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10.1002/ejoc.201801532
European Journal of Organic Chemistry
COMMUNICATION
Ruthenium-Catalyzed C-H Selenylations of Benzamides
Wenbo Ma,*[a] Zhengyun Weng,[a] Xinyue Fang,[a] Linghui Gu,[a] Yupin Song,[b] Lutz Ackermann*[c]
Abstract: A convenient and effective protocol for the ruthenium-
catalyzed C-H selenylations of benzamides was achieved under mild
reaction conditions. The robust ruthenium catalyst tolerated a wide
range of functional groups and set the stage for the preparation for
diversely decorated benzamides. The amide directing group could be
transferred to carboxylic acid, aldehyde and tetrazoles. Preliminary
were often accompanied by the difficult to remove diselenylated
products,[14] with in some cases due to the poor regio-selectivity.
Furthermore, many of these directing groups are difficult to
remove or modify, thus limiting the further transformation in the
complex compound synthesis. As a consequence, there is a
directing group-assisted C−H. Amides are ubiquitous structural
motifs which were widely found in numerous biologically active
natural products and pharmaceutical compounds.[15] In addition,
the amide group likewise represents a versatile functional group
that can be easily converted into various useful functional groups,
including tetrazoles, carboxylic acids or aldehydes.[16]
mechanistic study indicated
a base-assisted electrophilic-type
substitution C-H activation event.
Introduction
Diaryl selenide scaffolds are important structural motifs that have
attracted increasing interest as functional organic materials, drug
candidates and biologically active compounds.[1] Furthermore,
they also play an important role in fluorescent probes as well as
coordination chemistry, and they are widely used in organic
synthesis.[2] Therefore, the preparation of diaryl selenide scaffolds
has attracted considerable interest in the past decades.[3] The
traditional methods for their syntheses largely involved the use of
electron-rich arenes or prefunctionalized aryl (pseudo)halides as
the coupling partners.[4] However, most of these approaches
usually required multi-step protocols under harsh reaction
conditions, thus resulting in low overall yields with various
functional groups being incompatible. In contrast, the transition-
metal-catalyzed C−Se formation via direct C−H activation
represents a powerful and reliable alternative due to its
remarkable mild reaction conditions, broad substrate scope, step-
economic fashion and environmental sustainability.[5]
In continuation of our interest on the research of C−S and C−Se
bond forming reactions using the ruthenium catalyzed C-H
functionalization strategy,[12],[17] and considering the synthetic
utility of amides, we herein report on the unprecedented
ruthenium-catalyzed highly selective mono-selenylation of
benzamides. (Scheme 1b)
In this context, transition metals such as palladium, rhodium,
ruthenium, silver, nickel, cobalt and copper complex were
explored as catalysts for the chelation-assisted C−H selenylations
during the past decade.[6] Thereby, the chelation assistance
regime could recently be expanded to pyrimidine,[7] pyrazole,[8]
pyridine,[9] oxime,[10] carboxylate acid,[11] anilide[12] and bidentate
auxiliaries.[13] These protocols provided efficient and convenient
routes for the direct assembly of diaryl selenide scaffolds.
(Scheme 1a) However, the desired mono-selenylated products
Scheme 1. Transition-metal-catalyzed C−H Chalcogenations of Arenes
[a]
Prof. Dr. Wenbo Ma, Zhengyun Weng, Xinyue Fang, Dr. Linghui Gu,
Antibiotics Research and Re-evaluation Key Laboratory of Sichuan
Province, Sichuan Industrial Institute of Antibiotics, Chengdu
University, People’s Republic of China, 610052.
[b]
[c]
Yupin Song
Results and Discussion
College of Engineering, Shijiazhuang University, P. R. China.
Prof. Dr. Lutz Ackermann
Institut fuer Organische und Biomolekulare Chemie, Georg-August-
Universitaet, Goettingen, Germany
We commenced our studies by examining the reaction
parameters for the envisioned direct C−H selenylation of
benzamide (1a) with 1,2-diphenyldiselane (2a). Preliminary
experiments indicated [RuCl2(p-cymene)]2 as the appropriate
catalyst, along with catalytic amount of AgSbF6 and AgOTf as the
additives at 100 °C for 20 h (Table 1, entry 1). Further optimization
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