bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal Complexes of Pentadentate Macrocyclic Ligands Containing Oxygen and Nitrogen as Donor Atoms
Authors: Cabral M. Fátima , Delgado Rita 
Published: December 2004

AbstractFour macrocyclic ligands have been synthesized: 1‐oxa‐4,7,10,13‐tetraazacyclopentadecane (1), 1,4‐dioxa‐7,10,13‐triazacyclopentadecane (2), 1,4‐dioxa‐7,11,14‐triazacyclohexadecane (3), 1,4‐dioxa‐7,11,15‐triazacycloheptadecane (4), one of them 3, for the first time. The protonation constants of the ligands and the stability constants of the complexes formed by the four ligands with some divalent first‐series transition‐metal ions, Cd2+ and Pb2+, were determined by potentiometric methods, in aqueous solution, at 25° and I = 0.10M (KNO3). The sequence of protonation of ligand 1 was studied by 1H‐NMR spectroscopy. The Irving‐Williams' order of stability is obeyed for the complexes of all the ligands, and the metal complexes of 1 present the higher values of stability. A drop in the stability of all the metal complexes studied is observed when the metal complexes of 1 are compared with the corresponding complexes of 2. The effect of the increase of the ring size of the macrocycle can be observed for metal complexes of the series of ligands 2 4, where, in spite of the slight increase of the overall basicity of the ligands (20.28, 22.25, and 24.96 for 2, 3, and 4 respectively), small differences in stability are found for the corresponding complexes of 2 and 3, but a significant drop occurs for all the metal complexes formed with the 17‐membered ligand, specially for the larger metal ions like Mn2+ and Pb2+.
Synthesis and Conformational Analysis of 2′‐Deoxy‐2′‐(3‐methoxybenzamido)adenosine, a rational‐designed inhibitor of trypanosomal glyceraldehyde phosphate dehydrogenase (GAPDH)
Authors: Van Calenbergh Serge , Van Den Eeckhout Elfride , Herdewijn Piet , De Bruyn André , Verlinde Christophe , Hol Wim , Callens Mia , Van Aerschot Arthur , Rozenski Jef 
Published: December 2004

AbstractA series of 2′‐benzamido‐2′‐deoxyadenosine analogues were synthesized in an effort to find new lead structures for the treatment of sleeping sickness. The 2′‐deoxy‐2′‐(3‐methoxybenzamido)adenosine (1h) was proved to be a selective inhibitor of the parasite glyceraldehyde 3‐phosphate dehydrogenase which confirms the modeling studies. The solution‐state conformation of 2′‐(thiophene‐2‐carboxamido) analogue 1d demonstrates a 2′‐endo conformation, an orientation of the thiophene ring under the ribose moiety, and the base part occupying a ‘syn’/‘anti’ equilibrium.
Organic Reactions in the Solid State: The reactivity of guest molecules in tri‐o‐thymotide clathrates
Authors: Gerdil Raymond , Barchietto Giacomo 
Published: December 2004

AbstractTri‐o‐thymotide (TOT) clathrates are enantiomorphous and enantioselective (chiral cages). It was shown that an external molecular reactant can diffuse into the TOT host crystal lattice and reacts with the included molecule (guest) in characteristic ways, differing from those occurring in liquid solutions. Several aspects of the action of hydrogen halides (HCl, HBr) on the chemical behavior of included oxiranes were investigated for solid‐gas and solid‐liquid (aqueous) systems. Under well established experimental conditions, these reactions gave regiospecifically one target product and were asymmetric. The included substrate underwent first an acid‐catalyzed allylic isomerization that is cage‐specific and mostly quantitative. In sheer contrast, strong basic conditions were required to promote, in reduced yield, the analogous transformation in solution. The regiospecificity and enantioselectivity of several intra‐crystalline conversions allowed the accurate determination of the absolute configuration of several guest molecules. Kinetic measurements were achieved that disclosed some striking features of this new type of heterogeneous reactions. Tentative models for the cage stereoselective mechanisms are briefly discussed.
Macrocyclische Imide: Vielseitige Synthese‐Bausteine bei Ringerweiterungsreaktionen
Authors: Koch Thomas , Hesse Manfred 
Published: December 2004

Macrocyclic Imides: Versatile Synthons in Ring‐Enlargement ReactionsMacrocyclic imides differ from phthal‐ or succinimids in their increased electrophilicity. This property makes them versatile synthons for reactions with several nucleophiles. If a nucleophile is attached to the N‐substituent of the imide, an intramolecular reaction will occur leading to ring‐enlarged products. Use of N, O, and C nucleophiles for this synthetic pathway is reported. Synthetic transformations of e.g. cyclododecanone leads to 17‐, 18‐, or 19‐membered macrolides, 11, 12, 15, 16, 21, 27, 30, in three to five steps.
N4‐Benzoylspermidine from Oncinotis tenuiloba: Analytical differentiation of the three isomeric N‐benzoylspermidines
Authors: Doll Martin K.‐H. , Guggisberg Armin , Hesse Manfred 
Published: December 2004

AbstractDuring the examination of extracts from Oncinotis tenuiloba STAPF a new polyamine, N4‐benzoylsperimidine (8), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative 13, and the three possible N‐benzoyl‐substituted isomers of spermidine 5, 8, and 11 together with their peracetylated derivatives 12–14, respectively, were synthesized and identified.
Synthesis of the Thiazolone Analogue of the Acetylcholinesterase Inhibitor, Huperzine A
Authors: Kozikowski Alan P. , Tückmantel Werner , Saxena Ashima , Doctor Bhupendra P. 
Published: December 2004

AbstractThe preparation of an analogue 3a of the acetylcholinesterase inhibitor, huperzine A (1), is described in which the pyridinone moiety of the natural product is replaced with a thiazolone moiety. The synthesis started from cyclohexane‐1,4‐dione monoethylene ketal (7) by first annulating the thiazole ring using the Gewald protocol (→ 8; Scheme 1) and then constructing the bicyclo[3.3.1]nonane substructure using our previously described Michael addition/aldol condensation methodology (Scheme 3). The central problem was the protection of the thiazolone carbonyl group; only the 2‐unsubstituted thiazole survived the reaction conditions of the first half of the synthesis. Refunctionalization was later effected by lithiation and subsequent chlorination with hexachloroethane (30→31). Compound 3a was ineffective in the acetylcholinesterase inhibition assay in concentrations up to 14 μM.
A Reinvestigation of the Oxidative Rearrangement of Yohimbane‐Type Alkaloids. Part A. Formation of pseudoindoxyl ( = 1,2‐dihydro‐3H‐indol‐3‐one) derivatives
Authors: Stahl Reto , Borschberg Hans‐Jürg 
Published: December 2004

AbstractContrary to earlier reports, the base‐induced rearrangement of the 7‐hydroxy‐7H‐indolenines derived from ajmalicine (1), yohimbine (5), corynanthine (6), methyl reserpate (16), and methyl isoreserpate (17) in each case furnished not just one, but two epimeric spiro‐pseudoindoxyl derivatives which have opposite configuration at the spiro centre C(2). In all cases, the major component was shown by NOE experiments to be the A‐type isomer (carbonyl group located below the plane defined by rings C and D). The thermodynamically less stable B‐type pseudoindoxyl epimers 4, 10, 12, and 22 were isolated and characterized for the first time.
On the Stacking of β ‐Rings: The solution self‐association behavior of two partially N‐methylated cyclo(hexaleucines)
Authors: Sun Xicheng , Lorenzi Gian Paolo 
Published: December 2004

AbstractCyclo(‐D‐Leu‐L‐MeLeu‐D‐Leu‐L‐MeLeu‐D‐Leu‐L‐MeLeu‐) (1) and cyclo(‐L‐Leu‐D‐Leu‐L‐MeLeu‐D‐Leu‐L‐Leu‐D‐Leu‐) (2) were synthesized and used for a study of the interaction of β ‐rings in solution. In appropriate solvents, 1 and 2 formed dimers consisting of two β ‐rings connected through six interannular H‐bonds and having the N ‐Me group(s) on the solvent‐exposed face. The study also afforded indications that 2 formed different dimers of this kind, differing in the relative orientation of the two β ‐rings. These experimental observations provide strong support to the idea that unsubstituted D,L‐alternating cyclooligopeptides, such as cyclo(hexaleucine), can self‐assemble and give rise to long tubular stacks of β ‐rings.
Permanganate Oxidation of Quinoxaline and Its Derivatives
Authors: Obafemi Craig A. , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe oxidation reactions of a series of quinoxaline derivatives, using KMnO4 in the presence or absence of NaOH, are described. Neutral oxidation of 2‐chloro‐ and 2, 3‐dichloroquinoxalines 2–4 afforded the corresponding chloro‐ and dichloropyrazinedicarboxylic acids 13 and 14 in good yield. On the other hand, oxidation of quinoxalin‐2(1H)‐one and 1, 4‐dihydroquinoxaline‐2, 3‐dione derivatives in alkaline medium gave different products, with the quinoxalin‐2(1H)‐one (5) forming 1, 4‐dihydroquinoxaline‐2, 3‐dione (9), while various substituted quinoxalin‐2, 3‐dione derivatives (see 9–11) gave a new type of dimeric products. The structural assignments for the new compounds were based on spectroscopic data.
Synthesis of 3‐Methoxy‐ and 3‐(β‐D‐Glucopyranosyloxy)flavylium Ions. Influence of the flavylium substitution pattern on the reactivity of anthocyanins in aqueous solution
Authors: Dangles Olivier , Elhajji Hakima 
Published: December 2004

AbstractThe synthesis of 3‐glycosyloxylated flavylium ions (anthocyanins), in particular of callistephin (4), a natural anthocyanin, is described. The structural transformations in aqueous solution and molecular complexation with chlorogenic acid (7) and caffeine (8) of the synthesized pigments 3 and 4 are investigated and compared to those of the corresponding 3‐methoxyflavylium ions 1 and 2 and to those of oenin (5) and malvin (6), two very common natural anthocyanins. The results are discussed in terms of the role played by the glycosyloxy residues in the chemical properties of anthocyanins. Anthocyanin molecular complexation (copigmentaion) is quantitatively investigated by UV/VIS spectroscopy and 1H‐NMR. In particular, the UV/VIS spectroscopic data are interpreted using a general theoretical treatment, which, e.g., allows to demonstrate the formation of molecular complexes between the colourless forms of an anthocyanin and 8.
Synthesis and Characterization of New Phthalocyanines Peripherally Fused to Four 13‐Membered Tetrathiamacrocycles
Authors: Gürek Ayşe G. , Bekâroǧlu özer 
Published: December 2004

AbstractThe new metal‐free phthalocyanine 5 and phthalocyaninatometals 6–8 (M=Co, Ni, or Zn) fused in peripheral positions with four 13‐membered tetrathiamacrocycles were prepared by cyclotetramerization of 2, 3, 6, 7, 9, 10‐hexahydro‐5H‐[1, 4, 8, 11]benzotetrathiacyclotridecine‐13, 14–dicarbonitrile in the presence of a suitable metal salt or a strong organic base. In contrast to the aza‐ or oxamacrocycle‐fused analogs, the solubility of these phthalocyanines is very low. Complexation of the tetrathiamacrocycles of 7 and 8 with PdII or AgI to form pentanuclear products was accomplished from their suspensions.
Rhodenthoside A, a New Type of Acylated Secoiridoid Glycoside from Gentiana rhodentha
Authors: Ma Wei‐Guang , Fuzzati Nicola , Wolfender Jean‐Luc , Hostettmann Kurt , Yang Chong‐Ren 
Published: December 2004

AbstractInvestigation of the metabolites from Gentiana rhodentha FR. (Gentianaceae) by LC‐UV and LC‐MS resulted in the isolation and identification of a new type of secoiridoid glycoside, rhodenthoside A (1), together with the known secoiridoids sweroside (2) and swertiamarin (3), as well as the known iridoids kingiside (4) and 8‐epikingiside (5). The structures were established by 1D‐ and 2D‐NMR, EI‐MS, D/CI‐MS, FAB‐MS, CF‐FAB, LC‐MS, TSP, LC‐MS, and LD‐MS data in combination with chemical reactions.
Metal‐Ion‐Coordinating Properties of a Viral Inhibitor, a pyrophosphate analogue, and a herbicide metabolite, a glycinate analogue: The solution properties of the potentially five‐membered chelates derived from phosphonoformic acid and (aminomethyl)phosphonic acid
Authors: Song Bin , Chen Dong , Bastian Matthias , Sigel Helmut , Bruce Martin R. 
Published: December 2004

AbstractThe pyrophosphoric‐acid‐analogue phosphonoformic acid (pfa) and the amino‐acid‐analogue (aminomethyl)phosphonic acid (ampa) both form, in the deprotonated state, i.e., as –OOC–PO and H2NCH2PO, respectively, five‐membered chelate rings with metal ions. pfa inhibits both phosphate transport and virus replication, while ampa is a metabolic product of the common herbicide glyphosate (  N‐(phosphonomethyl)glycine). The acidity constants of H2pfa– and H2ampa± as well as the stability constants of the [M(Hpfa)], [M(pfa)]–, [M(Hampa)]+, and [M(ampa)] complexes, where M2+  Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Cu(2,2′‐bipyridyl)2+, Cu(1,10‐phenanthroline)2+, Zn2+, or Cd2+, have been determined by potentiometric pH titrations in aqueous solution at 25° and I  0.1M (NaNO3). The structures of isomeric complexes and the connected intramolecular equilibria are deduced and evaluated based on the equilibrium constants measured and those calculated via the pKa values of the above mentioned ligands and previously established log K vs. pKa straight‐line plots (H. Sigel et al., Helv. Chim. Acta 1992, 75, 2634) for a simple phosphonate‐M2+ coordination. pfa forms stronger complexes than ampa with all the above mentioned metal ions, with the single exception of [Cu(ampa)] which is slightly more stable than [Cu(pfa)]–. In neutral solutions, more precisely at pH of ca. 6, pfa complexes of alkaline‐earth‐metal ions retain one phosphonate‐bound proton, [M(Hpfa)], while those of the transition‐metal ions chelate with the trianionic ligand, pfa3–. In accord with increasing ligand‐basicity, the stability‐constant order for all metal‐ion complexes is oxalate > pfa > pyrophosphate but, owing to proton competition in pyrophosphate, in neutral solutions metal‐ion complexation of pfa3– competes with P2O. With ampa alkaline‐earth‐metal ions interact only with the phosphonate group of even the dianionic ligand (though Mg2+ appears to form a low fraction of a [Mg(ampa)] chelate) while transition‐metal ions form chelates which are comparable in stability to those of glycinate.
Synthesis and Complexation Properties of a New Class of Receptors based on a cone‐configurated tetra‐p‐(tert‐butyl)calix[4]arene and bipyridyl subunits
Authors: de Vains Jean‐Bernard Regnouf , Lamartine Roger 
Published: December 2004

Abstract0The bipyridyl‐armed tetra‐p‐(tert‐butyl)calix[4]arenes 1–5 were synthesized from tetra‐p‐(tert‐butyl)‐calix[4]arene A and 6‐(bromomethyl)‐6′‐methyl‐2,2′‐bipyridine (B) by direct base‐strength‐driven regioselective O‐alkylation or by stepwise procedures. Preliminary complexation studies of the ligands 1–3 with CuI affording the complexes 6–8 are described.
A New Triterpene Saponin from Heteropappus biennis with an Unusual Carbohydrate Chain
Authors: Bader Gerd , Danzandarjaa Tuja , Hiller Karl , Reznicek Gottfried , Jurenitsch Johann , Golly Monika , Schröder Harald , Schubert‐Zsilavecz Manfred , Haslinger Ernst 
Published: December 2004

AbstractA new saponin, O‐α‐D‐arabinopyranosyl‐(1→6)‐O‐[α‐L‐rhamnopyranosyl‐(1→2)]‐O‐[β‐D‐xylopyranosyl‐(1→3)]‐β‐D‐glucopyranosyl arjunolate (1) was isolated from the flowers of Heteropappus biennis (LDB.) TAMAMSCH. The structure was established mainly by a combination of 1D selective and 2D NMR techniques like COSY, TOCSY, ROESY, HMQC, and HMBC. Molecular‐modelling calculations showed that the oligosaccharide chain is rather rigid. Six minimum structures are discussed.
Preparation and Structure of Oligolides from (R)‐3‐Hydroxypentanoic Acid and comparison with the hydroxybutanoic‐acid derivatives: A small change with large consequences
Authors: Seebach Dieter , Hoffmann Torsten , Kühnle Florian N. M. , Lengweiler Urs D. 
Published: December 2004

AbstractCyclic oligomers of (R)‐3‐hydroxyvaleric acid (3‐HV) are prepared from the monomer by three different methods, giving various ratios of the oligomers. The macrocycles containing three to twelve 3‐HV units (12‐ to 48‐membered rings) are isolated in pure form by chromatography. The triolide 3 can be separated by distillation and isolated on large scale. Biopol, the copolymer of (R)‐3‐hydroxybutanoic acid (3‐HB) and (R)‐3‐hydroxyvaleric acid (3‐HV), is degraded to mixtures of Me‐ and Et‐substituted triolides (‘mixolides’) with high crystallization tendency. The X‐ray crystal structures of the tetrolide 4, pentolide 5, hexolide 6, heptolide 7, and of two ‘mixolides’ (with inclusions of solvent) have been determined (Figs. 3–7, 10, and 11) and are compared with those of the corresponding 3‐HB derivatives reported previously. From the structural data, a 31 and a 21 helix of 3‐HV can be modelled, and the latter one compared with helix structures of P9(3‐HB) and P(3‐HV) derived from stretch‐fibre X‐ray scattering. Crystals of a water‐containing NaSCN complex of the triethyl triolide 3 were obtained in good quality for X‐ray analysis. The structure (Figs. 12, 13, and Table 6) contains an interesting array of CO and H2O O‐atoms around the Na+ ions along a channel‐type tube (a‐axis of the crystal) which may be relevant to the role of P(3‐HB) and P(3‐HV) as components of cellular ion channels.
Synthesis of Tri‐, Penta‐, and Heptapeptides Containing and (R)‐2‐alkyl‐2‐amino‐3‐(methylamino)‐propionic acid residue in the central position
Authors: Seebach Dieter , Studer Armido , Pfammatter Elmar , Widmer Hans 
Published: December 2004

AbstractBy conventional peptide‐coupling methods (C to N direction; mixed anhydride, bis(2)‐oxooxazolidin‐3‐yl)phosphinoyl chloride (Bop‐Cl), or dicyclohexylcarbodiimide (DCC), 2‐amino‐2‐methyl‐3‐(methylamino)‐propionic acid and 2‐amino‐2‐ethyl‐3‐(methylamino)propionic acid ( = 2‐amino‐2‐[(methylamino)methyl]butanoic acid) are incorporated in the central position of tri‐, penta‐, and heptapeptides (see 3–7, 21, and 22). The fragment coupling of the β ‐amino group of the diamino‐acid moiety in a tetrapeptide led to partial epimerization, and thus, two epimeric heptapeptide derivatives were actually obtained (7 and epi‐7). The final deprotection to the free heptapeptide (involving a Me3SiI cleavage of BocNH and MeOCONH, a saponification with NaOH, and HPLC purification) gave both the desired product (isopeptide 21), with the β ‐amino group inside the peptide backbone, and a product (peptide 22) of transpeptidation, with the α‐amino group of the diamino acid incorporated and a (methylamino)methyl group as the side chain. Peptide 22 is completely converted to the isopeptide 21 by prolonged treatment with base. The heptapeptide 21 was analyzed by elaborate 2QF‐COSY and NOESY NMR measurements in H2O/CD3OD at −5° (Table, Fig.); there is no indication for β ‐sheet or helical structures, a fact which was also confirmed by CD measurements.
Chemie von α‐Aminonitrilen. 12. Mitteilung. Sondierungen über thermische Umwandlungen von α‐Aminonitrilen
Authors: Xiang Yi‐Bin , Drenkard Susanne , Baumann Karl , Hickey Deirde , Eschenmoser Albert 
Published: December 2004

Chemistry of α‐Amino Nitriles11. Mitteilung: [1].

.
Exploratory Experiments on Thermal Reactions of α‐Amino Nitriles
The paper extends a previously published report [4] on chemical properties of α‐amino nitriles and of members of the C3H4N2 ensemble (Scheme 1) as observed in experiments carried out under non‐aqueous conditions. The reactions investigated and the observations made are summarized in some detail in the English footnotes (*) referring to Schemes 1–17 and Fig. 1.
Hetero‐Diels‐Alder Additions of α,β‐Unsaturated‐Acyl Cyanides. Part 3. Syntheses of 3‐bromo‐2‐ethoxy‐3,4‐dihydro‐2H‐pyran‐6‐carbonitriles, and about their transformation to 2‐ethoxy‐2H‐pyrans
Authors: Zhuo Jin‐Cong , Wyler Hugo , Schenk Kurt 
Published: December 2004

AbstractCycloadditions of the α,β‐unsaturated‐acyl cyanides 1–3 with (Z)‐or (E)‐1‐bromo‐2‐ethoxyethene (4) may be performed at moderate temperatures and provide in good yields the 3‐bromo‐2‐ethoxy‐3,4‐dihydro‐2H‐pyran‐6‐carbonitriles 5–7, respectively (Scheme 1). Diastereoisomeric pairs of products result at room temperature merely from the ‘endo’‐ and ‘exo’‐transition states; more complex mixtures appear above 60° as a consequence of (Z)/(E)‐isomerization of 4. The relative stability of the anomers of 5 and 6 is explored by treatment with BF3·Et2O. Acid alcoholysis (MeOH or EtOH) of 5 leads to acetals 9a, b of 4‐bromo‐5‐oxopentanoate. Alkyl (2Z,4E)‐5‐ethoxypenta‐2,4‐dienoates 12, 17, and 20, are formed in alcoholic alkoxide solutions from 5, 6, and 7, respectively, which is compatible with the intermediacy of 2‐alkoxy‐2H‐pyrans and their valence tautomers, α,β‐unsaturatedacyl cyanides. Methoxide addition to the CN group competes with dehydrobromination in case of 5; it leads to 3‐bromo‐3,4‐dihydro‐2H‐pyran‐6‐carboximidate 13 (ca. 50% at −20°) which can be hydrolyzed to the methyl carboxylate 14. DBU (1,8‐diazabicyclo[5,4,0]undec‐7‐ene) in benzene converts 5 to 6‐ethoxy‐2‐oxohexa‐3,5‐dienenitrile (11), the ring‐opening product of an obviously unstable 2‐ethoxy‐2H‐pyran; the same reagent dehydrobrominates 6 to 2‐ethoxy‐4‐methyl‐2H‐pyran‐6‐carbonitrile (15). HBr Elimination from 7 takes place with great ease in presence of pyridine, or even during chromatography on alumina, and leads to the stable ethyl 6‐cyano‐2‐ethoxy‐2H‐pyran‐4‐carboxylate (18); this dimerizes at room temperature to give a 1:3 mixture of tricyclic adducts ‘endo’‐21 and ‘exo’‐21. The structure of the latter is established by an X‐ray crystallographic analysis.
Preparation and Absolute Configuration of Some Iris Essential Oil Constituents of the 5‐methylsafranic‐acid series
Authors: Chapuis Christian , Schulte‐Elte Karl H. 
Published: December 2004

AbstractThe β‐dienoate (+)‐(5S)‐13a (86% ee; meaning of α and β as in α‐ and β‐irone, resp.) was obtained from (−)‐(5S)‐9a via acid‐catalyzed dehydration of the diastereoisomer mixture of allylic tertiary alcohols (+)‐(1S,5S)‐15/(+)‐(1R,5S)‐15 (Scheme 3). Prolonged treatment gave clean isomerization via a [1,5]‐H shift to the α‐isomer (−)‐(R)‐16a with only slight racemization (76% ee; Scheme 4). In contrast, the SnCl4‐catalyzed stereospecific cyclization of (+)‐(Z)‐6 to (−)‐trans‐8a (Scheme 2), followed by a diastereoselective epoxidation to (+)‐11 gave, via acid‐catalyzed dehydration of the intermediate allylic secondary alcohol (−)‐12, the same ester (+)‐13a (Scheme 3), but with poor optical purity (13% ee), due to an initial rapid [1,2]‐H shift. The absolute configuration of (−)‐16a–c was confirmed by chemical correlation with (−)‐trans‐19 (Scheme 4). 13C‐NMR Assignments and absolute configurations of the intermediate esters, acids, aldehydes, and alcohols are presented.
Absolute Rate Constants for the Addition of Cyanomethyl (·CH2CN) and (tert‐Butoxy)carbonylmethyl (·CH2CO2C(CH3)3) radicals to alkenes in solution
Authors: Wu Jie Qiang , Beranek Ivan , Fischer Hanns 
Published: December 2004

AbstractAbsolute rate constants and their temperature dependence were determined by time‐resolved electron spin resonance for the addition of the radicals ·CH2CN and ·CH2CO2C(CH3)3 to a variety of mono‐ and 1,1‐disubstituted and to selected 1,2‐ and trisubstituted alkenes in acetonitrile solution. To alkenes CH2CXY, ·CH2CN adds at the unsubstituted C‐atom with rate constants ranging from 3.3·103 M−1S−1 (ethene) to 2.4·106 M−1S−1 (1,1‐diphenylethene) at 278 K, and the frequency factors are in the narrow range of log (A/M−1S−1) = 8.7 ± 0.3. ·CH2CO2C(CH3)3 shows a very similar reactivity with rate constants at 296 K ranging from 1.1·104 M−1S−1 (ethene) to 107 M−1S−1 (1,1‐diphenylethene) and frequency factors log (A/M−1S−1) = 8.4 ± 0.1. For both radicals, the rate constants and the activation energies for addition to CH2CXY correlate well with the overall reaction enthalpy. In contrast to the expectation of an electro‐ or ambiphilic behavior, polar alkene‐substituent effects are not clearly expressed, but some deviations from the enthalpy correlations point to a weak electrophilicity of the radicals. The rate constants for the addition to 1,2‐ and to trisubstituted alkenes reveal additional steric substituent effects. Self‐termination rate data for the title radicals and spectral properties of their adducts to the alkenes are also given.