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1.
Org Lett ; 25(3): 483-487, 2023 Jan 27.
Article in English | MEDLINE | ID: mdl-36652608

ABSTRACT

Leveraging α-fluoroalkyl or fluorobenzyl radicals to introduce fluorinated motifs allows for the rapid preparation of fluorine-containing building blocks. Herein, we report the generation of α-fluoroalkyl or fluorobenzyl radicals from readily available α-fluorocarboxylic acids under mild reaction conditions and their utilization in the Giese-type addition on Michael acceptors and dehydroamino acids, resulting in the preparation of mono- and difluorinated Michael addition adducts and unnatural fluorinated amino acids.

2.
Org Lett ; 24(19): 3455-3460, 2022 05 20.
Article in English | MEDLINE | ID: mdl-35544734

ABSTRACT

The cyclopropanation of alkenyl boronates and subsequent derivatization of the boronate handle are a convenient strategy to quickly build molecular complexity and access diverse compounds with a high sp3 fraction. Herein, we describe the asymmetric cyclopropanation of enantioenriched hydrobenzoin-derived alkenyl boronic esters toward the synthesis of tertiary and secondary cyclopropyl boronates.


Subject(s)
Boron , Esters , Boronic Acids , Stereoisomerism
3.
Chem ; 5(2): 339-352, 2019 Feb 14.
Article in English | MEDLINE | ID: mdl-31080910

ABSTRACT

The integration of amidyl radicals with cross-coupling chemistry opens new venues for reaction design. However, the lack of efficient methods for the generation of such radical species has prevented many such transformations from being brought to fruition. Herein, the amidoarylation of unactivated olefins by a cascade process from non-functionalized amides is reported by merging, for the first time, photoredox proton-coupled electron transfer (PCET) with nickel catalysis. This new technology grants access to an array of complex molecules containing a privileged pyrrolidinone core from alkenyl amides and aryl- and heteroaryl bromides in the presence of a visible light photocatalyst and a nickel catalyst. Notably, the reaction is not restricted to amides - carbamates and ureas can also be used. Mechanistic studies, including hydrogen-bond affinity constants, cyclization rate measurements, quenching studies, and cyclic voltammetry were central to comprehend the subtleties contributing to the integration of the two catalytic cycles.

4.
ACS Catal ; 9(9): 8835-8842, 2019 Sep 06.
Article in English | MEDLINE | ID: mdl-34055458

ABSTRACT

Herein, the introduction of oxa- and azabenzonorbornadienes into photoredox/nickel dual catalysis in a regioselective and diastereoselective transformation is disclosed. The inherent advantages of this dual catalytic system allow the use of alkyl motifs forming exclusively cis-1,2-dihydro-1-naphthyl alcohol backbones using readily accessible 4-alkyl-1,4-dihydropyridines (DHPs). Whereas previous studies have emphasized the use of nucleophilic organometallic coupling partners, this protocol grants access to a rather unexplored core featuring alkyl residues, while avoiding the use of highly reactive organometallic species (i.e., M = Al, Mg, Li, Zn, Zr). DFT calculations support a oxidative addition/reductive elimination mechanism, followed by a Curtin-Hammett scenario that controls the regioselectivity of the process, unlike previously reported transformations that proceed via a carbometalation/ ß-oxygen elimination mechanism.

5.
Angew Chem Int Ed Engl ; 57(48): 15847-15851, 2018 11 26.
Article in English | MEDLINE | ID: mdl-30307672

ABSTRACT

A regioselective, nickel-catalyzed photoredox allylation of secondary, benzyl, and α-alkoxy radical precursors is disclosed. Through this manifold, a variety of linear allylic alcohols and allylated monosaccharides are accessible in high yields under mild reaction conditions. Quantum mechanical calculations [DFT and DLPNO-CCSD(T)] support the mechanistic hypothesis of a Ni0 to NiII oxidative addition pathway followed by radical addition and inner-sphere allylation.


Subject(s)
Electrons , Nickel/chemistry , Propanols/chemical synthesis , Catalysis , Molecular Structure , Oxidation-Reduction , Photochemical Processes , Propanols/chemistry , Quantum Theory
6.
Angew Chem Int Ed Engl ; 57(22): 6614-6618, 2018 05 28.
Article in English | MEDLINE | ID: mdl-29573308

ABSTRACT

The development of synthetic tools to introduce saccharide derivatives into functionally complex molecules is of great interest, particularly in the field of drug discovery. Herein, we report a new route toward highly functionalized, arylated saccharides, which involves nickel-catalyzed cross-coupling of photoredox-generated saccharyl radicals with a range of aryl- and heteroaryl bromides, triggered by an organic photocatalyst. In contrast to existing methods, the mild reaction conditions achieve arylation of saccharide motifs while leaving the anomeric carbon available, thus providing access to a class of arylated glycosides that has been underexplored until now. To demonstrate the potential of this strategy in late-stage functionalization, a variety of structurally complex molecules incorporating saccharide moieties were synthesized.


Subject(s)
Nickel/chemistry , Sugars/chemical synthesis , Catalysis , Molecular Structure , Oxidation-Reduction , Photochemical Processes , Sugars/chemistry
7.
J Am Chem Soc ; 139(35): 12251-12258, 2017 09 06.
Article in English | MEDLINE | ID: mdl-28832137

ABSTRACT

Under oxidative conditions, 1,4-dihydropyridines (DHPs) undergo a homolytic cleavage, forming exclusively a Csp3-centered radical that can engage in the C-H alkylation of heterocyclic bases and 1,4-quinones. DHPs are readily prepared from aldehydes, and considering that aldehydes normally require harsh reaction conditions to take part in such transformations, with mixtures of alkylated and acylated products often being obtained, this net decarbonylative alkylation approach becomes particularly useful. The present method takes place under mild reaction conditions and requires only persulfate as a stoichiometric oxidant, making the procedure suitable for the late-stage C-H alkylation of complex molecules. Notably, structurally complex pharmaceutical agents could be functionalized or prepared with this protocol, such as the antimalarial Atovaquone and antitheilerial Parvaquone, thus evidencing its applicability. Mechanistic studies revealed a likely radical chain process via the formation of a dearomatized intermediate, providing a deeper understanding of the factors governing the reactivity of these radical forebears.


Subject(s)
Dihydropyridines/chemistry , Heterocyclic Compounds/chemistry , Quinones/chemistry , Alkylating Agents/chemistry , Alkylation , Oxidation-Reduction
8.
ACS Catal ; 6(12): 8004-8008, 2016 Dec 02.
Article in English | MEDLINE | ID: mdl-27990318

ABSTRACT

A Ni/photoredox dual catalytic cross-coupling is disclosed in which a diverse range of (hetero)aryl bromides are used as electrophiles, with 1,4-dihydropyridines serving as precursors to Csp3-centered alkyl radical coupling partners. The reported method is characterized by its extremely mild reaction conditions, enabling access to underexplored cores.

9.
J Am Chem Soc ; 138(20): 6384-7, 2016 05 25.
Article in English | MEDLINE | ID: mdl-27145029

ABSTRACT

A Pd-catalyzed C(sp(3))-H functionalization/carbenoid insertion is described. The method allows for the rapid synthesis of bicyclic frameworks, generating all-carbon quaternary centers via multiple C-C bond formations in a straightforward manner.

10.
J Am Chem Soc ; 135(34): 12576-9, 2013 Aug 28.
Article in English | MEDLINE | ID: mdl-23927556

ABSTRACT

An Fe-catalyzed conversion of aldehydes to ketones via [1,2]-shift has been developed. This skeletal rearrangement shows a wide substrate scope and chemoselectivity profile while exhibiting an excellent [1,2]-aryl or [1,2]-alkyl shift selectivity that is easily switched by electronic effects.

11.
Org Lett ; 14(20): 5234-7, 2012 Oct 19.
Article in English | MEDLINE | ID: mdl-23030460

ABSTRACT

The first Pd-catalyzed intramolecular acylation of aryl chlorides via C-H bond functionalization is presented. The method allows for the synthesis of a variety of elusive benzocyclobutenones with a wide range of functional groups and substitution patterns. We demonstrate that a change in the ligand backbone dictates the selectivity pattern.

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