Reaction progress kinetic analysis to obtain a comprehensive picture of complex catalytic reaction behavior is described. This methodology employs in situ measurements and simple manipulations to construct a series of graphical rate equations that enable analysis of the reaction to be accomplished from a minimal number of experiments. Such an analysis helps to describe the driving forces of a reaction and may be used to help distinguish between different proposed mechanistic models. This Review describes the procedure for undertaking such analysis for any new reaction under study.

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Direct methods for the trifluoromethylation of heteroaromatic systems are in extremely high demand in nearly every sector of chemical industry. Here we report the discovery of a general procedure using a benchtop stable trifluoromethyl radical source that functions broadly on a variety of electron deficient and rich heteroaromatic systems and demonstrates high functional group tolerance. This C-H trifluoromethylation protocol is operationally simple (avoids gaseous CF 3 I), scalable, proceeds at ambient temperature, can be used directly on unprotected molecules, and is demonstrated to proceed at the innately reactive positions of the substrate. The unique and orthogonal reactivity of the trifluoromethyl radical relative to aryl radicals has also been investigated on both a complex natural product and a pharmaceutical agent. Finally, preliminary data suggest that the regioselectivity of C-H trifluoromethylation can be fine-tuned simply by judicious solvent choice.medicinal chemistry | C-H functionalization | synthetic methodology T he trifluoromethyl group is becoming an increasingly common trait among molecules found in billion-dollar pharmaceuticals, agrochemicals, liquid crystals, dyes, and polymers (1-6). The inclusion of this motif and the unique properties its presence elicits is a testament to the success of chemical synthesis, as it is notably absent in Nature. Methodologies for the trifluoromethylation of arenes can be divided into two general categories (Fig. 1A): those that functionalize the inherently reactive positions of the substrate ("innate trifluoromethylation") and those that utilize substrate prefunctionalization or a directing group ("programmed trifluoromethylation"). For most applications, "programmed" aryl trifluoromethylation holds a distinct advantage because it can selectively functionalize positions that are not naturally reactive. Indeed, incredibly powerful methods have recently emerged in this arena (10-18). On the other hand, methods that capitalize on innate reactivity avoid the complication of preparing prefunctionalized substrates. We became interested in exploring "innate" aryl trifluoromethylation during our recent studies in the area of direct C-H arylation of heterocycles (19) and quinones (20) using radicals derived from boronic acid precursors. Aromatic heterocycles containing the trifluoromethyl group represent an important subsection of molecules of practical interest, particularly for pharmaceuticals, and therefore previously undescribed methods for their rapid assembly are in high demand. Our goal was to identify a reagent that would circumvent the use of gaseous CF 3 I (21), a reagent that is often avoided in pharmaceutical settings. At the start of our work, the task of replacing this reagent for the innate trifluormethylation of nitrogen containing heterocycles remained an unmet challenge.As briefly illustrated in Fig. 1, we evaluated numerous reagents for the trifluoromethylation of 4-t-butylpyridine as a model compound, with the aim of exploring those that might p...

The mechanism of the hydrolytic kinetic resolution (HKR) of terminal epoxides was investigated by kinetic analysis using reaction calorimetry. The chiral (salen)Co-X complex (X = OAc, OTs, Cl) undergoes irreversible conversion to (salen)Co-OH during the course of the HKR and thus serves as both precatalyst and cocatalyst in a cooperative bimetallic catalytic mechanism. This insight led to the identification of more active catalysts for the HKR of synthetically useful terminal epoxides.

The use of modern kinetic tools to obtain virtually continuous reaction progress data over the course of a catalytic reaction opens up a vista that provides mechanistic insights into both simple and complex catalytic networks. Reaction profiles offer a rate/concentration scan that tells the story of a batch reaction time course in a qualitative "fingerprinting" manner as well as in quantitative detail. Reaction progress experiments may be mathematically designed to elucidate catalytic rate laws from only a fraction of the number of experiments required in classical kinetic measurements. The information gained from kinetic profiles provides clues to direct further mechanistic analysis by other approaches. Examples from a variety of catalytic reactions spanning two decades of the author's work help to delineate nuances on a central mechanistic theme.

Molecular scaffolds containing alkylfluorine substituents are desired in many areas of chemical research from materials to pharmaceuticals. Herein, we report the invention of a new reagent (Zn(SO2CF2H)2, DFMS) for the innate difluoromethylation of organic substrates via a radical process. This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols. Regiochemical comparisons suggest that the CF2H radical generated from the new reagent possesses nucleophilic character.

Ever since Pasteur noticed that tartrate crystals exist in two non-superimposable forms that are mirror images of one another--as are left and right hands--the phenomenon of chirality has intrigued scientists. On the molecular level, chirality often has a profound impact on recognition and interaction events and is thus important to biochemistry and pharmacology. In chemical synthesis, much effort has been directed towards developing asymmetric synthesis strategies that yield product molecules with a significant excess of either the left-handed or right-handed enantiomer. This is usually achieved by making use of chiral auxiliaries or catalysts that influence the course of a reaction, with the enantiomeric excess (ee) of the product linearly related to the ee of the auxiliary or catalyst used. In recent years, however, an increasing number of asymmetric reactions have been documented where this relationship is nonlinear, an effect that can lead to asymmetric amplification. Theoretical models have long suggested that autocatalytic processes can result in kinetically controlled asymmetric amplification, a prediction that has now been verified experimentally and rationalized mechanistically for an autocatalytic alkylation reaction. Here we show an alternative mechanism that gives rise to asymmetric amplification based on the equilibrium solid-liquid phase behaviour of amino acids in solution. This amplification mechanism is robust and can operate in aqueous systems, making it an appealing proposition for explaining one of the most tantalizing examples of asymmetric amplification-the development of high enantiomeric excess in biomolecules from a presumably racemic prebiotic world.

The inexorable evolution of solid-phase single chirality is demonstrated for the first time for a proteinogenic amino acid. Enantioenrichment is observed both under attrition-enhanced conditions and without the aid of particle grinding. Differences in the form of the conversion profiles for the process under the two sets of conditions provide suggestions concerning the mechanism of the transformation.