1,721,385 research outputs found
Chiral Aminophosphines as Catalysts for Enantioselective Double-Michael Indoline Syntheses
No full textThe bisphosphine-catalyzed double-Michael addition of dinucleophiles to electron-deficient acetylenes is an efficient process for the synthesis of many nitrogen-containing heterocycles. Because the resulting heterocycles contain at least one stereogenic center, this double-Michael reaction would be even more useful if an asymmetric variant of the reaction were to be developed. Aminophosphines can also facilitate the double-Michael reaction and chiral amines are more readily available in Nature and synthetically; therefore, in this study we prepared several new chiral aminophosphines. When employed in the asymmetric double-Michael reaction between <em>ortho</em>-tosylamidophenyl malonate and 3-butyn-2-one, the chiral aminophosphines produced indolines in excellent yields with moderate asymmetric induction
Synthesis of 4-Imidazolidinones from Diamides and Ethynyl Benzio- doxolones vis Double Michael Addition: Ethynyl Benziodoxolones as Electrophilic Ynol Synthons
No full textThe moiety of 4-imidazolidinone is an important structural motif in organic synthesis and medicinal chemistry. We achieved the efficient synthesis of 4-imidazolidinones from a variety of diamides by double Michael addition, a novel reaction mode for hypervalent alkynyl iodine compounds, and a formal reductive elimination sequence using in situ-generated EBX from TMS-EBX or EBX-MeCN. The highly reactive EBX enabled chemoselective intermolecular N- alkenylation of the sulfonamide moiety and intramolecular cyclization of the amide moiety under mild basic conditions. The reaction diastereoselectively gave cis-2,5-disubstituted 4-imidazolidinones from amino acid-derived diamides. Furthermore, 2-[(2-iodobenzoyloxy)methyl]-4-imidazolidinone was derivatized by solvolysis and Sonogashira coupling. DFT calculations indicated that the double Michael addition mechanism is plausible. Thus, the potential of an unsubstituted EBX reagent for the synthesis of heterocycles from complex molecules and their functionalization with mild nucleophiles was demonstrated
Enantioselective Organocatalytic Double Michael Addition Reactions
No full textA novel organocatalytic, enantioselective domino double Michael addition reaction of α,β-unsaturated aldehydes with ethyl 4-mercapto-2-butenoate has been developed. The process is promoted by chiral diphenylprolinol TMS ether to give chiral tetrahydrothiophenes in high to
excellent levels of enantioselectivities
Double Michael adducts: Source for spiro heterocycles
No full text283-289The gem cyano ester functionality in double
Michael adduct, 4-carboethoxy-2-carbomethoxy-4-cyano-3,5-diaryltetra-hydro[2H]thiopyran-1,1-dioxide 1 has been exploited to develop three
different types of spiro heterocycles viz.,
spiro pyrimidine, pyrazole and isoxazole derivatives in the presence of
appropriate nucleophiles
Enantioselective Organocatalytic Double Michael Addition Reactions
No full textA novel organocatalytic, enantioselective domino double Michael addition reaction of α,β-unsaturated aldehydes with ethyl 4-mercapto-2-butenoate has been developed. The process is promoted by chiral diphenylprolinol TMS ether to give chiral tetrahydrothiophenes in high to
excellent levels of enantioselectivities
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Double Michael reaction of N-carboethoxy-2,3-dihydropyridin-4-one
No full textReaction of the enolate of N-ethoxycarbonyl-3,4-dihydropyridin-4-one with methyl acrylate provided N-ethoxycarbonyl-2-azabicyclo [2.2.2] -7-methoxycarbonyloctan-5-one by diastereoselective double Michael addition reaction
A Heterocycle-Forming Double Michael Reaction. [5 + 1] Annulation Route to Highly Substituted and Functionalized Piperidines
No full textNitrogen-containing tethered diacids, easily prepared by reductive alkylation of diethyl aminomalonate or ethyl cyanoglycinate, undergo double
Michael reactions with 3-butyn-2-one to give highly functionalized and substituted piperidines (pipecolic acid derivatives) with surprisingly
high stereoselectivity. The heterocyclic double Michael adducts can be induced to undergo further cyclizations to give a variety of azabicyclic
and diazabicyclic compounds
A Heterocycle-Forming Double Michael Reaction. [5 + 1] Annulation Route to Highly Substituted and Functionalized Piperidines
No full textNitrogen-containing tethered diacids, easily prepared by reductive alkylation of diethyl aminomalonate or ethyl cyanoglycinate, undergo double
Michael reactions with 3-butyn-2-one to give highly functionalized and substituted piperidines (pipecolic acid derivatives) with surprisingly
high stereoselectivity. The heterocyclic double Michael adducts can be induced to undergo further cyclizations to give a variety of azabicyclic
and diazabicyclic compounds
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