Conversion of Triple Bonds into Single Bonds in a Domino Carbopalladation with Norbornene

Abstract

A domino carbopalladation reaction of haloalkynes is presented. Remarkably, the four-time carbopalladation process converts the carbon-carbon triple bonds of haloalkynes stepwise into carbon-carbon double bonds, and finally to carbon-carbon single bonds. Features of this reaction are that the carbon-carbon double bonds of stable vinyl palladium intermediates are transformed into carbon-carbon single bonds with the generation of unstable alkyl palladium intermediates. The subsequently formed π-allylpalladium species are independently trapped by N-tosylhydrazones, boronic acids, and B pin in a highly diastereoselective manner, delivering the corresponding polycyclic and twisted products with a bicyclo[3.2.1]oct-2-en-3-yl)tricyclo[3.2.1.0 ]octane core skeleton in moderate to good yields via C-C and C-B bond formations. Significantly, the dual roles of norbornenes, ring construction and ring expansion, and the identification of electron-rich tri(2-furyl)phosphine as the ligand are found to be critical for the success of these transformations.

Recent Development in Palladium-Catalyzed Domino Reactions: Access to Materials and Biologically Important Carbo- and Heterocycles

“…The stable vinyl palladium intermediates were transformed into carbon–carbon single bonds with the generation of unstable alkyl palladium intermediates, which afforded a ring expansion forming π-allylpalladium species. Last intermediates could be independently quenched by boronic acids as terminating step (Scheme ), or N -tosylhydrazones, or B 2 (pin) 2 in a highly diastereoselective manner and very good yields (47–73%) . Norbornene also participated in an efficient, highly regio- and stereoselective protocol for the synthesis of tetrasubstituted olefins.…”

“…Last intermediates could be independently quenched by boronic acids as terminating step (Scheme 18), or N-tosylhydrazones, or B2(pin)2 in a highly diastereoselective manner and very good yields (47-73%). 27 Norbornene also participated in an efficient, highly regio-and stereoselective protocol for the synthesis of tetrasubstituted olefins. The process was developed through a palladium(0)-catalyzed triple domino process involving an alkene relay-intramolecular alkyne relay system.…”

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

“…In 2017, Wu and Jiang reported a Pd-catalyzed, three-component coupling of alkynyl bromides 62 , norbornene derivatives 15 , with electrophilic trapping agents ( Scheme 49 ) [ 105 ]. Mechanistically, the transformation begins with the oxidative addition of the alkynyl bromide to the Pd(0) catalyst.…”