1994 Merck Frosst Award Lecture New strategies for the stereoselective synthesis of natural and unnatural products via organometallic reagents and catalysts

1995 ◽  
Vol 73 (8) ◽  
pp. 1251-1257 ◽  
Author(s):  
Mark Lautens ◽  
Yi Ren ◽  
Patrick Delanghe ◽  
Pauline Chiu ◽  
Shihong Ma ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Palladium Catalyst ◽  
Stereoselective Synthesis ◽  
Nickel Catalysts ◽  
X Ray Diffraction ◽  
Organometallic Reagents ◽  
Intramolecular Cycloaddition ◽  
X Ray ◽  
Acid Lactone ◽  
New Strategies

Samarium in the presence of diiodomethane selectively cyclopropanates an allenic alcohol to yield a methylenecyclopropane with modest to excellent diastereoselectivity. The effect of substituents at the carbinol carbon and the allenic carbon on the diastereoselectivity was investigated. A palladium catalyst was shown to promote the intramolecular cycloaddition of the methylenecyclopropane with an electron-deficient alkyne to yield a methylenecyclopentane. The reaction was stereospecific with retention of stereochemistry as proven by X-ray diffraction. Nickel catalysts accelerate the hydroalumination of oxabicyclo[3.2.1]alkenes, leading to bicyclic trialkylalanes. Upon treatment with a Lewis acid (diisobutylaluminum chloride), the trialkylalanes fragment to provide cycloheptenols. This reaction, followed by an enantioselective enzyme-catalyzed esterification, was used as a key step in a synthesis of the mevinic acid lactone. Keywords: methylenecyclopropane, palladium, stereocontrol, oxabicyclic, nickel.

An Intramolecular Boron Nitrogen Lewis Acid Base Pair on a Rigid Naphthyl Backbone

2012 ◽  
Vol 67 (6) ◽  
pp. 589-593 ◽  
Author(s):  
Daniel Winkelhaus ◽  
Beate Neumann ◽  
Norbert W. Mitzel
Keyword(s):  
Nmr Spectroscopy ◽  
Single Crystal ◽  
Lewis Acid ◽  
Elemental Analysis ◽  
Base Pair ◽  
Ring System ◽  
X Ray Diffraction ◽  
Acid Base ◽  
X Ray ◽  
Boron Nitrogen

The reaction of (C6F5)2BCl with 8-lithio-N,N-dimethyl-1-naphthylamine (1) afforded the fivemembered ring system 8-bis(pentafluorophenyl)boryl-N,N-dimethyl-1-naphthylamine (2) with an intramolecular dative B-N bond. The compound was characterised by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction.

Conformational study of the 3,6-dihydro-2H-1,4-oxazin-2-one fragment in 8-tert-butyl-7-methoxy-8-methyl-9-oxa-6-azaspiro[4.5]decane-2,10-dione stereoisomers

2017 ◽  
Vol 73 (7) ◽  
pp. 556-562
Author(s):  
Ewa Żesławska ◽  
Anna Jakubowska ◽  
Wojciech Nitek
Keyword(s):  
Amino Acids ◽  
Crystal Structures ◽  
Stereoselective Synthesis ◽  
Biologically Active ◽  
Asymmetric Unit ◽  
Conformational Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Natural Amino Acids ◽  
Heterocyclic Moiety

Unnatural cyclic α-amino acids play an important role in the search for biologically active compounds and macromolecules. Enantiomers of natural amino acids with a D configuration are not naturally encoded, but can be chemically synthesized. The crystal structures of two enantiomers obtained by a method of stereoselective synthesis, namely (5R,8S)-8-tert-butyl-7-methoxy-8-methyl-9-oxa-6-azaspiro[4.5]decane-2,10-dione, (1), and (5S,8R)-8-tert-butyl-7-methoxy-8-methyl-9-oxa-6-azaspiro[4.5]decane-2,10-dione, (2), both C14H21NO4, were determined by X-ray diffraction. Both enantiomers crystallize isostructurally in the space group P21, with one molecule in the asymmetric unit and with the same packing motif. The crystal structures are stabilized by C—H...O hydrogen bonds, resulting in the formation of chains along the [100] and [010] directions. The conformation of the 3,6-dihydro-2H-1,4-oxazin-2-one fragment was compared with other crystal structures possessing this heterocyclic moiety. The comparison showed that the title compounds are not exceptional among structures containing the 3,6-dihydro-2H-1,4-oxazin-2-one fragment. The planar moiety was more frequently observed in derivatives in which this fragment was not condensed with other rings.

Composition and structure of pyrophoric nickel catalysts according to X-ray diffraction data

2017 ◽  
Vol 91 (1) ◽  
pp. 30-35 ◽  
Author(s):  
T. Yu. Osadchaya ◽  
A. V. Afineevskii ◽  
D. A. Prozorov ◽  
S. P. Kochetkov ◽  
R. N. Rumyantsev ◽  
...  
Keyword(s):  
Diffraction Data ◽  
Nickel Catalysts ◽  
X Ray Diffraction ◽  
X Ray ◽  
Composition And Structure

Characterization of nickel catalysts by chemisorption techniques, x-ray diffraction and magnetic measurements

1989 ◽  
Vol 46 (2) ◽  
pp. 281-296 ◽  
Author(s):  
C. Hoang-Van ◽  
Y. Kachaya ◽  
S.J. Teichner ◽  
Y. Arnaud ◽  
J.A. Dalmon
Keyword(s):  
Magnetic Measurements ◽  
Nickel Catalysts ◽  
X Ray Diffraction ◽  
X Ray

2-Azabuta-1,3-diene-4-carbonitriles: stereoselective synthesis and nucleophilic substitution at the carbon–nitrogen double bond

1996 ◽  
Vol 74 (3) ◽  
pp. 287-294 ◽  
Author(s):  
Antonio Lorente ◽  
Marta Casillas ◽  
Pilar Gomez-Sal ◽  
Antonio Manzanero
Keyword(s):  
Double Bond ◽  
Nucleophilic Substitution ◽  
Key Words ◽  
Sodium Methoxide ◽  
Stereoselective Synthesis ◽  
X Ray Diffraction ◽  
Key Words 2 ◽  
X Ray ◽  
Nitrogen Double Bond

The synthesis of (E)-1-methoxy-2-azabuta-1,3-diene-4-carbonitriles was performed by methylation of N-alkenylamides 9 and 11. The Z isomers were obtained by treatment of (E)-1-methylthio-2-azabuta-1,3-diene-4,4-dicarbonitriles with sodium methoxide in methanol. We also describe the reactions of (E)-1-methylthio-2-azabuta-1,3-diene-4,4-dicarbonitriles with pyrrolidine, which afforded 1-(1-pyrrolidinyl) derivatives 20, 21, and 23. X-ray crystallographic analyses of 21 and 23 established the E stereochemistry of the C—N double bond. Key words: 2-azabuta-1,3-diene-4-carbonitriles: stereoselective synthesis, nucleophilic substitution and X-ray diffraction; N-alkenylamides: methylation.

scholarly journals Crystal structure of a zwitterionic azaallyl zirconiumamide complex bearing a Zr+-μ-CH3—B− moiety and one equivalent of n-hexane as a solvent

IUCrData ◽  
2018 ◽  
Vol 3 (5) ◽  
Author(s):  
Nils Frerichs ◽  
Christian Adler ◽  
Marc Schmidtmann ◽  
Rüdiger Beckhaus
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Lewis Acid ◽  
Tetrahedral Coordination ◽  
X Ray Diffraction ◽  
Coordination Environment ◽  
X Ray ◽  
Strong Lewis Acid ◽  
Distorted Tetrahedral Coordination

The zirconiumamide complex [(cyclohex-1-enyl)cyclohexylamido]bis(dicyclohexylamido)[methyltris(pentafluorophenyl)borato]zirconium(IV) hexane monosolvate, [Zr{N(C6H11)2}2{N(C6H11)(C6H9)}{BCH3(C6F5)3}]·C6H14, is zwitterionic and bears a Zr+—μ-CH3—B− moiety. The reaction of tris(dicyclohexylamido)methylzirconium with the strong Lewis acid tris(pentafluorophenyl)borane results in the formation of an azaallyl zirconium motif by the loss of H2 in one dicyclohexylamido ligand, as shown by single-crystal X-ray diffraction. The ZrIV cation is coordinated to the N atoms of two dicyclohexylamido ligands, the π-system of one azaallyl ligand, and to the μ-CH3—B unit, resulting in a distorted tetrahedral coordination environment. The Zr—N distance to the azaallyl ligand is elongated, whereas the Zr—C distance to this moiety is found to be shortened in comparison with those to the two Cy2N groups (Cy is C6H11).

Regio- and stereoselective synthesis of [1,3]thiazolo[3,2-b][1,2,4]triazol-7-ium salts via electrophilic heterocyclization of 3-S-propargylthio-4Н-1,2,4-triazoles and their antimicrobial activity

2017 ◽  
Vol 23 (2) ◽  
pp. 109-113 ◽  
Author(s):  
Mikhailo Slivka ◽  
Nataliya Korol ◽  
Valerij Pantyo ◽  
Vjacheslav Baumer ◽  
Vasil Lendel
Keyword(s):  
Antimicrobial Activity ◽  
Diffraction Analysis ◽  
Stereoselective Synthesis ◽  
Geometric Isomers ◽  
X Ray Diffraction ◽  
X Ray ◽  
H Nmr ◽  
Electrophilic Heterocyclization ◽  
Better Than ◽  
C Nmr

AbstractA procedure for the preparation of the title salts via regioselective halocyclization of 3-S-propargylthio-4Н-1,2,4-triazoles is reported. Stereoselectivity of electrophilic heterocyclization depends on the nature of the electrophilic reagent: bromination is better than iodobromination and iodination. The heterocyclization with tellurium tetrahalogenides leads to the formation of a mixture of geometric isomers of the salts. Their structure was confirmed by 1H NMR, 13C NMR, НМВС and single crystal X-ray diffraction analysis.

scholarly journals Synthesis and crystallographic characterization of [2,2-bis(η5-pentamethylcyclopentadienyl)-3,4-bis(trimethylsilyl)-2-zirconafuran-5-one-κO5]triisobutylaluminium

2018 ◽  
Vol 74 (4) ◽  
pp. 566-568
Author(s):  
Vladimir V. Burlakov ◽  
Vyacheslav S. Bogdanov ◽  
Perdita Arndt ◽  
Anke Spannenberg ◽  
Uwe Rosenthal ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Lewis Acid ◽  
X Ray Diffraction ◽  
X Ray

The crystal structure of the title zwitterionic zirconocene complex containing a furanone unit, [AlZr(C10H15)2(C4H9)3(C9H18O2Si2)], is reported. On reacting a zirconafuranone with two equivalents of HAl(i-Bu)2, disproportionation of the Lewis acid results in the formation of a triisobutylaluminium fragment, Al(i-Bu)3, which coordinates to the exocyclic carbonyl O atom of the zirconafuranone ring. Single-crystal X-ray diffraction reveals that the zirconafuranone ring remains intact with coordination of the aluminium to the exocyclic O atom. One of thei-butyl groups is disordered over two sets of sites, with an occupancy ratio of 0.731 (3):0.269 (3).

Sign in / Sign up

Export Citation Format

Share Document