Pd-catalyzed regio-divergent annulation of N-(2-methylallyl)carboxamides: access to diverse heterocyclic frameworks
M Jhansi Rani1, N Dastagiri Reddy1
1Department of Chemistry, Pondicherry University, Pondicherry 605014, India. ndreddy.che@pondiuni.ac.in.
Abstract:
A divergent synthetic strategy has been developed for the efficient construction of three distinct heterocyclic frameworks: polycyclic isoquinolinones, phenanthridinones, and cyclopropanated isoquinolinones from N-alkyl/N-aryl-N-(2-methylallyl)carboxamides via palladium-catalyzed Heck/C-H activation reactions. The N-heterocyclic carbene (NHC)-ligated palladacycle complex\[Pd(C^C:)(PPh3)Cl] demonstrated high catalytic efficiency in promoting intramolecular Heck and subsequent two-fold C(sp2)-H activation, affording tetracyclic fused isoquinolinones in good to excellent yields. Interestingly, the use of Pd(PPh3)2Cl2 in combination with pivalic acid and [HPCy3]BF4 selectively directed N-aryl-N-(2-methylallyl)carboxamides toward intramolecular ortho-C(sp2)-H activation, yielding phenanthridinones. Additionally, cyclopropane-fused isoquinolinones and spirocyclopropaisoquinolinones were successfully synthesized through methylene and methyl (proximal or distal) C(sp3)-H activations by using [Pd(PPh3)2Cl2]/Pd(PPh3)4 as the catalyst. Plausible mechanistic pathways leading to these heterocycles are discussed.
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