Substrate Self-Assisted Secondary Bond Activation of Allylic Alcohol in a Tsuji–Trost Reaction Revealed by NMR Methods

We report selective formation of heterobimetallic PtII/CuI complexes that demonstrate how facile bond activation processes can be achieved by altering reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with Pt center and with a Pt-bound alkyl group increases the stability of PtMe2 towards undesired rollover cyclometalation. The presence of the CuI center also enables facile transmetalation from electron-deficient tetraarylborate [B(ArF)4]- anion and mild C-H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the role of Cu center acts as a binding site for alkyne substrate, while activating its terminal C-H bond.

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Imine as a Linchpin Approach for Distal C(sp2)–H Functionalization

10.26434/chemrxiv.11521827 ◽

2020 ◽

Author(s):

Sukdev Bag ◽

Sadhan Jana ◽

Sukumar Pradhan ◽

Suman Bhowmick ◽

Nupur Goswami ◽

...

Keyword(s):

Organic Molecules ◽

Bond Activation ◽

Bond Formation ◽

Ancillary Ligand ◽

Significant Challenge ◽

Site Selectivity ◽

Directing Group ◽

Covalently Linked ◽

Complex Organic ◽

Post Functionalization

Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing group (DG) served as an ancillary ligand to ensure proximal ortho-, distal meta- and para-C-H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. We introduce here a transient directing group for distal C(sp2)-H functionalization via reversible imine formation. By overruling facile proximal C-H bond activation by imine-N atom, a suitably designed pyrimidine-based transient directing group (TDG) successfully delivered selective distal C-C bond formation. Application of this transient directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the distal position has been explored.

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Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

10.26434/chemrxiv.11145098 ◽

2019 ◽

Author(s):

Raghu Nath Dhital ◽

keigo nomura ◽

Yoshinori Sato ◽

Setsiri Haesuwannakij ◽

Masahiro Ehara ◽

...

Keyword(s):

Activation Energy ◽

Low Temperature ◽

Dft Calculations ◽

Bond Activation ◽

Mild Conditions ◽

Selective Transformation ◽

Rate Determining Step ◽

Highly Active ◽

Harsh Conditions ◽

Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the beta-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

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Synthesis of the C19–C30 Bis-THF Fragment of Iriomoteolide-13a via Stepwise SN2 Cyclization and Intramolecular syn-Oxypalladation

10.26434/chemrxiv.13506678.v1 ◽

2020 ◽

Author(s):

Hui Zhao ◽

Kai Gao ◽

Haichen Ma ◽

Tsz Chun Yip ◽

Wei-Min Dai

Keyword(s):

Aldol Reaction ◽

Allylic Alcohol ◽

Asymmetric Dihydroxylation ◽

Hydroxy Groups

The C19–C30 bis-THF fragment of the proposed structure of iriomoteolide-13a has been synthesized. The w-mesyloxy-substituted stereotetrad possessing three continuous hydroxy groups was generated by anti-aldol reaction and asymmetric dihydroxylation (AD). Upon heating in pyridine the stereotetrad underwent an SN2 cyclization to form the C19–C22 THF ring. It was followed by an intramolecular syn-oxypalladation of the C28 chiral allylic alcohol to give the C23–C26 THF ring.

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Carbon Dioxide-Mediated C(sp2)–H Arylation of Primary and Secondary Benzylamines

10.26434/chemrxiv.7138088.v2 ◽

2018 ◽

Author(s):

Mohit Kapoor ◽

Pratibha Chand-Thakuri ◽

Michael Young

Keyword(s):

Carbon Dioxide ◽

Transition Metal ◽

Bond Activation ◽

Bond Formation ◽

Carbon Bond ◽

Chelate Effect ◽

Free Amine ◽

Carbon Carbon Bond ◽

New Strategy ◽

Metal Catalyzed

Carbon-carbon bond formation by transition metal-catalyzed C–H activation has become an important strategy to fabricate new bonds in a rapid fashion. Despite the pharmacological importance of ortho-arylbenzylamines, however, effective ortho-C–C bond formation from C–H bond activation of free primary and secondary benzylamines using PdII remains an outstanding challenge. Presented herein is a new strategy for constructing ortho-arylated primary and secondary benzylamines mediated by carbon dioxide (CO2). The use of CO2 is critical to allowing this transformation to proceed under milder conditions than previously reported, and that are necessary to furnish free amine products that can be directly used or elaborated without the need for deprotection. In cases where diarylation is possible, a chelate effect is demonstrated to facilitate selective monoarylation.

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