Abstract
An efficient and convenient method to construct tetracyclic isoquinolinium salts via [Cp*RhCl2]2 catalyzed C–H activation and [4 + 2] annulation reactions in ethanol is described. This reaction is very fast and highly efficient in the green solvent ethanol. The reaction works with a broad substrate scope affording the products in good to excellent yields in a short time. Moreover, a ratio of S/C up to 10 000 could be achieved with gram scale synthesis.
Highlights
N-Heterocyclic quaternary ammonium salts and their derivatives are versatile heterocyclic compounds found in many natural[1] and synthetic products[2] and are well-known for their potent biological activities[3] (Fig. 1)
Signi cant advancements have been made in transition-metal-catalyzed C–C bond formation via C–H activation, among which rhodium-catalyzed direct C–H bond activations are powerful strategies to synthesize various polycyclic skeletons and N-heterocyclic scaffolds, due to their high efficiency and atom economy.[4]
We proposed that it was possible to use the imine group of dihydroisoquinoline as a directing group to furnish C–H activation and [4 + 2] annulation to construct tetracylic isoquinolinium salts
Summary
N-Heterocyclic quaternary ammonium salts and their derivatives are versatile heterocyclic compounds found in many natural[1] and synthetic products[2] and are well-known for their potent biological activities[3] (Fig. 1). We report Rh-catalyzed [4 + 2] annulations of cyclic-imine of 1phenyl-3,4-dihydroisoquinolines to synthesis tetracyclic isoquinolinium salts in ethanol. At the outset of our study, [Cp*RhCl2]2 was used to catalyze 6,7dimethoxy-1-phenyl-3,4-dihydroisoquinoline 1a with diphenylacetylene 2a to investigate the catalytic performance of additives, solvents, and oxidants (Table 1).
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