Palladium-catalyzed cascade metallo-ene/Suzuki coupling reaction of allenamides

Abstract

A new type of cascade metallo-ene/Suzuki coupling reaction of allenamides catalyzed by palladium is described. A variety of polyfunctionalized 2,3-dihydropyrrole derivatives, which are important structural motifs for bioactive molecules, were furnished with excellent yields. Two new Csp-Csp bonds were constructed in one pot efficiently. The reductive elimination from π-allyl palladium complex presented excellent regioselectivity to the terminal C1 position. The unique terminal alkene was one of the most easily functionalized groups, providing these molecules with a potential transformation to much more complicated molecules.

Size-Dependent Catalytic Activity and Fate of Palladium Nanoparticles in Suzuki–Miyaura Coupling Reactions

“…Among different C–C coupling reactions, Suzuki–Miyaura is an efficient one − because handling and removal of reagents and products are easy compared to those of the corresponding compounds in organometallic reactions. − Moreover, the reaction is not affected by the number of functional groups present in aryl halides or arylboronic acids. Pd-catalyzed C–C and carbon–heteroatom coupling reactions are performed mostly by expensive, toxic, and air-sensitive P- and/or N-donating ligands like tetrakis­(triphenylphosphine)­palladium(0), tris­(dibenzylideneacetone)­dipalladium(0) in organic solvents, and poly­(2-oxazoline) palladium carbine complex in water or by in situ reduction of Pd­(II) complexes. − The separation of products from these catalysts is very difficult, which seems to be the major drawback of the method.…”

Pd‐Catalyzed Cascade Metallo‐Ene Cyclization/Metallo‐Carbene Coupling of Allenamides

“…As shown in Scheme 1, in the presence of palladium(0) species, the allenamides A could generate two π‐allyl palladium intermediates B and B’ with C sp 3 −C sp 2 bond formation via Metallo‐ene transformation. Based on intermediates B and B’ , we have applied Suzuki coupling and Sonogashira coupling to capture the intermediates to construct 2,3‐2H‐pyrrole derivates ( I ) and ( II ) bearing aromatic or alkynyl groups [13b–c] . To further explore, novel methodologies to construct functionalized pyrroles, we continued to consider the transformation of intermediate B and B’ .…”

Palladium‐Catalyzed Intramolecular Alder‐Ene Type Cycloisomerization Reactions

“…In 2017, Dong and Liu demonstrated a proficient one-pot construction of diversely substituted 2,3-dihydropyrroles 29 via a cascade palladium-ene/Suzuki reaction sequence of allenamides 28 in excellent yield and high levels of regioselectivity with respect to the pyrrolidine double bond (Scheme 16). [20] The proposed mechanism involves the formation of (η 3 -allyl)palladium species AK via the oxidative addition of 28 upon treatment with a catalytic amount of Pd (II) complex. The π-allyl species AK then undergoes palladium-ene reaction to give AL.…”