Abstract
The past decades have witnessed rapid development in organic synthesis via catalysis, particularly the reactions through C–H bond functionalization. Transition metals such as Pd, Rh and Ru constitute a crucial catalyst in these C–H bond functionalization reactions. This process is highly attractive not only because it saves reaction time and reduces waste,but also, more importantly, it allows the reaction to be performed in a highly region specific manner. Indeed, several organic compounds could be readily accessed via C–H bond functionalization with transition metals. In the recent past, tremendous progress has been made on C–H bond functionalization via ruthenium catalysis, including less expensive but more stable ruthenium(II) catalysts. The ruthenium-catalysed C–H bond functionalization, viz. arylation, alkenylation, annulation, oxygenation, and halogenation involving C–C, C–O, C–N, and C–X bond forming reactions, has been described and presented in numerous reviews. This review discusses the recent development of C–H bond functionalization with various ruthenium-based catalysts. The first section of the review presents arylation reactions covering arylation directed by N–Heteroaryl groups, oxidative arylation, dehydrative arylation and arylation involving decarboxylative and sp3-C–H bond functionalization. Subsequently, the ruthenium-catalysed alkenylation, alkylation, allylation including oxidative alkenylation and meta-selective C–H bond alkylation has been presented. Finally, the oxidative annulation of various arenes with alkynes involving C–H/O–H or C–H/N–H bond cleavage reactions has been discussed.
Highlights
Synthesis of organic compounds with a heterocyclic ring and natural product scaffolds are extremely important as they form an indispensable structural unit of bioactive compounds and pharmacophores [1,2]
This review describes the recent development on the C–H bond functionalization reactions covering arylation, alkenylation, alkylation and annulation reactions with ruthenium-based catalysts
Catalytic C–H bond functionalization with ruthenium-based catalysts has emerged a powerful method in organic synthesis for ready access to various functional molecules in a greener and time-saving manner
Summary
Synthesis of organic compounds with a heterocyclic ring and natural product scaffolds are extremely important as they form an indispensable structural unit of bioactive compounds and pharmacophores [1,2]. The coupling of arene or alkene with an organometallic reagent requires an oxidant to generate the metal species (Scheme 1c) In both the direct C–H functionalization methods, apre-functionalised starting material is required. The dehydrogenative method involving the coupling of two C–H bonds, first discovered by Moritani and Fujiwara with a Pd catalyst, is the most step-and atom economical process, as it does not require any pre-functionalized starting materials (Scheme 1d). Transition metal-catalysed C–H bond functionalization has rapidly developed and its utility in the synthesis of organic compounds is well documented [10]. The mechanistic study of ruthenium-catalysed C–H bond functionalization was recently described by the research group of Lan [41] in the context of arylation, alkylation and alkenylation,and by Nelson and co-workers on selective ortho-arylation directed by. The review focusses on the developments in this field over the past eight years and includes reports that have appeared up until 2018
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