Dioxygen activation under ambient conditions: cu-catalyzed oxidative amidationdiketonization of terminal alkynes leading to -ketoamides

Dioxygen Activation under Ambient Conditions: Cu-Catalyzed Oxidative
Amidation-Diketonization of Terminal Alkynes Leading to r-Ketoamides
State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking UniVersity, Xue Yuan Road 38, Beijing 100191, China, and State Key Laboratory of Organometallic Chemistry, Chinese Academy of Received October 19, 2009; E-mail: jiaoning@bjmu.edu.cn Dioxygen is an ideal oxidant and offers attractive academic and Table 1. Cu-Catalyzed Oxidative Amidation-Diketonization of 1a
industrial prospects.1 Significantly, dioxygen activation2 for the func- with Alkyne 2aa
tionalization of an organic molecule has been of long-standing interestto organic chemists because of its tremendous importance in chemistryas well as in biology.3 In the past decades, alkynes have beenextensively used in organic synthesis through transition-metal-catalyzedreactions. Recent breakthroughs involving the cross-dehydrogenativecoupling (CDC)4 reaction of terminal alkynes via C-H activation (eq % yield of 3aab
1) have been developed by the research groups of Stahl,5a Li,5b and Han.5c In these approaches, one new C-N, C-C, or C-P bond, respectively, is formed with retention of the triple C-C bond, facilitated 2.5a,c However, this kind of coupling using molecular oxygen as the oxidant still remains a challenging research area, and the oxidation of alkynes with dioxygen has very rarely been investigated.6 The combination of using dioxygen as the oxidant and 8e
as a reactant via dioxygen activation would substantially broaden thefield of cross-coupling and offer more functionalized products. Herein, a Reaction conditions: 1a (0.25 mmol), 2a (1.25 mmol), cat. (0.025
for the first time, we present a novel Cu-catalyzed oxidative mmol), TEMPO (0.025 mmol), pyridine (1.0 mmol), H2O (2.5 mmol), amidation-diketonization reaction of terminal alkynes using O toluene (3 mL), O2 (1 atm), 18 h. b Isolated yields. c The reaction was carried out in the absence of TEMPO. d The reaction was carried out oxidant and as a reactant via dioxygen activation (eq 2). This chemistry under air. e A 90% yield was obtained when 10 equiv of 2a was used.
offers not only a new approach to R-ketoamides but also valuablemechanistic insights into this novel Cu catalysis.
in our cases could be transformed into the desired products. In
addition, a heteroaryl-substituted alkyne, 3-thienylacetylene (2i),
provided 3ai in 64% yield (Table 2, entry 9). It is noteworthy that
alkenyl-substituted alkynes such as 2l and 2m survived well, leading
to 3al (65%) and 3am (24%), respectively (entries 12 and 13).
The scope of the Cu-catalyzed oxidative amidation-diketonization reaction was further expanded to a variety of substituted anilines 1
(Table 3). These results indicate that anilines with electron-donating
groups proceeded more efficiently than anilines containing electron-
withdrawing groups. It is noteworthy that halo-substituted anilines
During our investigation of indole synthesis via Pd-catalyzed reactions of anilines and alkynes using dioxygen as the oxidant,7a we Table 2. Cu-Catalyzed Oxidative Amidation-Diketonization of 1a
discovered the rather surprising formation of 2-oxo-2-phenyl-N-p- with Alkynes 2a
toylacetamide (3aa) from 4-methylaniline (1a) and phenylacetylene
(2a) when copper salts&#

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