Transition metal-catalyzed C-C bond activation of four-membered cyclic ketones.

With the advent of new synthetic methodologies, carbon-carbon bond (C-C) activation strategies have uncovered not only new fundamental reactivity but also the potential for use as a highly efficient synthetic protocol. This chapter specifically discusses the use of four-membered ketone-based starting materials for C-C activation initiated transformations using a variety of transition metals. The two major modes of activation, oxidative addition and ß-C elimination, are presented as each pathway shows different mechanistic details and the ability to effect several types of reactions. Applications to the synthesis of complex molecules are presented and perspectives on future applications are considered.

The roles of counterion and water in a stereoselective cysteine-catalyzed Rauhut-Currier reaction: a challenge for computational chemistry.

The stereoselective Rauhut-Currier (RC) reaction catalyzed by a cysteine derivative has been explored computationally with density functional theory (M06-2X). Both methanethiol and a chiral cysteine derivative were studied as nucleophiles. The complete reaction pathway involves rate-determining elimination of the thiol catalyst from the Michael addition product. The stereoselective Rauhut-Currier reaction, catalyzed by a cysteine derivative as a nucleophile, has also been studied in detail. This reaction was experimentally found to be extremely sensitive to the reaction conditions, such as the number of water equivalents and the effect of potassium counterion. The E1cB process for catalyst elimination has been explored computationally for the eight possible stereoisomers. The effect of explicit water solvation and the presence of counterion (either K(+) or Na(+) ) has been studied for the lowest energy enantiomer pair (1S, 2R, 3S)/(1R, 2S, 3R).

Development of a cysteine-catalyzed enantioselective Rauhut-Currier reaction.

Herein, we report a full account of the development of an enantioselective Rauhut-Currier process that affords products in high yields and enantioselectivities using a cysteine-based catalyst. While traditional Morita-Baylis-Hillman catalysts were found to be essentially ineffective, various derivatives of protected cysteine were found to exhibit extraordinary reactivity and enantiotopic control. Extensive screening of reaction conditions led us to discover the enhanced effects of water as an additive and the chelating power of potassium in achieving higher enantiomer ratios. Mechanistic experiments also provided insight on the potential mechanism of the reaction in addition to possible transition states that provide the absolute stereochemistry formed in the observed products. Also included is a brief survey of the reaction scope involving different ring sizes as well as functionalized substrates.

Discovery of Tyrosine Kinase 2 (TYK2) Inhibitor (PF-06826647) for the Treatment of Autoimmune Diseases.

Tyrosine kinase 2 (TYK2) is a member of the JAK kinase family that regulates signal transduction downstream of receptors for the IL-23/IL-12 pathways and type I interferon family, where it pairs with JAK2 or JAK1, respectively. On the basis of human genetic and emerging clinical data, a selective TYK2 inhibitor provides an opportunity to treat autoimmune diseases delivering a potentially differentiated clinical profile compared to currently approved JAK inhibitors. The discovery of an ATP-competitive pyrazolopyrazinyl series of TYK2 inhibitors was accomplished through computational and structurally enabled design starting from a known kinase hinge binding motif. With understanding of PK/PD relationships, a target profile balancing TYK2 potency and selectivity over off-target JAK2 was established. Lead optimization involved modulating potency, selectivity, and ADME properties which led to the identification of the clinical candidate PF-06826647 (22).

Rh-Catalyzed Decarbonylation of Conjugated Ynones via Carbon-Alkyne Bond Activation: Reaction Scope and Mechanistic Exploration via DFT Calculations.

In this full article, detailed development of a catalytic decarbonylation of conjugated monoynones to synthesize disubstituted alkynes is described. The reaction scope and limitation has been thoroughly investigated, and a broad range of functional groups including heterocycles were compatible under the catalytic conditions. Mechanistic exploration via DFT calculations has also been executed. Through the computational study, a proposed catalytic mechanism has been carefully evaluated. These efforts are expected to serve as an important exploratory study for developing catalytic alkyne-transfer reactions via carbon-alkyne bond activation.

Access to Highly Substituted 7-Azaindoles from 2-Fluoropyridines via 7-Azaindoline Intermediates.

A versatile synthesis of 7-azaindoles from substituted 2-fluoropyridines is described. C3-metalation and 1,4-addition to nitroolefins provide substituted 2-fluoro-3-(2-nitroethyl)pyridines. A facile oxidative Nef reaction/reductive amination/intramolecular SNAr sequence furnishes 7-azaindolines. Finally, optional regioselective electrophilic C5-substitution (e.g., bromination or nitration) and subsequent in situ oxidation delivers highly functionalized 7-azaindoles in high overall efficiency.

Direct activation of relatively unstrained carbon-carbon bonds in homogeneous systems.

New modes of chemical reactivity are of high value to synthetic organic chemistry. In this vein, carbon-carbon (C-C) activation is an emerging field that offers new possibilities for synthesizing valuable complex molecules. This review discusses the pioneering stoichiometric discoveries in this field up to the most recent synthetic applications that apply catalytic transformations. Specifically, the review focuses on C-C activation in relatively unstrained systems, including stoichiometric reactions, chelation-directed and chelation-free catalytic reactions. While the field of C-C activation of relatively unstrained systems is underdeveloped, we expect that this review will provide insight into new developments and pave the path for robust, practical applications.

Rh(I)-catalyzed decarbonylation of diynones via C-C activation: orthogonal synthesis of conjugated diynes.

Utilization of C-C bond activation as a unique mode of reactivity for constructing C-C bonds provides new strategies for preparing important organic molecules. Development of a Rh(I)-catalyzed C-C activation of diynones to synthesize symmetrical and unsymmetrical conjugated diynes through decarbonylation is reported. This C-C cleavage strategy takes advantage of the innate reactivity of conjugated ynones without relying on any ring strain or auxiliary directing group. This alkynation method also has orthogonal properties compared to typical cross-coupling reactions.

Quasi-Biomimetic Ring Contraction Catalyzed by a Cysteine-Based Nucleophile: Total Synthesis of Sch-642305, Some Analogs and their Putative anti-HIV Activities.

Cysteine plays a number of important functional and structural roles in Nature, often in the realm of catalysis. Herein, we present an example of a cysteine-catalyzed Rauhut-Currier reaction for a potentially biomimetic synthesis of Sch-642305 and related analogs. In this key step of the synthesis we discuss interesting new discoveries and the importance of substrate-catalyst recognition, as well as cysteine's structural features. Also, we investigate the activity of Sch-642305 and four analogs in HIV-infected T-cells.