scholarly journals Pentanidium-Catalyzed Direct Assembly of Vicinal All-Carbon Quaternary Stereocenters through C(sp 3 )-C(sp 3 ) Bond Formation

CCS Chemistry ◽  
2021 ◽  
pp. 1-21
Author(s):  
Xu Ban ◽  
Yifan Fan ◽  
Tuan-Khoa Kha ◽  
Richmond Lee ◽  
Choon Wee Kee ◽  
...  
Keyword(s):  
Bond Formation ◽  
Direct Assembly ◽  
Quaternary Stereocenters

scholarly journals Pentanidium-Catalyzed Direct Assembly of Vicinal All-Carbon Quaternary Stereocenters through C(sp3)-C(sp3) Bond Formation

2021 ◽  
Author(s):  
Choon-Hong Tan ◽  
Xu Ban ◽  
Yifan Fan ◽  
Tuan-Khoa Kha ◽  
Richmond Lee ◽  
...  
Keyword(s):  
Bond Formation ◽  
Direct Assembly ◽  
Tertiary Carbon ◽  
Asymmetric Coupling ◽  
Catalytic Asymmetric ◽  
Quaternary Stereocenters ◽  
Straightforward Approach

Abstract The stereoselective construction of vicinal all-carbon quaternary stereocenters has long been a formidable synthetic challenge. Direct asymmetric coupling of a tertiary carbon nucleophile with a tertiary carbon electrophile is the most straightforward approach but it is sterically and energetically disfavored. Herein, we described a catalytic asymmetric substitution, where racemic tertiary bromides directly couple with racemic secondary or tertiary carbanion, creating a series of congested carbon (sp3)-carbon(sp3) bonds, including isolated all-carbon quaternary stereocenters, vicinal tertiary/all-carbon quaternary stereocenters and vicinal all-carbon quaternary stereocenters. This double stereoconvergent process, using pentanidium as catalyst, affords substituted products in good enantioselectivities and diastereoselectivities.

Vinylogy in nitronates: utilization of α-aryl conjugated nitroolefins as a nucleophile for a highly stereoselective aza-Henry reaction

2015 ◽  
Vol 51 (21) ◽  
pp. 4437-4439 ◽  
Author(s):  
Keigo Oyaizu ◽  
Daisuke Uraguchi ◽  
Takashi Ooi
Keyword(s):  
Bond Formation ◽  
Henry Reaction ◽  
Quaternary Stereocenters

Vinylogous nitronates generated from α,β-disubstituted nitroolefins undergo stereoselective bond formation with aldimines at the sterically encumbered α-position, establishing contiguous tertiary–quaternary stereocenters.

scholarly journals Tailoring Tryptophan Synthase TrpB for Selective Quaternary Carbon Bond Formation

2019 ◽  
Author(s):  
Markus Dick ◽  
Nicholas S. Sarai ◽  
Michael W. Martynowycz ◽  
Tamir Gonen ◽  
Frances H. Arnold
Keyword(s):  
Condensation Reaction ◽  
Bond Formation ◽  
Tryptophan Synthase ◽  
Indole Derivatives ◽  
Quaternary Carbon ◽  
Noncanonical Amino Acids ◽  
Carbon Bond ◽  
E Coli ◽  
Tertiary Carbon ◽  
Quaternary Stereocenters

<div><div><div><p>We previously engineered the tryptophan synthase beta-subunit (TrpB), which catalyzes the condensation reaction between L-serine and indole to form L-tryptophan, to synthesize a range of modified tryptophans from serine and indole derivatives. In this study, we used directed evolution to engineer TrpB to accept 3-substituted oxindoles and form C–C bonds leading to new quaternary stereocenters. At first, the TrpBs that could use 3-substituted oxindoles preferentially formed N–C bonds by attacking the oxindole N<sub>1 </sub>atom. We found, however, that protecting the nitrogen encouraged evolution towards C-alkylation, which persisted even when this protection was removed. After seven rounds of evolution leading to a 400-fold improvement in activity, variant <i>Pf</i><sub>quat</sub> efficiently alkylates 3-substituted oxindoles to selectively form new stereocenters at the γ-position of the amino acid products. The configuration of the new γ-stereocenter of one of the products was determined from the crystal structure obtained by microcrystal electron diffraction (MicroED). Substrates structurally related to 3-methyloxindole such as lactones and ketones can also be used by the enzyme for quaternary carbon bond formation, where the biocatalyst exhibits excellent regioselectivity for the tertiary carbon atom. Highly thermostable and expressed at > 500 mg/L <i>E. coli</i> culture, TrpB <i>Pf</i><sub>quat </sub>provides an efficient and environmentally-friendly platform for the preparation of noncanonical amino acids bearing quaternary carbons.</p></div></div></div>

scholarly journals Tailoring Tryptophan Synthase TrpB for Selective Quaternary Carbon Bond Formation

2019 ◽  
Author(s):  
Markus Dick ◽  
Nicholas S. Sarai ◽  
Michael W. Martynowycz ◽  
Tamir Gonen ◽  
Frances H. Arnold
Keyword(s):  
Condensation Reaction ◽  
Bond Formation ◽  
Tryptophan Synthase ◽  
Indole Derivatives ◽  
Quaternary Carbon ◽  
Noncanonical Amino Acids ◽  
Carbon Bond ◽  
E Coli ◽  
Tertiary Carbon ◽  
Quaternary Stereocenters

<div><div><div><p>We previously engineered the tryptophan synthase beta-subunit (TrpB), which catalyzes the condensation reaction between L-serine and indole to form L-tryptophan, to synthesize a range of modified tryptophans from serine and indole derivatives. In this study, we used directed evolution to engineer TrpB to accept 3-substituted oxindoles and form C–C bonds leading to new quaternary stereocenters. At first, the TrpBs that could use 3-substituted oxindoles preferentially formed N–C bonds by attacking the oxindole N<sub>1 </sub>atom. We found, however, that protecting the nitrogen encouraged evolution towards C-alkylation, which persisted even when this protection was removed. After seven rounds of evolution leading to a 400-fold improvement in activity, variant <i>Pf</i><sub>quat</sub> efficiently alkylates 3-substituted oxindoles to selectively form new stereocenters at the γ-position of the amino acid products. The configuration of the new γ-stereocenter of one of the products was determined from the crystal structure obtained by microcrystal electron diffraction (MicroED). Substrates structurally related to 3-methyloxindole such as lactones and ketones can also be used by the enzyme for quaternary carbon bond formation, where the biocatalyst exhibits excellent regioselectivity for the tertiary carbon atom. Highly thermostable and expressed at > 500 mg/L <i>E. coli</i> culture, TrpB <i>Pf</i><sub>quat </sub>provides an efficient and environmentally-friendly platform for the preparation of noncanonical amino acids bearing quaternary carbons.</p></div></div></div>

Stereodivergent Alkyne Hydrofluorination Using a Simple Practical Reagent

2020 ◽  
Author(s):  
Rui Guo ◽  
Xiaotian Qi ◽  
Hengye Xiang ◽  
Paul Geaneoates ◽  
Ruihan Wang ◽  
...  
Keyword(s):  
Bond Formation ◽  
Biologically Active ◽  
Dft Studies ◽  
Thermodynamic Control ◽  
Important Goal ◽  
Peptide Bonds ◽  
Metal Free ◽  
Vinyl Cation ◽  
E And Z Isomers ◽  
Vinyl Fluorides

Vinyl fluorides play an important role in drug development as they serve as bioisosteres for peptide bonds and are found in a range of biologically active molecules. The discovery of safe, general and practical procedures to prepare vinyl fluorides remains an important goal and challenge for synthetic chemistry. Here we introduce an inexpensive and easily-handled reagent and report simple, scalable, and metal-free protocols for the regioselective and stereodivergent hydrofluorination of alkynes to access both the E and Z isomers of vinyl fluorides. These conditions were suitable for a diverse collection of alkynes, including several highly-functionalized pharmaceutical derivatives. Mechanistic and DFT studies support C–F bond formation through a vinyl cation intermediate, with the (E)- and (Z)-hydrofluorination products forming under kinetic and thermodynamic control, respectively.<br>

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

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

<p>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 <i>ortho</i>-, distal <i>meta</i>- and <i>para</i>-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(<i>sp<sup>2</sup></i>)-H functionalization <i>via</i> reversible imine formation. By overruling facile proximal C-H bond activation by imine-<i>N</i> 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.</p>

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

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 <i>ortho</i>-arylbenzylamines, however, effective <i>ortho</i>-C–C bond formation from C–H bond activation of free primary and secondary benzylamines using Pd<sup>II</sup> remains an outstanding challenge. Presented herein is a new strategy for constructing <i>ortho</i>-arylated primary and secondary benzylamines mediated by carbon dioxide (CO<sub>2</sub>). The use of CO<sub>2</sub> 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.

Radical Capture at Ni(II) Complexes: C-C, C-N, and C-O Bond Formation

2019 ◽  
Author(s):  
Abolghasem (Gus) Bakhoda ◽  
Stefan Wiese ◽  
Christine Greene ◽  
Bryan C. Figula ◽  
Jeffery A. Bertke ◽  
...  
Keyword(s):  
Functional Groups ◽  
Bond Formation ◽  
Dft Studies ◽  
Bond Forming ◽  
Aryl Amines ◽  
Shed Light ◽  
Competing Pathways

<p>The dinuclear b-diketiminato Ni<sup>II</sup><i>tert</i>-butoxide {[Me<sub>3</sub>NN]Ni}<sub>2</sub>(<i>μ</i>-O<i><sup>t</sup></i>Bu)<sub>2 </sub>(<b>2</b>), synthesized from [Me<sub>3</sub>NN]Ni(2,4-lutidine) (<b>1</b>) and di-<i>tert</i>-butylperoxide, is a versatile precursor for the synthesis of a series of Ni<sup>II</sup>complexes [Me<sub>3</sub>NN]Ni-FG to illustrate C-C, C-N, and C-O bond formation at Ni<sup>II </sup>via radicals. {[Me<sub>3</sub>NN]Ni}<sub>2</sub>(<i>μ</i>-O<i><sup>t</sup></i>Bu)<sub>2 </sub>reacts with nitromethane, alkyl and aryl amines, acetophenone, benzamide, ammonia and phenols to deliver corresponding mono- or dinuclear [Me<sub>3</sub>NN]Ni-FG species (FG = O<sub>2</sub>NCH<sub>2</sub>, R-NH, ArNH, PhC(O)NH, PhC(O)CH<sub>2</sub>, NH<sub>2</sub>and OAr). Many of these Ni<sup>II </sup>complexes are capable of capturing the benzylic radical PhCH(•)CH<sub>3 </sub>to deliver corresponding PhCH(FG)CH<sub>3 </sub>products featuring C-C, C-N or C-O bonds. DFT studies shed light on the mechanism of these transformations and suggest two competing pathways that depend on the nature of the functional groups. These radical capture reactions at [Ni<sup>II</sup>]-FG complexes outline key C-C, C-N, and C-O bond forming steps and suggest new families of nickel radical relay catalysts.</p>

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