Access to Indene Derivatives by a Sequence of Intermolecularanti-Carbopalladation, Heck Reaction, and Electrophilic Attack

Pd(II)-Catalyzed Intramolecular Acetoxylative (3 + 2) Annulation of Propargylic Alcohol and Alkene: Polycyclic Oxa-heterocycle Synthesis and Mechanistic Insight

A Pd(II)-catalyzed intramolecular and highly selective acetxoylative (3 + 2) annulation of propargylic alcohol and alkene is reported. Mechanistically, a hydroxy-guided regioselective alkyne acetoxypalladation is followed by 6-exo-trig alkene insertion to form an alkyl-Pd(II) intermediate. After oxidation, the resulting cyclometalated alkoxy-Pd(IV)-alkyl undergoes direct reductive elimination to afford a polycyclic oxa-heterocycle. When an additional coordinating site or ligand accessible by palladium is present, an S_N2-type C-C reductive elimination of alkyl-Pd(IV) instead occurs along with hydroxy acetylation, affording 3-bicyclo[4.1.0]heptan-5-one products.

Intramolecular trans-Carbocarbonation of Internal Alkynes by a Cascade of Formal anti-Carbopalladation/Cyclopropanol Opening

An intramolecular cascade reaction consisting of a formal anti-carbopalladation terminated by the ring-opening of a cyclopropanol unit is presented. The products, which involve tetrasubstituted alkene units embedded in an oligocyclic ring system, are generated in moderate to excellent yield. The opening of the cyclopropanol unit leads to a keto group in the γ-position to the emerging double bond.

Intramolecular Pd-Catalyzed Formal anti-Carboalkoxylation of Alkynes: Access to Tetrasubstituted Enol Ethers

An intramolecular Pd-catalyzed formal anti-carboalkoxylation reaction is presented that provides access to tetrasubstituted enol ethers. The key to success is a cascade consisting of a formal anti-carbopalladation of a carbon-carbon triple bond followed by a nucleophilic attack of a hydroxy group at the emerging vinyl organopalladium species. The desired transformation proceeded smoothly with primary, secondary, and tertiary alcohols, and even with phenols. Depending on the substitution pattern of the enol ethers, a further Tsuji-Trost-type step may occur resulting in oligocyclic ketals.

trans-Carbocarbonation of Internal Alkynes through a Formal anti-Carbopalladation/C-H Activation Cascade

An intramolecular Pd-catalyzed cascade reaction is presented that consists of a formal anti-carbopalladation of a C-C triple bond followed by C-H activation. As a result, oligocyclic ring systems with an embedded tetrasubstituted double bond are formed. The key to success in affording the trans geometry of the emerging double bond are alkyne units with residues that must not undergo β-hydride elimination (e.g., t-butyl or silyl groups). Silyl groups proved to be a perfect handle to further convert the tetrasubstituted alkenes. The evaluation of kinetic data with a deuterium-labeled compound and X-ray analyses of trapped intermediates provided additional insight into the catalytic cycle.

Enantioselective Total Synthesis of (+)-Lysergol: A Formal anti-Carbopalladation/Heck Cascade as the Key Step

The enantioselective synthesis of (+)-lysergol was completed in 12 steps and an overall yield of 13% starting from a known literature precursor. The key step relies on a domino reaction containing a formal anti-carbopalladation, which is terminated by a β-silyl-directed Heck reaction. During this transformation, the two six-membered rings of the ergot scaffold are formed in a completely stereospecific manner.

Carbopalladation Cascades Using Carbon-Carbon Triple Bonds: Recent Advances to Access Complex Scaffolds

Alkynes are one of the most versatile functional groups as synthetic handles. They allow for a direct access to partially or fully substituted alkenes through difunctionalization reactions. A prominently utilized transformation for these sequences is the carbopalladation of alkynes, which can be followed by various termination steps such as aromatizations, dearomatizations, cross-coupling reactions, or pericyclic processes, amongst others. This Minireview provides an overview of the recent literature published in the field of carbopalladation chemistry, both with a focus on methodology as well as its application in the syntheses of complex molecular scaffolds, natural products, and functional molecules.

Pd(0)-catalyzed domino C-N coupling/hydroamination/C-H arylation reactions: efficient synthesis and photophysical properties of azaindolo[1,2-f]phenanthridines

A series of new 7- and 4-azaindolo[1,2-f]phenanthridines were synthesized by a domino Pd(0)-catalyzed reaction, which involves three sequential steps: C-N coupling, hydroamination, and intramolecular C-H arylation. The products show promising fluorescence properties with high quantum yields (12-65%).