Brandon L. Ashfeld

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Name: Ashfeld, Brandon

Organization: University of Notre Dame , USA

Department: Department of Chemistry and Biochemistry

Title: (PhD)

TOPICS

Organic Chemistry

Ionic Liquid

Chemicals
References

Rearrangement of an Intermediate Cyclopropyl Ketene in a RhII-Catalyzed Formal [4 + 1]-Cycloaddition Employing Vinyl Ketenes as 1,4-Dipoles and Donor–Acceptor Metallocarbenes

Co-reporter:Kevin X. Rodriguez, Nicolai Kaltwasser, Tiffany A. Toni, and Brandon L. Ashfeld

Organic Letters May 19, 2017 Volume 19(Issue 10) pp:

Publication Date(Web):April 28, 2017

DOI:10.1021/acs.orglett.7b00618

A RhII-catalyzed formal [4 + 1]-cycloaddition approach toward spirooxindole cyclopentenones is described. The diastereoselective cyclopropanation of vinyl ketenes with diazooxindoles as C1 synthons initiated a relatively mild formal [1,3]-migration of an intermediate cyclopropyl ketene to provide spirooxindoles in good to excellent yields (36–99%).

Phosphorus(III)-Mediated Stereoconvergent Formal [4+1]-Cycloannulation of 1,2-Dicarbonyls and o-Quinone Methides: A Multicomponent Assembly of 2,3-Dihydrobenzofurans

Co-reporter:Kevin X. Rodriguez, Justin D. Vail, and Brandon L. Ashfeld

Organic Letters 2016 Volume 18(Issue 18) pp:4514-4517

Publication Date(Web):September 7, 2016

DOI:10.1021/acs.orglett.6b02122

A phosphorus(III)-mediated formal [4+1]-cycloaddition of 1,2-dicarbonyls and o-quinone methides to provide 2,3-dihydrobenzofurans is described. By exploiting the carbene-like nature of dioxyphospholenes, dihydrobenzofurans bearing a quaternary center at C2 are obtained in 30–92% yield with diastereoselectivities up to ≥20:1. This study highlights the subtle steric interactions involved in the [4+1]-cycloannulation and the impact they have on yield and stereoselectivity in dihydrobenzofuran formation.

Stereochemical implications in the synthesis of 3,3′-spirocyclopropyl oxindoles from β-aryl/alkyl-substituted alkylidene oxindoles

Co-reporter:Erin E. Wilson, Kevin X. Rodriguez, Brandon L. Ashfeld

Tetrahedron 2015 Volume 71(Issue 35) pp:5765-5775

Publication Date(Web):2 September 2015

DOI:10.1016/j.tet.2015.06.004

3,3′-Spirocyclopropane oxindoles were synthesized in good to excellent yield and diastereoselectivity employing a Kukhtin–Ramirez reaction between readily accessible E-alkylidene oxindoles, commercially available P(NMe2)3, and α-keto esters. The stereoselectivity in the cyclopropanation event can be traced to the starting alkylidene geometry and the propensity of the exocyclic alkene to undergo isomerization in the presence of an electron rich phosphine.

An umpolung approach toward N-aryl nitrone construction: a phosphine-mediated addition of 1,2-dicarbonyls to nitroso electrophiles

Co-reporter:Aditi P. Chavannavar, Allen G. Oliver and Brandon L. Ashfeld

Chemical Communications 2014 vol. 50(Issue 74) pp:10853-10856

Publication Date(Web):24 Jul 2014

DOI:10.1039/C4CC05044D

An umpolung approach toward nitrone construction utilizing a phosphine-mediated addition of 1,2-dicarbonyls to nitroso compounds is reported. The reaction exhibits a high degree of chemoselectivity and provides direct access to isoxazolidines, imines, and trisubstituted alkenes.

Titanocene-catalyzed metallation of propargylic acetates in homopropargyl alcohol synthesis

Co-reporter:Jennifer L. Meloche, Peter T. Vednor, Joseph B. Gianino, Allen G. Oliver, Brandon L. Ashfeld

Tetrahedron Letters 2014 Volume 55(Issue 36) pp:5025-5028

Publication Date(Web):3 September 2014

DOI:10.1016/j.tetlet.2014.07.029

The titanium-catalyzed metallation and subsequent carbonyl addition of propargylic acetates enable the direct formation of homopropargylic alcohols in good yields. The corresponding products were obtained as single regioisomers without the corresponding allene adducts observed.

Redox and Lewis Acid Relay Catalysis: A Titanocene/Zinc Catalytic Platform in the Development of Multicomponent Coupling Reactions

Co-reporter:Joseph B. Gianino, Catherine A. Campos, Antonio J. Lepore, David M. Pinkerton, and Brandon L. Ashfeld

The Journal of Organic Chemistry 2014 Volume 79(Issue 24) pp:12083-12095

Publication Date(Web):October 3, 2014

DOI:10.1021/jo501890z

A titanocene-catalyzed multicomponent coupling is described herein. Using catalytic titanocene, phosphine, and zinc dust, zinc acetylides can be generated from the corresponding iodoalkynes to affect sequential nucleophilic additions to aromatic aldehydes. The intermediate propargylic alkoxides are trapped in situ with acetic anhydride, which are susceptible to a second nucleophilic displacement upon treatment with a variety of electron-rich species, including acetylides, allyl silanes, electron-rich aromatics, silyl enol ethers, and silyl ketene acetals. Additionally, employing cyclopropane carboxaldehydes led to ring-opened products resulting from iodine incorporation. Taken together, these results form the basis for a new mode of three-component coupling reactions, which allows for rapid access to value added products in a single synthetic operation.

Site specific carboxylation of abnormal anionic N-heterocyclic dicarbenes with CO2

Co-reporter:Monika Vogt, Chao Wu, Allen G. Oliver, Christopher J. Meyer, William F. Schneider and Brandon L. Ashfeld

Chemical Communications 2013 vol. 49(Issue 98) pp:11527-11529

Publication Date(Web):31 Oct 2013

DOI:10.1039/C3CC46555A

Herein, we report experimental and computational results for the carboxylation of abnormal anionic N-heterocyclic dicarbenes (NHDCs) with CO2. Under ambient dosing conditions, carbonyl addition occurs selectively at C4 without a second carboxylation event occurring at the C2 carbene center.

Bifunctional Titanocene Catalysis in Multicomponent Couplings: A Convergent Assembly of β-Alkynyl Ketones

Co-reporter:Catherine A. Campos, Joseph B. Gianino, and Brandon L. Ashfeld

Organic Letters 2013 Volume 15(Issue 11) pp:2656-2659

Publication Date(Web):May 14, 2013

DOI:10.1021/ol400943a

Herein is described a titanium-catalyzed three-component coupling to assemble β-alkynyl ketones in a single operation. Treatment of an aryl aldehyde with an acetylide and silyl enol ether in the presence of a bifunctional titanocene catalyst enables the highly convergent assembly of β-alkynyl ketones in good to excellent yields.

Relay Redox and Lewis Acid Catalysis in the Titanocene- Catalyzed Multicomponent Assembly of 1,5-Enynes

Co-reporter:Antonio J. Lepore;David M. Pinkerton ;Bron L. Ashfeld

Advanced Synthesis & Catalysis 2013 Volume 355( Issue 8) pp:1500-1504

Publication Date(Web):

DOI:10.1002/adsc.201300359

Abstract

Herein we describe a direct, multicomponent assembly of 1,5-enynes. The titanocene-catalyzed coupling of an aryl aldehyde, iodoalkyne, and allylsilane enables the convergent and rapid synthesis of this versatile architectural motif in good to excellent yields.

Cooperative Titanocene and Phosphine Catalysis: Accelerated C–X Activation for the Generation of Reactive Organometallics

Co-reporter:Lauren M. Fleury, Andrew D. Kosal, James T. Masters, and Brandon L. Ashfeld

The Journal of Organic Chemistry 2013 Volume 78(Issue 2) pp:253-269

Publication Date(Web):October 24, 2012

DOI:10.1021/jo301726v

The study presented herein describes a reductive transmetalation approach toward the generation of Grignard and organozinc reagents mediated by a titanocene catalyst. This method enables the metalation of functionalized substrates without loss of functional group compatibility. Allyl zinc reagents and allyl, vinyl, and alkyl Grignard reagents were generated in situ and used in the addition to carbonyl substrates to provide the corresponding carbinols in yields up to 99%. It was discovered that phosphine ligands effectively accelerate the reductive transmetalation event to enable the metalation of C–X bonds at temperatures as low as −40 °C. Performing the reactions in the presence of chiral diamines and amino alcohols led to the enantioselective allylation of aldehydes.

Amine-Free Approach toward N-Toluenesulfonyl Amidine Construction: A Phosphite-Mediated Beckmann-Like Coupling of Oximes and p-Toluenesulfonyl Azide

Co-reporter:Lauren M. Fleury;Erin E. Wilson;Monika Vogt;Tiffany J. Fan;Allen G. Oliver ;Dr. Bron L. Ashfeld

Angewandte Chemie 2013 Volume 125( Issue 44) pp:11803-11807

Publication Date(Web):

DOI:10.1002/ange.201305141

Amine-Free Approach toward N-Toluenesulfonyl Amidine Construction: A Phosphite-Mediated Beckmann-Like Coupling of Oximes and p-Toluenesulfonyl Azide

Co-reporter:Lauren M. Fleury;Erin E. Wilson;Monika Vogt;Tiffany J. Fan;Allen G. Oliver ;Dr. Bron L. Ashfeld

Angewandte Chemie International Edition 2013 Volume 52( Issue 44) pp:11589-11593

Publication Date(Web):

DOI:10.1002/anie.201305141

Design, synthesis, and evaluation of curcumin-derived arylheptanoids for glioblastoma and neuroblastoma cytotoxicity

Co-reporter:Catherine A. Campos, Joseph B. Gianino, Barbara J. Bailey, Mary E. Baluyut, Constanze Wiek, Helmut Hanenberg, Harlan E. Shannon, Karen E. Pollok, Brandon L. Ashfeld

Bioorganic & Medicinal Chemistry Letters 2013 23(24) pp: 6874-6878

Publication Date(Web):

DOI:10.1016/j.bmcl.2013.09.095

Solid-State Covalent Capture of CO2 by Using N-Heterocyclic Carbenes

Co-reporter:Dr. Monika Vogt;Joshua E. Bennett;Yong Huang;Dr. Chao Wu; William F. Schneider; Joan F. Brennecke; Bron L. Ashfeld

Chemistry - A European Journal 2013 Volume 19( Issue 34) pp:11134-11138

Publication Date(Web):

DOI:10.1002/chem.201302013

Titanocene-Catalyzed Multicomponent Coupling Approach to Diarylethynyl Methanes

Co-reporter:Joseph B. Gianino

Journal of the American Chemical Society 2012 Volume 134(Issue 44) pp:18217-18220

Publication Date(Web):October 21, 2012

DOI:10.1021/ja308891e

A titanocene-catalyzed multicomponent coupling to provide diarylethynyl methanes is described. By combining the multifunctionality of Cp2TiCl2 with the traceless dielectrophilicity of aryl aldehydes, all-carbon tertiary centers are obtained in 55–99% yield.

Positional chemoselectivity in the Zn(II)-mediated removal of phenol protecting groups

Co-reporter:Lauren M. Fleury, Joseph B. Gianino, Brandon L. Ashfeld

Tetrahedron Letters 2012 Volume 53(Issue 40) pp:5376-5379

Publication Date(Web):3 October 2012

DOI:10.1016/j.tetlet.2012.07.103

A protocol was developed for the chemoselective ortho-deprotection of polyphenolic substrates using readily available ZnIIX2 salts. This procedure provides exceptional positional selectivity for the deprotection of phenols that reside adjacent to directing carbonyl functionality in the presence of similar protecting groups at the meta and para positions. Good to excellent yields of the desired free phenols were obtained (⩽96%), and a wide assortment of protecting groups was readily removed under the reaction conditions.

Phosphine-Based Redox Catalysis in the Direct Traceless Staudinger Ligation of Carboxylic Acids and Azides

Co-reporter:Andrew D. Kosal;Erin E. Wilson;Dr. Bron L. Ashfeld

Angewandte Chemie International Edition 2012 Volume 51( Issue 48) pp:12036-12040

Publication Date(Web):

DOI:10.1002/anie.201206533

Phosphine-Based Redox Catalysis in the Direct Traceless Staudinger Ligation of Carboxylic Acids and Azides

Co-reporter:Andrew D. Kosal;Erin E. Wilson;Dr. Bron L. Ashfeld

Angewandte Chemie 2012 Volume 124( Issue 48) pp:12202-12206

Publication Date(Web):

DOI:10.1002/ange.201206533

Direct Acyl Substitution of Carboxylic Acids: A Chemoselective O- to N-Acyl Migration in the Traceless Staudinger Ligation

Co-reporter:Andrew D. Kosal;Erin E. Wilson ;Dr. Bron L. Ashfeld

Chemistry - A European Journal 2012 Volume 18( Issue 45) pp:14444-14453

Publication Date(Web):

DOI:10.1002/chem.201201773

Abstract

A chlorophosphite-modified, Staudinger-like acylation of azides involving a highly chemoselective, direct nucleophilic acyl substitution of carboxylic acids is described. The reaction provides the corresponding amides with analytical purity in 32–97 % yield after a simple aqueous workup without the need for a pre-activation step. The use of chlorophosphites as dual carboxylic acid–azide activating agents enables the formation of acyl CN bonds in the presence of a wide range of nucleophilic and electrophilic functional groups, including amines, alcohols, amides, aldehydes, and ketones. The coupling of carboxylic acids and azides for the formation of alkyl amides, sulfonyl amides, lactams, and dipeptides is described.

Synthesis of Phosphine-Ligated Zinc Acetylide Dimers: Enhanced Reactivity in Carbonyl Additions

Co-reporter:Erin E. Wilson, Allen G. Oliver, Russell P. Hughes, and Brandon L. Ashfeld

Organometallics 2011 Volume 30(Issue 19) pp:5214-5221

Publication Date(Web):September 8, 2011

DOI:10.1021/om200581f

Phosphine-ligated dinuclear zinc acetylides effectively promote the alkynylation of carbonyl derivatives. Good to excellent yields (46–91%) of the corresponding propargylic alcohols were obtained from a wide range of substrates. Crystallographic evidence for a phosphine–zinc–acetylide dimer was obtained with bonding energies obtained by DFT calculations. Phosphine ligation in the carbon–carbon bond-forming event is further corroborated by the synthesis of an enantioenriched propargylic alcohol through the addition of chiral phosphines.

Titanocene-Catalyzed Conjugate Reduction of α,β-Unsaturated Carbonyl Derivatives

Co-reporter:Andrew D. Kosal and Brandon L. Ashfeld

Organic Letters 2010 Volume 12(Issue 1) pp:44-47

Publication Date(Web):December 7, 2009

DOI:10.1021/ol9024315

A titanocene-catalyzed conjugate reduction of α,β-unsaturated carbonyl derivatives has been developed. A series of carbonyl compounds including aldehydes, ketones, esters, and amides proved viable in the reduction process providing an efficient, chemoselective method for the catalytic reduction of unsaturated carbonyl derivatives.

Generation of allyl Grignard reagents via titanocene-catalyzed activation of allyl halides

Co-reporter:Lauren M. Fleury, Brandon L. Ashfeld

Tetrahedron Letters 2010 Volume 51(Issue 18) pp:2427-2430

Publication Date(Web):5 May 2010

DOI:10.1016/j.tetlet.2010.02.144

A protocol for the generation of allyl Grignard reagents via the catalytic activation of allyl halides is described herein. Subsequent nucleophilic addition to carbonyl derivatives provided the desired homo allylic alcohols in excellent yields (84–99%). Evidence suggests that titanocene dichloride catalyzes the formation of an allyl Grignard species which reacts solely with the carbonyl electrophile as evidenced by the complete absence of Würtz coupling. This methodology will have wide-ranging applicability in the generation of highly reactive organometallic reagents.

Organozinc Generation via the Titanium-Catalyzed Activation of Alkyl Halides

Co-reporter:Lauren M. Fleury and Brandon L. Ashfeld

Organic Letters 2009 Volume 11(Issue 24) pp:5670-5673

Publication Date(Web):November 19, 2009

DOI:10.1021/ol902374v

A protocol for the generation of organozinc reagents via catalytic activation of alkyl halides is described herein. Subsequent nucleophilic addition to carbonyl derivatives provided the desired products in good to excellent yields (76−99%). Evidence suggests that titanocene dichloride catalyzes the formation of an organozinc species. This discovery will have wide ranging applicability in the generation of highly reactive organometallic reagents.

An umpolung approach toward N-aryl nitrone construction: a phosphine-mediated addition of 1,2-dicarbonyls to nitroso electrophiles

Co-reporter:Aditi P. Chavannavar, Allen G. Oliver and Brandon L. Ashfeld

Chemical Communications 2014 - vol. 50(Issue 74) pp:NaN10856-10856

Publication Date(Web):2014/07/24

DOI:10.1039/C4CC05044D

Site specific carboxylation of abnormal anionic N-heterocyclic dicarbenes with CO2

Co-reporter:Monika Vogt, Chao Wu, Allen G. Oliver, Christopher J. Meyer, William F. Schneider and Brandon L. Ashfeld

Chemical Communications 2013 - vol. 49(Issue 98) pp:NaN11529-11529

Publication Date(Web):2013/10/31

DOI:10.1039/C3CC46555A