Cascade catalysis of bis-PNP-ligand-modified Pd-catalyst for three-step aminocarbonylation-methoxycarbonylation-cyclization tandem reaction for synthesis of N-substituted succinimides from terminal alkynes

A series of base-built-in-PNP-ligands (L1-L4) were synthesized and fully characterized. The synthesis methodology for these ligands were simple and efficient without involvement of high-risky BuLi or high-cost transition metal catalysts. With the aid of the pyrazinyl-tertiary amine-based bis-PNP ligand of L1, in the coexistence of the nucleophiles of amine and MeOH, the terminal alkynes smoothly converted to N-substituted succinimides in moderate to excellent isolated yields, via one-pot three-step tandem reaction in aminocarbonylation-methoxycarbnylation-cyclization sequence. The developed L1-Pd(MeCN)₂Cl₂ catalyst exhibited typical cascade catalysis with divergent performance towards each individual reaction-step. And the second-step methoxycarbonylation of the branched α,β-unsaturated amides towards ω-amido esters was a decent detour for the successful production of N-substituted succinimides from alkynes, CO and primary amines.