Catalytic methods are important tools for the synthesis of C−C bonds under mild and ambient conditions. Palladium chemistry predominates in this area because it offers the opportunity to form several different types of bonds in one pot. Palladium can also tolerate a variety of functional groups. Among the many investigations of catalytic aryl−aryl couplings, the most successful technique has been the Suzuki reaction, which uses an arylboronic acid to attack an aryl−Pd bond. This Account reports our methodology, based on the cooperative action of Pd and norbornene, that achieves selective aryl−aryl coupling through C−halide and C−H activation. We are primarily interested in Pd-catalyzed sequential reactions. These reactions combine palladium as an inorganic catalyst and a strained olefin such as norbornene as an organic catalyst and can lead to biphenyl derivatives. While the palladium facilitates C−C bond formation through C−halide and C−H activation, the norbornene contributes to the construction of a pa...

Catalytic sequential reactions involving palladacycle-directed aryl coupling steps.

Organocopper reagents provide the most general synthetic tools in organic chemistry for nucleophilic delivery of hard carbanions to electrophilic carbon centers. A number of structural and mechanistic studies have been reported and have led to a wide variety of mechanistic proposals, some of which might even be contradictory to others. With the recent advent of physical and theoretical methodologies, the accumulated knowledge on organocopper chemistry is being put together into a few major mechanistic principles. This review will summarize first the general structural features of organocopper compounds and the previous mechanistic arguments, and then describe the most recent mechanistic pictures obtained through high-level quantum mechanical calculations for three typical organocuprate reactions, carbocupration, conjugate addition, and S(N)2 alkylation. The unified view on the nucleophilic reactivities of metal organocuprate clusters thus obtained has indicated that organocuprate chemistry represents an intricate example of molecular recognition and supramolecular chemistry, which chemists have long exploited without knowing it. Reasoning about the uniqueness of the copper atom among neighboring metal elements in the periodic table will be presented.

Wherefore Art Thou Copper? Structures and Reaction Mechanisms of Organocuprate Clusters in Organic Chemistry.

In the late 1990s Catellani reported a remarkable palladium-catalyzed domino reaction [1] in the presence of norbornene, in which aryl iodides were alkylated at the ortho positions by alkyl halides followed by a Mizoroki-Heck reaction to afford products of type 1 (Scheme 1) [2–4]. The process allowed for the construction of up to three carbon–carbon bonds in a single reaction using simple, commercially available starting materials. We called this process the Catellani reaction, and in the past decade considerable attention has been focused upon unlocking its synthetic potential. This review will primarily focus upon the mechanistic aspects of the Catellani reaction, followed by an overview of the synthetic scope of molecules currently accessible with this technology.

Synthesis in the key of Catellani: norbornene-mediated ortho C-H functionalization.

Interpretations of enzyme reaction stereospecificity

Regioselektive Synthese o,o′‐disubstituierter Vinylarene über einen komplexen Katalysecyclus

Earlier evidence led to the view that in bimolecular olefin-forming eliminations the anti steric course is generally preferred over the syn. Recent experiments, however, show that in some common bimolecular elimination reactions, notably those involving onium bases, syn- and anti-eliminations proceed side by side, the former preferentially leading to the trans- and the latter to the cis-olefins.

The syn and anti Steric Course in Bimolecular Olefin‐Forming Eliminations

Kinetic data were obtained for the dehydrohalogenation in C6H6 and PhMe of vic-dihaloalkanes and vic-dihalocycloalkanes in the presence of KOCMe3. The mechanism involved oligomeric alc. aggregates which affected the stereochem. of the reaction. [on SciFinder (R)]

Metallbindungsphänomene: Alkoholat‐Aggregate als unmittelbare Teilnehmer an Eliminierungsreaktionen

syn-Coplanar cleavage of hydrogen halide, esp. the syn -> trans process, was favored in the dehydrohalogenation of trans-1,2-dichlorocyclodecane and trans-1,2-dibromocyclodecane, and the anti elimination, which was most favored with acyclic compds., was retarded. The transition state for syn elimination was thought to be stabilized by redn. in transannular repulsive forces. The dehydrohalogenation rate depended only slightly on the solvent. [on SciFinder (R)]

Jiři Sicher

Papers

The syn and anti Steric Course in Bimolecular Olefin‐Forming Eliminations

Metallbindungsphänomene: Alkoholat‐Aggregate als unmittelbare Teilnehmer an Eliminierungsreaktionen

Preferred syn‐Elimination from trans‐1,2‐Dichloro‐ and trans‐1,2‐Dibromocyclodecane