Palladium‐Catalyzed Formation of C=C Bonds: A Regioselective Strategy for the Synthesis of 2‐Vinylfurans by 1,2‐H Shift of Palladium–Carbene Complexes

Abstract

A convenient method to synthesize vinylfurans through a palladium‐catalyzed cyclization/1,2‐H shift sequence under mild conditions is described. This is an efficient strategy to synthesize 2‐vinylfurans from ene–yne ketones, and the corresponding products are obtained in good yields.

Neue Ansätze für die Synthese von Metallcarbenen

“…Zeitgleich beschrieben Cao et al. eine Palladium‐katalysierte Synthese der 2‐Vinylfurane 476 über einen Prozess mit einer abschließenden 1,2‐H‐Verschiebung des Palladiumcarben‐Intermediats 479 . Wang et al.…”

AgOTf/I2-Mediated Cyclization/Cross-Coupling/Isomerization of Enynones with Phosphorus Ylides: An Expedient Route to Stereoselective Synthesis of (E)-2-Alkenylfurans

“…A small amount of achievement in the field of 2-olefination synthesis has been made. The following three protocols have been disclosed: (1) 1,2-H shift of metal-carbenoid (Scheme a); (2) intramolecular elimination reaction, such as cyclization/elimination of conjugated ene-yne-ketones containing a leaving group (hydroxyl or alkoxy group) at the 6-position, and the elimination of iodonium ylides bearing β-H (Scheme b,c); (3) intermolecular cross-coupling reaction, for example, Pd­(II)-mediated oxidative cross-coupling reaction of conjugated ene-yne-ketones with halogenated hydrocarbon by utilizing benzoquinone as the oxidant (Scheme d), dimerization of conjugated ene-yne-ketones, cross-coupling between two carbene sources such as diazo compounds and ene-yne-ketones for the formation of ( Z )-isomers (Scheme e), and silver­(I)-catalyzed cascade reaction involving enynone cyclization and cross-coupling with iodonium ylides for the construction of the 2-alkenylfuran frame bearing two strong electron-withdrawing groups at the same carbon of the CC double bond (Scheme f) . The intermolecular cross-coupling process comprises cyclization of the enynone followed by coupling with partners, resulting in new C–O and CC bond formation.…”

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

“…Metal carbenes, in many cases converted from vinyl metal species, are often proposed as key intermediate in these transformations 9 10 . In the past 15 years, the transition-metal-catalysed cycloisomerization of ene–yne–ketones has been well established, and provides a safe, effective and practical alternative to the diazo decomposition route for metal carbene generation 11 12 13 14 15 16 17 18 19 20 21 22 23 . In the transformations, the metal π-activated alkyne is attacked by the carbonyl oxygen through 5- exo -dig cyclization to generate zwitterionic vinyl metal intermediate A that could be transformed into its resonance structure, metal (2-furyl)carbene intermediate B ( Fig.…”

“…In the transformations, the metal π-activated alkyne is attacked by the carbonyl oxygen through 5- exo -dig cyclization to generate zwitterionic vinyl metal intermediate A that could be transformed into its resonance structure, metal (2-furyl)carbene intermediate B ( Fig. 1b , M=Cu 19 22 , Au 18 23 , Rh 13 15 , Zn 17 18 and Pd 20 21 ). Metal carbene B subsequently undergoes a variety of transformations, such as oxidation, C-H insertion, cyclopropanation and heteroatom (N, O, Si, S)-H insertion reaction 11 12 13 14 15 16 17 18 19 20 21 22 23 .…”

“…1b , M=Cu 19 22 , Au 18 23 , Rh 13 15 , Zn 17 18 and Pd 20 21 ). Metal carbene B subsequently undergoes a variety of transformations, such as oxidation, C-H insertion, cyclopropanation and heteroatom (N, O, Si, S)-H insertion reaction 11 12 13 14 15 16 17 18 19 20 21 22 23 . Recently, the groups of Zhang 18 and Jiang 19 reported that both Au(I) and Cu(I) (2-furyl)carbenes ( B with M=Au(I) or Cu(I)) can undergo carbene oxidation to give 2-acylfurans ( Fig.…”