Showing papers by "Samir Z. Zard published in 2003"
TL;DR: A short synthesis of the tricyclic skeleton of pleuromutilin is reported, featuring an unusually efficient 8-endo-trig radical cyclization of a xanthate precursor.
47 citations
TL;DR: S-[1-(N-Acetylamino)-2, 2,2,2-trifluoroethyl]-O-ethyl dithiocarbonate adds efficiently to various functionalized olefins to give the corresponding adducts 8 via a radical chain reaction initiated by a small amount of lauroyl peroxide.
46 citations
01 Jan 2003
TL;DR: In this article, the structural effect of miscellaneous xanthates RS(C=S)OZ' on the level of control of free radical polymerizations was investigated, and it was shown that the more substituted and stabilized the R leaving group, the better the control over molar masses as a function of the monomer conversion.
Abstract: The structural effect of miscellaneous xanthates RS(C=S)OZ' on the level of control of free radical polymerizations was investigated. Such polymerizations referred as to the MADIX process involve the use of xanthates as reversible chain transfer agents (CTAs). In the case of S-alkyl-O-ethyl xanthates, RS(C=S)OEt, the process involves slow degenerative transfer of xanthate end-groups between polymer chains. This leads to styrene and acrylate-derived polymers with predetermined molar masses at high conversion and polydispersity index (PDI) between 1.5 and 2. In this series, the more substituted and stabilized the R leaving group, the better the control over molar masses as a function of the monomer conversion. Excellent control can be achieved in the polymerization of vinyl esters, acrylic acid and acrylamide. The reactivity of the C=S double bond of xanthates can be dramatically increased towards polystyryl and polyacrylyl radicals by incorporating electron-withdrawing substituents in the activating Z=OZ' group of S-(1-ethoxycarbonyl)ethyl-O- alkyl xanthates, C2H5OCO(CH3)CH-S(C=S)OZ'. This allows the preparation of polymers with controlled molar masses and PDI close to unity.
44 citations
TL;DR: Various acyl radicals can be generated from the corresponding acyl triphenylmethyldiazo derivatives, produced by in situ oxidation of hydrazide precursors with phenylseleninic acid.
38 citations
TL;DR: Amidinyl radicals are readily generated from amidoxime benzoates by treatment with a stannane-diazo initiator or with Ni-AcOH and captured by an internal olefin to give the corresponding imidazoline.
34 citations
TL;DR: A short synthesis of (+/-)-10-norparvulenone and (+/--O-methylasparvenone was developed starting from commercially available m-methoxyphenol, hinging on a xanthate-mediated addition-cyclization sequence for the construction of the alpha-tetralone subunit.
29 citations
TL;DR: Potassium O-ethyl xanthate readily adds to alpha,beta-unsaturated nitro compounds to give stable beta-nitro xanthates, which undergo tin-free elimination to form olefins in good yield and good E selectivity upon simple heating with lauroyl peroxide in refluxing 1,2-dichloroethane.
22 citations
TL;DR: In this paper, the Wittig-Horner-Emmons reaction was used to give cyclohexene and cycloheptene rings fused to the cyclobutane.
18 citations
TL;DR: Xanthate-mediated intermolecular radical addition, hydrogen atom transfer and sulfonyl radical elimination have been efficiently combined in a new convergent synthesis of ketones and substituted olefins as discussed by the authors.
14 citations
TL;DR: Treatment of a geminal pivaloxy xanthate with vinyl pivalate gives a 1,3-dithietanone, a little known class of compounds.
9 citations
Patent•
11 Sep 2003TL;DR: In this paper, a method for the preparation of compounds having the general formula (I) and the use of such compounds in organic radical synthesis is described. But this method is restricted to compounds having a general formula.
Abstract: The invention relates to compounds having the general formula (I), the method of preparation thereof and the use thereof in organic radical synthesis. The invention also relates to compounds having the formula (II), the method of preparation thereof and a method for preparing compounds having the formula (VIII).
TL;DR: In this paper, various acyl radicals can be generated from the corresponding acyl triphenylmethyldiazo derivatives, produced by in situ oxidation of hydrazide precursors with phenylseleninic acid.
Abstract: Various acyl radicals can be generated from the corresponding acyl triphenylmethyldiazo derivatives, produced by in situ oxidation of hydrazide precursors with phenylseleninic acid.
TL;DR: Various xanthates, made by conjugate addition of xanthic acid to electrophilic olefins, add in a inter- or intra-molecular fashion to olefs allowing a direct introduction of a quaternary centres and the construction of polycyclic structures as discussed by the authors.
Abstract: Various xanthates, made by conjugate addition of xanthic acid to electrophilic olefins, add in a inter- or intra-molecular fashion to olefins allowing a direct introduction of a quaternary centres and the construction of polycyclic structures.
TL;DR: The complex antibacterial natural product, pleuromutilin, can be directly modified by the radical addition reaction of various xanthates to the unactivated terminal olefin present on C-12.
Abstract: The complex antibacterial natural product, pleuromutilin, can be directly modified by the radical addition reaction of various xanthates to the unactivated terminal olefin present on C-12.
TL;DR: Xanthate derivatives of tetraalkylmethylenebisphosphonate add efficiently to various functionalised olefins to give the corresponding adducts via a radical chain reaction initiated by a small amount of lauroyl peroxide as mentioned in this paper.
Abstract: Xanthate derivatives of tetraalkylmethylenebisphosphonate add efficiently to various functionalised olefins to give the corresponding adducts via a radical chain reaction initiated by a small amount of lauroyl peroxide.
TL;DR: In this paper, a cascade involving aryl migration and elimination of a sulfonyl radical is described, with the result being an overall homoallylation of the initial radical.
Abstract: Xanthate addition to 3-aryl-4-methanesulfonylbutene and structurally related derivatives triggers a cascade involving aryl migration and elimination of a sulfonyl radical, the result being an overall homoallylation of the initial radical. Other slow migrating groups such as an ester can replace the aryl group.
Patent•
20 May 2003
TL;DR: In this paper, a method of controlled radical co-polymerization for block-copolymers with low index of polydispersion and having chain terminal functional groups was presented.
Abstract: FIELD: chemistry of polymers, chemical technology. SUBSTANCE: invention relates to novel method of radical polymerization allowing to prepare block-copolymers and to block-copolymers prepared by this method. Method involves interaction of ethylene-unsaturated monomer of the formula CYY'(=CW-CW')a=CH2, compound-precursor synthesized by radical polymerization of ethylene-unsaturated monomer of the formula CXX'(=CV-CV')b=CH2 in the presence of alkylxanth, initiating agent of radical polymerization. Invention provides the development of method of controlled radical co-polymerization for preparing block-copolymers with low index of polydispersion and having chain terminal functional groups. EFFECT: improved method of synthesis. 16 cl, 12 tbl
TL;DR: The radical addition of a-xanthyl ketones to vinyl pivalate gives adducts that are synthetic equivalents of 1,4-ketoaldehydes; treatment with ammonia or primary amines leads to the corresponding pyrroles in high yield.
Abstract: The radical addition of a-xanthyl ketones to vinyl pivalate gives adducts that are synthetic equivalents of 1,4-ketoaldehydes; treatment with ammonia or primary amines leads to the corresponding pyrroles in high yield.
TL;DR: In this paper, it was shown that amidoxime radicals are readily generated from benzoates by treatment with a stannane-diazo initiator or with Ni-AcOH and captured by an internal olefin to give the corresponding imidazoline.
Abstract: Amidinyl radicals are readily generated from amidoxime benzoates by treatment with a stannane-diazo initiator or with Ni-AcOH and captured by an internal olefin to give the corresponding imidazoline.
TL;DR: The six-membered heterocyclic subunit of homophthalimides can be obtained by a direct, hitherto unprecedented, radical cyclisation onto an aromatic ring starting from a xanthate precursor.
Abstract: The six-membered heterocyclic subunit of homophthalimides can be obtained by a direct, hitherto unprecedented, radical cyclisation onto an aromatic ring starting from a xanthate precursor.
TL;DR: The radical reaction between an N-ethylsulfonylenamide and an α-xanthyl ketone gives an intermediate γ-keto imine which spontaneously ring-closes to the pyrrole as discussed by the authors.
Abstract: The radical reaction between an N-ethylsulfonylenamide and an α-xanthyl ketone gives an intermediate γ-keto imine which spontaneously ring-closes to the pyrrole.
TL;DR: In this article, an intermolecular radical addition of a xanthate to vinyl pivalate gave a 1,3-dithietanone, a little known class of compounds.
Abstract: Treatment of a geminal pivaloxy xanthate, prepared by an intermolecular radical addition of a xanthate to vinyl pivalate, gives a 1,3-dithietanone, a little known class of compounds.
TL;DR: Xanthate-mediated intermolecular radical addition, hydrogen atom transfer and sulfonyl radical elimination have been efficiently combined in a new convergent synthesis of ketones and substituted olefins as mentioned in this paper.
Abstract: Xanthate-mediated intermolecular radical addition, hydrogen atom transfer and sulfonyl radical elimination have been efficiently combined in a new convergent synthesis of ketones and substituted olefins.
TL;DR: In this article, various xanthates add efficiently to olefins bearing [1,2,4]triazole, imidazole or benzimidazoles moieties via a radical chain reaction initiated by a small amount of lauroyl peroxide.
Abstract: [reaction: see text] Various xanthates add efficiently to olefins bearing [1,2,4]triazole, imidazole, or benzimidazole moieties in the presence of camphorsulfonic acid via a radical chain reaction initiated by a small amount of lauroyl peroxide. The adducts may be transformed to more complex molecules by implementing a further radical cyclization.