Pd^II‐Catalyzed Cascade Synthesis of Chromane Derivatives Initiated by cis‐Chloropalladation or trans‐Acetoxypalladation

Abstract

A highly regio‐ and stereoselective PdII‐catalyzed cascade synthesis of biologically relevant chromane derivatives from easily available enynes was developed under operationally simple conditions. The cascade reaction consists of nucleopalladation of alkynes, insertion of the alkene and protonation. When CuCl2 was employed as nucleophile, a cis‐chloropalladation initiates the cascade. Whereas in the case of AcOH, a trans‐acetoxypalladation takes place.

Palladium-Catalyzed Regioselective Syn-Chloropalladation–Olefin Insertion–Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

“…Initial coordination of alkyne 1 with PdCl 2 followed by syn -chloropalladation would generate σ-vinylpalladium intermediate B via palladium-coordinated species A , which would successively undergo olefin insertion with the pendant α,β-unsaturated carbonyl moiety to deliver the Pd II tetrahydroquinoline intermediate C ( E isomer). In the presence of water, as demonstrated in Scheme , eqs 2–4, the monochloro derivative 3 has formed via protonation after regenerating the Pd II intermediate . However, in our optimized experimental conditions, in the absence of water, no protonation takes place to yield the monochloro compound 3 .…”

Synthesis of Highly Conjugated Functionalized 2-Pyridones by Palladium-Catalyzed Aerobic Oxidative Dicarbonation Reactions of N-(Furan-2-ylmethyl) Alkyne Amides and Alkenes as Coupling Partners

“…On the basis of the above-described results and previously reported results for Pd-catalyzed difunctionalization of alkynes, − a plausible route for this transformation is illustrated in Scheme . The reaction is initiated by coordination of Pd­(II) with the triple bond of alkyne 1 to afford π-complex I .…”

“…Pd-catalyzed difunctionalization of alkynes is a powerful method for preparing N -heterocyclic compounds (Scheme a). This method involves nucleopalladation of the alkyne with a nucleophile (such as acetic acid, an amide or amine, a halide or pseudohalide, a carbonyl oxygen, a boronic acid, or an electronic-rich alkene) to generate vinylpalladium species A , which is captured by another nucleophile or an electrophile. Varying the nucleophile(s) or the electrophile allows for the synthesis of a diverse array of structurally novel products.…”

LiCl-Mediated and Palladium-Catalyzed Oxidative Cyclization of Furan–Ynes via Dearomatizing Alkoxyalkenylation of Furan

“…During this process, alkynes could react with various nucleophiles and generate diverse vinylpalladium species, which are prone to Heck-type insertion with alkenes (Scheme a) . Since Lu’s seminal reports of 1,6-enyne cyclization initiated by chloropalladation, , this type of cyclization has been extensively developed by Zhang, Liu, Volla, Qiu, Liu, and Sridharan . Mechanistically, chloropalladation-initiated enyne cyclization falls into two groups: redox–neutral cyclization , and oxidative cyclization. ,− These chloropalladation-initiated oxidative cyclization reactions of enynes are mostly focused on enynes with activated alkene units.…”

“…Since Lu’s seminal reports of 1,6-enyne cyclization initiated by chloropalladation, , this type of cyclization has been extensively developed by Zhang, Liu, Volla, Qiu, Liu, and Sridharan . Mechanistically, chloropalladation-initiated enyne cyclization falls into two groups: redox–neutral cyclization , and oxidative cyclization. ,− These chloropalladation-initiated oxidative cyclization reactions of enynes are mostly focused on enynes with activated alkene units. Due to inherent nucleophilicity and inferior oxidative resistance of electron-rich alkenes; however, chloropalladation-initiated oxidative cyclization of enynes with unactivated electron-rich alkene units, such as furan, remains significantly underexplored.…”