Letter pubs.acs.org/OrgLett
Palladium-Catalyzed Multicomponent Reactions of o‑Alkynylanilines, Aryl Iodides, and CO2 toward 3,3-Diaryl 2,4-Quinolinediones Bingbing Wang, Song Sun, Jin-Tao Yu, Yan Jiang, and Jiang Cheng* School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, and Institute for Natural and Synthetic Organic Chemistry, Changzhou University, Changzhou 213164, P. R. China S Supporting Information *
ABSTRACT: Palladium-catalyzed multicomponent reactions (MCRs) between o-alkynylanlines, aryl iodides, and atmospheric pressure of CO2 are developed, affording a series of 3,3-diaryl 2,4-quinolinediones bearing a newly constructed quaternary carbon center in moderate to excellent yields. The reaction proceeded with a sequential carboxylation, trans-oxopalladation of CC bond by ArPdX species, and reductive elimination procedure leading to benzoxazine-2-ones bearing tetrasubstituted vinyl fragments. Then, rearrangement of benzoxazine-2-ones took place toward 3,3-diaryl 2,4-quinolinediones. This procedure features simultaneous formation of four bonds in one pot. ecently, the chemical fixation of CO2 into value-added organic compounds has drawn much attention due to the great potential of CO2 as an abundant, nontoxic, easily available, and renewable C1 building block in organic synthesis.1−3 Among such processes, the n-exo dig (n = 5, 6) cyclization of alkynes with CO2 allows the formation of vinyl-M intermediates bearing heterocyclized frameworks (Scheme 1).
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Due to our continuous study on the transformation of CO2,9 we envisioned developing palladium-catalyzed MCRs involving CO2 toward tetrasubstituted vinyl fragments, which would take part in further transformation to the final product with diversity. We report herein palladium-catalyzed MCRs between o-alkynylanlines, aryl iodides, and atmospheric pressure of CO2, affording a series of 3,3-diaryl 2,4-quinolinediones bearing a newly constructed quaternary carbon center (Scheme 1, path c). 2,4-Quinolinedione frameworks are important heterocyclic structures in medicinal chemistry, serving as an antagonist for the glycine site of NMDA receptors.10 We initially tested the reaction of 2-(phenylethynyl)aniline 1a, phenyl iodide 2a, and atmospheric pressure CO2 in DMSO under 60 °C in the presence of a catalytic amount of Pd(PPh3)2Cl2 and 3 equiv of Cs2CO3. To our surprise, 3,3diphenyl 2,4-quinolinedione 4aa rather than benzoxazine-2-one 3aa was unprecendently isolated in 45% yield (Table 1, entry 1). CO2 was formally cleaved into two parts: one is a carbonyl and the other is an oxygen atom, indicating the involvement of a rearrangement pathway. Pd(0) species, such as Pd2(dba)3 (
