Privilege Ynone Synthesis via Palladium-Catalyzed Alkynylation of “Super-Active Esters”
摘要:
A neat palladium-catalyzed alkynylation reaction was developed with "super-active ester" as the carbonyl electrophile, which provides a dean-and efficient synthetic protocol for a broad array Of ynone compounds under CO-, Cu-,, ligand-, and base-free conditions. The superior activity of triazine ester was rationalized by the strong electron;withdrawing ability and the unique affinity of triazine On palladium. A mechanistic experiment clearly demonstrated that the N-Pd coordination of triazine plays a crucial role for the highly efficient C-O activation.
Lewis base, N-methylmorpholine (NMM) accelerated Pd-catalyzed Sonogashira coupling of steric hindered super active esters, la-le, and terminal alkynes. This approach provided an efficient synthetic protocol for a broad array of acylated o-alkynoylphenols compounds, 3a-3e, under moderate conditions. The mechanistic study clearly demonstrated that NNM stabilized the catalytic palladium species, and accelerated the leaving of triazine moiety during the catalytic cycle of the cross-coupling reactions. In addition, piperazine was found to efficiently catalyze the 6-endo cyclization of acylated o-alkynoylphenols, which achieved the diversity oriented synthesis of gamma-benzopyranones, 4aa-4eg, with 93-99% yields. (C) 2016 Elsevier B.V. All rights reserved.