Site-predictable and chemoselective C–H bond functionalization
reactions offer synthetically powerful strategies for the step-economic
diversification of both feedstock and fine chemicals. Many transition-metal-catalyzed
methods have emerged for the selective activation and functionalization
of C–H bonds. However, challenges of regio- and chemoselectivity
have emerged with application to highly complex molecules bearing
significant functional group density and diversity. As molecular complexity
increases within molecular structures the risks of catalyst intolerance
and limited applicability grow with the number of functional groups
and potentially Lewis basic heteroatoms. Given the abundance of C–H
bonds within highly complex and already diversified molecules such
as pharmaceuticals, natural products, and materials, design and selection
of reaction conditions and tolerant catalysts has proved critical
for successful direct functionalization. As such, innovations within
transition-metal-catalyzed C–H bond functionalization for the
direct formation of carbon–carbon bonds have been discovered
and developed to overcome these challenges and limitations. This review
highlights progress made for the direct metal-catalyzed C–C
bond forming reactions including alkylation, methylation, arylation,
and olefination of C–H bonds within complex targets.
The asymmetric synthesis of chiral polycyclic ethers by an intramolecular [2+2] photocycloaddition is described. This process proceeded through a photocatalitically active iminium ion-based charge transfer (CT) complex under visible light...
We discuss recent advances in the applications of cycloruthenated complexes in organic synthesis, comprising C–H activation, chiral-at-metal catalysis, Z-selective olefin metathesis, transfer hydrogenation, enantioselective cyclopropanations and cycloadditions.
An iron‐catalyzed Kumada‐type cross‐coupling reaction of propargyl halides with alkylmagnesium reagents is described. The reaction is fast, takes place in smooth conditions, tolerates several functional groups that would be able to react with the Grignard reagent, and may afford either allene or propargyl coupling derivatives. Factors involved in the observed regioselectivity have been studied.
Site-selective installation of C−Me bonds remains a powerful and sought-after tool to alter the chemical and pharmacological properties of a molecule. Direct C−H functionalization provides an attractive means of achieving this transformation. Such protocols, however, typically utilize harsh conditions and hazardous methylating agents with poor applicability toward late-stage functionalization. Furthermore, highly monoselective methylation protocols remain scarce. Herein, we report an efficient monoselective, directed ortho-methylation of arenes using N,N,N-trimethylanilinium salts as noncarcinogenic, bench-stable methylating agents. We extend this protocol to d 3 -methylation in addition to the late-stage functionalization of pharmaceutically active compounds. Detailed kinetic studies indicate the rate-limiting in situ formation of MeI is integral to the observed reactivity.
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