd dimer [Pd(N~C)(OAc)](2) (N~C = 3-methyl-2-phenylpyridine) by [Mes-I-Ph]BF(4). This mechanism implicates a bimetallic high oxidation state Pd species as a key catalytic intermediate. The significance of this and other aspects of the proposed mechanism are discussed in detail.

Reactions of hypervalent iodine reagents with palladium: mechanisms and applications in organic synthesis.

The unique reactivity of hypervalent iodine reagents with Pd0 and PdII complexes has been exploited for a variety of synthetically useful organic transformations. For example, IIII reagents have been used in place of aryl halides for diverse Pd-catalyzed C-C and C-heteroatom bond-forming cross-coupling reactions. In addition, these reagents have found application in Pd-catalyzed oxidation reactions, including the oxidative functionalization of C-H bonds and the 1,2-aminooxygenation of olefinic substrates. This review discusses both the synthetic utility and the interesting mechanistic features of these transformations.

Room temperature palladium-catalyzed 2-arylation of indoles.

This communication describes the rational development of a PdII-catalyzed method for the direct 2-arylation of indoles using [Ar-IIII-Ar]BF4. These reactions proceed under remarkably mild conditions (often at room temperature and in the presence of ambient air and moisture), and these features are believed to be the result of a PdII/IV mechanism operating in these systems. These transformations can be used to prepare functionally diverse 2-arylated indoles and pyrroles, and their potential utility has been expanded by the development of an in situ procedure for generating the iodine(III) arylating reagents.

Oxidative C-H activation/C-C bond forming reactions: synthetic scope and mechanistic insights.

This paper describes a new palladium-catalyzed method for C-H activation/carbon-carbon bond formation with hypervalent iodine arylating agents. This transformation has been applied to a variety of arene and benzylic substrates containing different directing groups (pyridines, quinolines, oxazolidinones, and amides) and proceeds with high levels of regiocontrol. Mechanistic experiments provide preliminary evidence in support of an unusual mechanism for this transformation involving a Pd(II)/Pd(IV) catalytic cycle.