Construction of Heterocycle Scaffolds via Transition Metal‐ Catalyzed sp² CH Functionalization

Abstract

Recently, the C À H functionalization strategy for the construction of heterocycles has received substantial attention because of its economic, sustainable and environmentally benign features. Many kinds of heterocycles have been synthesized via transition metal-catalyzed sp 2 C À H functionalization. The new strategy for the construction of heterocycle scaffolds includes intramolecular cyclizations and intermolecular cyclizations, namely multicomponent reactions (MCRs) that achieve the formation of multiple bonds in one operation. This review introduces the synthesis of carbazoles, benzoxazoles, benzimid-A C H T U N G T R E N N U N G azoles, 2-substituted benzothiazoles, 3-aryl/alkylind-A C H T U N G T R E N N U N G azoles, indoles, oxindoles, indolines, benzolactams, phthalimides, dibenzofurans and bridgehead unsaturated bicyclic enamines by the new strategy. The orientation of the cyclizations depends mainly on steric factors in cases where two regioisomers can be obtained. The regioselectivity of cyclizations is high in most cases, the cyclizations are even exclusive to give one sole product without the regioisomer in some cases. The functional group tolerance is good in most cases, halogen atoms and even iodine atoms are tolerated by the new strategy in some cases, providing a handle for further functionalization. The described strategy is being rapidly developed. Versatile features of the strategy have emerged, this review tries to classify the reported methods and inspire further investigations.

Asymmetric Synthesis with Silicon‐Based Bulky Amino Organocatalysts

“…When ketones were used as substrates, moderate to good yields were obtained but the enantioselectivities are excellent (up to 99% ee). [20] With realization of the importance of the Mannich reaction in the synthesis of b-amino acid derivatives, Gellman [21a] and Córdova [21b] successfully exploited the enantioselective organocatalytic method for the Mannich reaction between formaldehyde-derived Nbenzyl-N-(methoxymethyl)A C H T U N G T R E N N U N G (phenyl)methanamine (35) and aldehydes. Formaldehyde does not form stable imines, so the use of N-benzyl-N-(methoxymethyl)-A C H T U N G T R E N N U N G (phenyl)methanamine (35) as a precursor of the methylene iminium species is practical.…”

Polystyrene‐supported Pd(II) complex‐catalysed carboacylation of 2‐arylpyridines with alcohols via C─H bond activation under solvent‐free conditions

“…Directing group‐assisted C─H bond functionalization and cross dehydrogenative coupling are commonly employed strategies due to their being atom‐ and step‐economic for achieving selective functionalizations . Transition‐metal‐catalysed C─H activation and subsequent C─H bond functionalization has achieved great progress in modern synthetic chemistry . Ru, Rh, Cu and Pd are commonly employed metals for carbon–carbon bond forming processes .…”

“…[4][5][6] Transition-metal-catalysed C─H activation and subsequent C─H bond functionalization has achieved great progress in modern synthetic chemistry. [7][8][9][10][11] Ru, Rh, Cu and Pd are commonly employed metals for carbon-carbon bond forming processes. [12,13] Palladium complexes are particularly attractive catalysts for ligand-directed C─H functionalization reactions.…”

Pd‐Catalyzed Sequential CC and CN Bond Formations for the Synthesis of N‐Heterocycles: Exploiting Protecting Group‐Directed CH Activation under Modified Reaction Conditions

“…In the search for an atom economical and eco-friendly chemical process, direct activation and subsequent functionalization of C À H bonds in aromatic compounds have attracted significant attention as the method of choice and implicated wide spread synthetic applications. [1] In particular, oxidative cross-coupling reactions between arenes and olefins, commonly known as the Fujiwara-Moritani reaction, [1c, g, 2] is a powerful variant of the classical Mizoroki-Heck reaction [3] that obviates the need for the use of aryl halides and alleviates the generation of salt waste. In general, regioselectivity of the Fujiwara-Moritani reaction can be achieved either through the introduction of a coordinative functionality, [4] or by the use of external ligands.…”