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Michael J Krische - One of the best experts on this subject based on the ideXlab platform.
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ruthenium catalyzed diastereo and enantioselective coupling of propargyl ethers with alcohols siloxy Crotylation via hydride shift enabled conversion of alkynes to π allyls
Journal of the American Chemical Society, 2015Co-Authors: Tao Liang, Wandi Zhang, Teyu Chen, Khoa D Nguyen, Michael J KrischeAbstract:The first enantioselective carbonyl Crotylations through direct use of alkynes as chiral allylmetal equivalents are described. Chiral ruthenium(II) complexes modified by Josiphos (SL-J009-1) catalyze the C-C coupling of TIPS-protected propargyl ether 1a with primary alcohols 2a-2o to form products of carbonyl siloxy-Crotylation 3a-3o, which upon silyl deprotection-reduction deliver 1,4-diols 5a-5o with excellent control of regio-, anti-diastereo-, and enantioselectivity. Structurally related propargyl ethers 1b and 1c bearing ethyl- and phenyl-substituents engage in diastereo- and enantioselective coupling, as illustrated in the formation of adducts 5p and 5q, respectively. Selective mono-tosylation of diols 5a, 5c, 5e, 5f, 5k, and 5m is accompanied by spontaneous cyclization to deliver the trans-2,3-disubstituted furans 6a, 6c, 6e, 6f, 6k, and 6m, respectively. Primary alcohols 2a, 2l, and 2p were converted to the siloxy-Crotylation products 3a, 3l, and 3p, which upon silyl deprotection-lactol oxidation were transformed to the trans-4,5-disubstituted γ-butyrolactones 7a, 7l, and 7p. The formation of 7p represents a total synthesis of (+)-trans-whisky lactone. Unlike closely related ruthenium catalyzed alkyne-alcohol C-C couplings, deuterium labeling studies provide clear evidence of a novel 1,2-hydride shift mechanism that converts metal-bound alkynes to π-allyls in the absence of intervening allenes.
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Formal Synthesis of Premisakinolide A and C(19)-C(32) of Swinholide A via Site-Selective C-H Allylation and Crotylation of Unprotected Diols.
Organic Letters, 2015Co-Authors: Inji Shin, Michael J KrischeAbstract:Using stereo- and site-selective C–H allylation and Crotylation of unprotected diols, an intermediate in the synthesis of premisakinolide A (bistheonellic acid B) that was previously made in 16–27 (LLS) steps is now prepared in only nine steps. This fragment also represents a synthesis of C(19)–C(32) of the actin-binding macrodiolide swinholide A.
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Direct Generation of Triketide Stereopolyads via Merged Redox-Construction Events: Total Synthesis of (+)-Zincophorin Methyl Ester
Journal of the American Chemical Society, 2015Co-Authors: Zachary A. Kasun, Xin Gao, Radoslaw M. Lipinski, Michael J KrischeAbstract:(+)-Zincophorin methyl ester is prepared in 13 steps (longest linear sequence). A bidirectional redox-triggered double anti-Crotylation of 2-methyl-1,3-propane diol directly assembles the triketide stereopolyad spanning C4–C12, significantly enhancing step economy and enabling construction of (+)-zincophorin methyl ester in nearly half the steps previously required.
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Formal Synthesis of Premisakinolide A and C(19)–C(32) of Swinholide A via Site-Selective C–H Allylation and Crotylation of Unprotected Diols
2015Co-Authors: Inji Shin, Michael J KrischeAbstract:Using stereo- and site-selective C–H allylation and Crotylation of unprotected diols, an intermediate in the synthesis of premisakinolide A (bistheonellic acid B) that was previously made in 16–27 (LLS) steps is now prepared in only nine steps. This fragment also represents a synthesis of C(19)–C(32) of the actin-binding macrodiolide swinholide A
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Direct Generation of Triketide Stereopolyads via Merged Redox-Construction Events: Total Synthesis of (+)-Zincophorin Methyl Ester
2015Co-Authors: Zachary A. Kasun, Xin Gao, Radoslaw M. Lipinski, Michael J KrischeAbstract:(+)-Zincophorin methyl ester is prepared in 13 steps (longest linear sequence). A bidirectional redox-triggered double anti-Crotylation of 2-methyl-1,3-propane diol directly assembles the triketide stereopolyad spanning C4–C12, significantly enhancing step economy and enabling construction of (+)-zincophorin methyl ester in nearly half the steps previously required
Patrick J. Guiry - One of the best experts on this subject based on the ideXlab platform.
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application of tridentate bis oxazoline ligands in catalytic asymmetric nozaki hiyama allylation and Crotylation an example of high enantioselection with a non symmetric bis oxazoline ligand
Advanced Synthesis & Catalysis, 2006Co-Authors: Helen A. Mcmanus, Pier Giorgio Cozzi, Patrick J. GuiryAbstract:A series of both symmetric and non-symmetric bis(oxazoline) ligands was applied in the Nozaki–Hiyama allylation and Crotylation of benzaldehyde. It was found that both the magnitude and sense of the asymmetric induction depended strongly on the nature and combination of the oxazoline substituents. For both reactions, the non-symmetric tert-butyl/benzyl-substituted ligand proved to be the optimal ligand and was applied successfully in the allylation and Crotylation of a range of aryl and aliphatic aldehydes. The enantioselectivities obtained in allylation were up to 91% ee and in Crotylation up to 92% with typical syn:anti ratios of up to 80 : 20.
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Application of Tridentate Bis(oxazoline) Ligands in Catalytic Asymmetric Nozaki–Hiyama Allylation and Crotylation: An Example of High Enantioselection with a Non‐Symmetric Bis(oxazoline) Ligand
Advanced Synthesis & Catalysis, 2006Co-Authors: Helen A. Mcmanus, Pier Giorgio Cozzi, Patrick J. GuiryAbstract:A series of both symmetric and non-symmetric bis(oxazoline) ligands was applied in the Nozaki–Hiyama allylation and Crotylation of benzaldehyde. It was found that both the magnitude and sense of the asymmetric induction depended strongly on the nature and combination of the oxazoline substituents. For both reactions, the non-symmetric tert-butyl/benzyl-substituted ligand proved to be the optimal ligand and was applied successfully in the allylation and Crotylation of a range of aryl and aliphatic aldehydes. The enantioselectivities obtained in allylation were up to 91% ee and in Crotylation up to 92% with typical syn:anti ratios of up to 80 : 20.
Helen A. Mcmanus - One of the best experts on this subject based on the ideXlab platform.
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application of tridentate bis oxazoline ligands in catalytic asymmetric nozaki hiyama allylation and Crotylation an example of high enantioselection with a non symmetric bis oxazoline ligand
Advanced Synthesis & Catalysis, 2006Co-Authors: Helen A. Mcmanus, Pier Giorgio Cozzi, Patrick J. GuiryAbstract:A series of both symmetric and non-symmetric bis(oxazoline) ligands was applied in the Nozaki–Hiyama allylation and Crotylation of benzaldehyde. It was found that both the magnitude and sense of the asymmetric induction depended strongly on the nature and combination of the oxazoline substituents. For both reactions, the non-symmetric tert-butyl/benzyl-substituted ligand proved to be the optimal ligand and was applied successfully in the allylation and Crotylation of a range of aryl and aliphatic aldehydes. The enantioselectivities obtained in allylation were up to 91% ee and in Crotylation up to 92% with typical syn:anti ratios of up to 80 : 20.
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Application of Tridentate Bis(oxazoline) Ligands in Catalytic Asymmetric Nozaki–Hiyama Allylation and Crotylation: An Example of High Enantioselection with a Non‐Symmetric Bis(oxazoline) Ligand
Advanced Synthesis & Catalysis, 2006Co-Authors: Helen A. Mcmanus, Pier Giorgio Cozzi, Patrick J. GuiryAbstract:A series of both symmetric and non-symmetric bis(oxazoline) ligands was applied in the Nozaki–Hiyama allylation and Crotylation of benzaldehyde. It was found that both the magnitude and sense of the asymmetric induction depended strongly on the nature and combination of the oxazoline substituents. For both reactions, the non-symmetric tert-butyl/benzyl-substituted ligand proved to be the optimal ligand and was applied successfully in the allylation and Crotylation of a range of aryl and aliphatic aldehydes. The enantioselectivities obtained in allylation were up to 91% ee and in Crotylation up to 92% with typical syn:anti ratios of up to 80 : 20.
James S. Panek - One of the best experts on this subject based on the ideXlab platform.
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[4 + 2]-Cycloaddition and 1,4-Addition of ortho-Quinone Methides by a Chiral Crotyl Silane
Organic letters, 2018Co-Authors: Christopher R. Wong, Gerald Hummel, Yongqi Cai, Scott E. Schaus, James S. PanekAbstract:Anhydrous FeCl3 in the presence of 2,6-lutidine promotes the substrate-controlled enantioselective [4 + 2]-cycloaddition and Crotylation reaction between an enantioenriched (S,E)-crotyl silane and in situ generated ortho-quinone methides (oQMs). The reaction produces both the chiral chroman and Crotylation products in a ratio reflective of the electronic nature of the parent oQM with overall combined yields up to 96%. A ring-opening and elimination sequence was subsequently developed to provide direct access to the Crotylation products, containing two contiguous tertiary carbon stereocenters, in good yields and enantioselectivities.
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vinylogous aldol products from chiral crotylsilanes obtained by enantioselective rh ii and cu i carbenoid si h insertion
ChemInform, 2010Co-Authors: Yu Chen, James S. PanekAbstract:Chiral homoallylic ethers, bearing a α,β-unsaturated ester or silyl ether moiety, are prepared with moderate to high syn-selectivity via the Crotylation reaction of chiral silanes, aldehydes and trimethylalkoxysilanes.
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vinylogous aldol products from chiral crotylsilanes obtained by enantioselective rh ii and cu i carbenoid si h insertion
Organic Letters, 2010Co-Authors: Yu Chen, James S. PanekAbstract:Enantioenriched homoallylic ethers containing a α,β-unsaturated ester (syn-vinylogous aldol products) were directly accessed by Lewis acid catalyzed Crotylation utilizing chiral silane 2. The reagents were prepared by enantioselective Si−H insertion to an α-diazovinylacetates using Davies’ Rh2(DOSP)4 catalyst or chiral Cu(I) Schiff base complex.
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Preparation of Alkylidene Indane and Related Scaffolds and Their Further Elaboration to Novel Chemotypes
Organic letters, 2007Co-Authors: Sarathy Kesavan, James S. Panek, John A. PorcoAbstract:Alkylidene indane and ring-expanded scaffolds have been prepared using an enantioselective Crotylation/Heck cyclization sequence. Further diversification using consecutive cyclopropanation-Cope rearrangement affords novel chemotypes including spiroindane frameworks.
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Total synthesis of herboxidiene/GEX 1A.
Organic letters, 2007Co-Authors: Yun Zhang, James S. PanekAbstract:A convergent enantioselective synthesis of herboxidiene/GEX 1A (1) is described that features a double stereodifferentiating Crotylation, [4 + 2] annulation, and a silicon-based sp2−sp2 cross-coupling to assemble the conjugated diene.
Angshuman Chattopadhyay - One of the best experts on this subject based on the ideXlab platform.
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A practical procedure of low valent tin mediated Barbier allylation of aldehydes in wet solvent
Tetrahedron Letters, 2013Co-Authors: Conxin Vilanova, María Sánchez-peris, Steven Roldán, Bhaskar Dhotare, Miguel Carda, Angshuman ChattopadhyayAbstract:Abstract Use of aluminium as the reducing metal in spontaneous bimetal redox reaction has been elegantly exploited for allylation/Crotylation of aldehydes in wet solvent. Here, low valent tin was prepared in situ by reduction of SnCl 2 ·2H 2 O with aluminium in THF/water. The resulting low valent tin acted as an efficient mediator for allylation and Crotylation of aldehydes ( 3a – q ) producing the corresponding homoallylic alcohols. The efficacy of this procedure was due to its operational simplicity, practical viability, inexpensiveness, good yields of the products and short reaction time.
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A Novel Asymmetric Synthesis of the Core Octadienoic Acid Unit of Cryptophycins from (R)-2,3-O-Cyclohexylideneglyceraldehyde
Synthesis, 2011Co-Authors: Dibakar Goswami, Anubha Sharma, Angshuman Chattopadhyay, Payel Sur, Subrata ChattopadhyayAbstract:A facile asymmetric synthesis of the octadienoic acid unit of cryptophycins was developed starting from (R)-2,3-O-cyclo-hexylideneglyceraldehyde. The key steps of the synthesis are the stereocontrolled generation of the required asymmetric centers through (i) a gallium-mediated highly diastereoselective Crotylation of the glyceraldehyde in [bmim][Br], (ii) a stereoselective allylation with allyltributylstannane, and (iii) an enantioselective Grignard addition to an α-oxygenated aldehyde.
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Crotylation of r 2 3 o cyclohexylideneglyceraldehyde a simple synthesis of trans oak lactone
Tetrahedron Letters, 2010Co-Authors: Angshuman Chattopadhyay, Dibakar Goswami, Bhaskar DhotareAbstract:Abstract Crotylations of ( R )-2,3-cyclohexylideneglyceraldehyde ( 1 ) were utilized in a simple synthesis of trans -oak lactone ( I ), a representative example of chiral β,γ-disubstituted-γ-butyrolactones. In this endeavor, Crotylations of 1 in THF mediated with four low valent metals were studied. All these reactions took place efficiently producing 2 in good yields but with varied stereoselectivities. Each reaction produced the corresponding secondary alcohol adduct 2b and 2c predominantly with diastereoisomer 2a only in trace amounts. Among these four reactions, only Sn-mediated addition yielded 2b as the major products. Later, 2c was converted into 2d through oxidation–reduction. Finally, 2c was transformed into trans -oak lactone I in a few steps. Following this route, 2a , 2b , and 2d would produce other stereoisomers of oak lactone.
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Crotylation of (R)-2,3-O-cyclohexylideneglyceraldehyde: a simple synthesis of (+)-trans-oak lactone
Tetrahedron Letters, 2010Co-Authors: Angshuman Chattopadhyay, Dibakar Goswami, Bhaskar DhotareAbstract:Abstract Crotylations of ( R )-2,3-cyclohexylideneglyceraldehyde ( 1 ) were utilized in a simple synthesis of trans -oak lactone ( I ), a representative example of chiral β,γ-disubstituted-γ-butyrolactones. In this endeavor, Crotylations of 1 in THF mediated with four low valent metals were studied. All these reactions took place efficiently producing 2 in good yields but with varied stereoselectivities. Each reaction produced the corresponding secondary alcohol adduct 2b and 2c predominantly with diastereoisomer 2a only in trace amounts. Among these four reactions, only Sn-mediated addition yielded 2b as the major products. Later, 2c was converted into 2d through oxidation–reduction. Finally, 2c was transformed into trans -oak lactone I in a few steps. Following this route, 2a , 2b , and 2d would produce other stereoisomers of oak lactone.
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Metal-dependent modulation of diastereoselectivity in the Barbier-type Crotylation of (R)-cyclohexylideneglyceraldehyde
Tetrahedron: Asymmetry, 2009Co-Authors: Dibakar Goswami, Angshuman Chattopadhyay, Subrata ChattopadhyayAbstract:The diastereoselectivity of the Barbier-type Crotylation of (R)-cyclohexylideneglyceraldehyde could be tuned by changing the metal atom and solvent. The Ga-mediated reaction in [bmim][Br] produced the best diastereoselectivity, furnishing the all-anti product in good yield.