David Chai

Tandem Pd-Catalyzed Double C-C Bond Formation : Effect of Water

A highly efficient water-accelerated palladium-catalyzed reaction of gem-dibromoolefins with a boronic acid via a tandem Suzuki-Miyaura coupling and direct arylation is reported. A wide range of aryl, alkenyl, and alkyl boronic acids, as well as a variety of substitution patterns on the phenyl ring, are tolerated. Additionally, mechanistic studies were conducted to ascertain the order of the couplings as well as the role(s) of water. Results from this study indicate that the major pathway is a Suzuki-Miyaura coupling/direct arylation sequence and that water accelerates the Pd(0) formation and Suzuki-Miyaura coupling.

Mechanistic Studies of Pd‐Catalyzed Regioselective Aryl CH Bond Functionalization with Strained Alkenes: Origin of Regioselectivity

Mechanistic studies of a palladium-catalyzed regioselective aryl C-H functionalization of 2-pyrrole phenyl iodide with norbornene are presented. Kinetic and spectroscopic analyses together with crystallographic data provide evidence for intermediates in a proposed stepwise mechanism. On the basis of the mechanistic studies, the origin of the regioselectivity is due to a ligand exchange between I(-) and HO(-) on the norbornyl palladium complex. These mechanistic studies also implicate that either alkoxide or water is responsible for the formation of the palladacycle, but a reversible ring-opening-ring-closing process of the palladacycle with HX can retard the rate of reaction of a key intermediate. The significant aspects of the proposed mechanism are discussed in detail.

Modular and stereoselective synthesis of tetrasubstituted helical alkenes via a palladium-catalyzed domino reaction.

A highly modular and stereoselective synthesis of tetrasubstituted helical alkenes is accomplished by a Pd-catalyzed norbornene-mediated domino reaction. This protocol features the rapid assembly of four C-C bonds via sequential C-H activations and carbopalladations along with efficient access to enantiopure bromoalkyl aryl alkyne precursors using homologative alkynylation as the key transformation. Three distinct elements of stereoselectivity were observed in the preparation of the chiral helical alkenes: retention of stereochemistry of the substrates, induced helical diastereoselectivity in the alkene formation, and the exclusive exo-facial selectivity of the norbornene incorporation.

Synthesis of 2-Oxazolones and α-Aminoketones via Palladium-Catalyzed Reaction of β,β-Dibromoenamides

β,β-Dibromoenamides show two different interesting reactivities based on the choice of R group under the reaction conditions. On the basis of mechanistic studies, both reactions proceed via an intermolecular Suzuki-Miyaura C-C coupling and an intramolecular C-O coupling.

Meontological Generativity: A Daoist Reading of the Thing

When it comes to the entity known as the Thing (das Ding), two philosophical interpretations are available: the ontological by Martin Heidegger and the ethical by Jacques Lacan. This essay offers a third in the guise of Daoist meontology. As Daoist cosmogony unfolds by way of nothingness (wu 無) and Dao acting in conjunction, the Thing cannot exist at that primal level of creation; it arises in the undifferentiated wholeness of the One. By locating the Thing as such, Daoism bestows upon it the mysteriousness of Dao, ensuring that it remains unspoiled by human endeavors and is a feat neither Heidegger nor Lacan can claim. The Thing thus protects Daoism against claims of nihilism, for each thing returns to its ancestral Thing, not to the nothingness that Dao employs to mold them.