Palladium‐Catalyzed Oxidative Alkynylation of Allenyl Ketones: Access to 3‐Alkynyl Poly‐substituted Furans^†

Abstract

Comprehensive SummaryFurans bearing alkynyl substituents are highly useful in organic synthesis. However, the methodologies to access these important furan derivatives are rather limited. We herein report an efficient synthesis of alkynylated furan derivatives based on Pd‐catalyzed oxidative cross‐coupling reaction between allenyl ketones and terminal alkynes. This novel synthesis of alkynylated furans with wide substrate scope is operationally simple and tolerates various functional groups. Mechanistically, the formation of the palladium carbene through cycloisomerization and the subsequent alkynyl migratory insertion are proposed as the key steps in the transformation. The reaction reported in this manuscript further demonstrates the generality of the carbene‐based cross coupling.This article is protected by copyright. All rights reserved.

Palladium-Catalyzed Domino Heck/Cross-Coupling Cyclization Reaction: Diastereoselective Synthesis of Furan-Containing Indolines

“…A possible mechanism based on the experimental evidence and previous studies is proposed (Scheme ). Oxidative addition of N -arylacyl indole 1a and an intramolecular syn -migratory insertion generate the secondary benzyl–palladium(II) species B .…”

“…Besides, cross-couplings employing 1,2-allenyl ketones as nondizao carbene precursors through Pd-carbene migratory insertion to construct polysubstituted furan derivatives are particularly fascinating but scarcely developed. To date, only few cross-couplings using 1,2-allenyl ketones as the carbene precursors under Pd-catalysis have been reported (Scheme e) . In the past decade, Wang’s group developed the palladium-promoted oxidative cross-coupling of organoboronic acids with allenyl ketones, cyclizative borylation of allenyl ketones, and alkynylation of allenyl ketones, affording tri- and tetra-substituted furans, trisubstituted 3-furyl boronates, and 3-alkynyl polysubstituted furan derivatives, respectively.…”

Intermolecular Allene–Alkyne Coupling: A Significantly Useful Synthetic Transformation

“…In a related cyclizative alkynylation method, Wang and colleagues devised an atom-economy procedure involving allenyl ketones ( 56a ) and terminal alkynes ( 56b ), employing a Pd catalyst (Scheme ). Notably, the electron-deficient catalyst system in combination with stoichiometric amount of the oxidant 2,5-dimethylbenzoquinone (2,5-DMBQ) enabled the cascade cycloisomerization/alkyne interception via alkynyl migratory insertion. This transformation was realized under a familiar mechanistic picture involving carbene migratory insertion strategy, affording C3-alkynylated furan derivatives ( 56c ) in good yield, wherein an electron-deficient catalyst system is more likely to facilitate both transmetalation and cyclization events.…”