bluuebunny/crossref_metadata_2025 huggingface dataset:
Kohlenwasserstoffverbrückte Komplexe, XXV[1] C–C‐Kupplung von anionischen Tricarbonylmangan‐Komplexen cyclischer Polyene mit kationischen Tropylium‐Metallverbindungen; Darstellung und Struktur von (OC)3Mn(μ‐η5:η6‐C7H8–C7H7)M(CO)3, (OC)3Mn(μ‐η5:η6‐C8H10–C7H7)M(CO)3 und (OC)3Mn(μ‐η5:η6‐C8H8–C7H7)M(CO)3(M = Cr, Mo, W)
Authors: Wieser Michael , Sünkel Karlheinz , Robl Christian , Beck Wolfgang
Published: July 2007

Hydrocarbon‐Bridged Complexes, XXV[1]. – C–C Coupling of Anionic Tricarbonyl Manganese Complexes of Cyclic Polyenes with Cationic Tropylium Metal Compounds; Preparation and Structure of (OC)3Mn(μ‐η5:η6‐C7H8‐C7H7)M(CO)3, (OC)3Mn(μ‐η5:η6‐C8H10–C7H7)M(CO)3, and (OC)3Mn(μ‐η5:η5‐C8H8–C7H7)M(CO)3 (M = Cr, Mo, W)

The addition of the anionic complexes [(η4‐C7H8)Mn(CO)3]‐, [(η4‐C8H10)Mn(CO)3]‐ and [(η4‐C8H8)Mn(CO)3]‐ to the cations [(η7‐C7H7)M(CO)3]+ (M = Cr, Mo, W) gives the hydrocarbon‐bridged complexes (OC)3Mn(μ‐η5:η6‐C7H8–C7H7)M(CO)3, (OC)3Mn(μ‐η5:η6‐C8H10–C7H7)M(CO)3, and (OC)3Mn(μ‐η5:η6‐C8H8–C7H7)M(CO)3 (M = Cr, Mo, W). The structures of 4b and 6a have been determined by X‐ray diffraction.
Ein ungewöhnliches Paar Bis(phosphido)‐verbrückter Dieisencarbonylkomplexe: [Fe2(CO)n{μ‐P(tBu)2}(μ‐PCy2)] (n = 5 und 6)
Authors: Waltherη Bernhard , Hartungη Helmut , Böttcher Hans‐Christian , Baumeister Ute , Krug André , Reinholdη Zzjoachim , Jones Zzpeter G.
Published: July 2007

An Unusual Pair of Bis(phosphido)‐Bridged Diiron Carbonyl Complexes: [Fe2(CO)n{μ‐P(tBu)2}(μ‐PCy2)] (n = 5 and 6)

Treatment of Na[Fe2(CO)6(μ‐CO){μ‐P(tBu)2}] with Cy2PCl gives [Fe2(CO)6{μ‐P(tBu)2}(μ‐PCy2)] (1) which loses CO on heating in toluene to afford [Fe2(CO)5{μ‐P(tBu)2}(μ‐PCy2)] (2). Complexes 1 and 2 have been characterized spectroscopically and by X‐ray analyses. The central Fe2P2 unit in 1 is exactly planar whereas in 2 it is somewhat folded.
Synthesewege zu neuen ionischen Ozoniden
Authors: Korber Nikolaus , Jansen Martin
Published: July 2007

Synthetic Routes to New Ionic Ozonides

New synthetic routes to tetraorganylammonium ozonides involving exchange reactions with alkali metal ozonides were investigated. The previously reported reaction between tetraalkylammonium hyperoxides R4N+O2‐ (R = Me, Et) and alkali metal ozonides in liquid ammonia is severely hampered by the difficult synthesis of these hyperoxides; they are unknown for other quaternary ammonium cations. A similar reaction between the easily accessible chlorides of trialkylbenzylammonium ions and KO3 yields mixed ozonides/chlorides due to some solubility of KCl in liquid ammonia. The new compounds BzlMe3N+ (O3‐)0.6Cl‐0.4 (3), BzlEt3N+ (O3‐)0.8Cl0.2‐ (4) and Bzl(nBu)3N+(O3‐)0.5Cl0.5‐ (5) were prepared by this route. – The by far superior route to new ozonides utilizes macroreticular cation exchange resins in liquid ammonia. Batch equilibration between an excess of the appropriate ionic form of the resin and CsO3 produced Me3PhN+O3‐ (6), BzlMe3N+O3‐ (7), Bzl(nBu)3N+O3‐ (8), and (nPr)4N+ O3‐ (9) in almost quantitative yield. Compounds 4, 6, and 7 were studied by single‐crystal X‐ray analysis; the shortening of the ozonide bond length and the widening of the bond angle in comparison to the alkali metal ozonides as well as the possibility of C–H…O hydrogen bonding are discussed. Thermal stabilities were determined by DTA/TG methods, rapid decomposition starts at 59–79°C for 3, 6, and 7 and at 28–56°C for the remaining new ozonides which contain detachable β‐H atoms.
First evidence of unhindered silanimines obtained by flash vacuum thermolysis and vacuum gas‐solid reaction
Authors: Denis Jean‐Marc , Pellerin Zzbruno , Guenot Pierre , Letulle Marguerite , Ripoll Jean‐Louis
Published: July 2007

The unhindered silanimines 1,1‐dimethyl‐N‐phenylsilanimine (2) and N‐isopropyl‐1,1‐dimethylsilanimine (10) have been generated by flash vacuum thermolysis of the N‐allylsilanamine 1 and vacuum gas‐solid reaction of the 1‐chlorosilanamine 9, respectively. The silanimines 2 and 10 have been characterized by MS as well as by chemical trapping to yield 3 or dimerization to the cyclodisilazane 11.
Ein Zirconiumamid‐Komplex mit Si‐β‐H–Zr‐Wechselwirkungen
Authors: Herrmann Wolfgang A. , Huber Norbert W. , Behm Joachim
Published: July 2007

A Zirconium Amide Complex with Si‐β‐H–Zr Interactions

ZrCl4 (1) reacts in diethyl ether with Li[N(SiHMe2)2] (2) to form the title compound of formula [ZrCl(μ‐Cl){N(SiHMe2)2}2]2 (3). A single‐crystal X‐ray structure analysis in combination with IR data provides evidence for an unprecedented type of β‐hydrogen interactions between a silicon‐attached hydrogen atom of the bis(dimethylsilyl)amide ligand and the zirconium atom (Zr–N–Si–H).
Elektroreduktion organischer Verbindungen, 20[ Darstellung von Bicyclo[n.1.0]alkanen durch elektrochemische Reduktion von 1,3‐Dibromcycloalkanen
Authors: Hoffmann Joachim , Voß Jürgen
Published: July 2007

Preparation of Bicyclo[n.1.0]alkanes by Electrochemical Reduction of 1,3‐Dibromocycloalkanes

Good yields of bicyclo[2.1.0]pentane (17) and bicyclo[3.1.0]‐hexane (3) are obtained on electroreduction of the corresponding 1,3‐dibromocycloalkanes. The results do not depend upon the stereochemistry of the starting material (14 vs. 15 or 11 vs. 12).
Asymmetric induction in reductively initiated [2,3]‐Wittig and retro [1,4]‐brook rearrangements of secondary carbanions
Authors: Hoffmann Rolf , Brückner Reinhard
Published: July 2007

The synthesis of O,S‐acetals and the lithium naphthalenide initiated rearrangement reactions thereof are described. O,S‐Acetal 8a resulted from trapping of the 1,4‐dipole 7 with thiophenol. O,S‐Acetals 16a and b were obtained from aldehydes 14a/b by a one‐pot reaction with (trimethylsilyl)prenol, (tri‐methylsilyl)thiophenol, and trimethylsilyl triflate. Upon reduction with lithium naphthalenide all O,S‐acetals delivered α‐lithiated ethers. They rearranged either in a [2,3]‐Wittig mode furnishing the 1,3‐diol derivatives 20a–h/21 with moderate stereoselectivity (syn:anti = 35:65 to 78:22) or underwent retro [1,4]‐Brook rearrangements yielding the α‐silyl ethers 23i–k/24 with still less stereocontrol (syn:anti = 34:66 to 50:50). The mechanistic implications are discussed.
Neue Wege zum Aufbau von Te–N‐Bindungen – Synthese, Struktur und Eigenschaften von Cl6Te2N2S
Authors: Haas Alois , Kasprowski Jörg , Pryka Michael
Published: July 2007

New Routes for the Formation of Te–N Bonds – Synthesis, Structure, and Properties of Cl6Te2N2S

Besides Cl2magnified image (1), the reaction of Se(NSO)2 with TeCl4 leads to the formation of [Se2N2S]22+[TeCl5‐]2 (2) and the bicyclic heterocycle Cl6Te2N2S (3). The latter is also accessible by treating Se(NSO)2 with TeCl3+AsF6‐. Another product of this reaction is the well‐known salt [Se2N2S]22+[AsF6‐] 2. Treatment of TeCl4 with Me3SiNSO in CH2Cl2 provides 3 on a preparative scale. Its structure has been determined by X‐ray crystallography.
Übergangsmetall‐substituierte Diphosphene, XXVII[1] Synthese und Struktur des Diphosphirans (η5‐C5Me5)(CO)2Fe–H[Cr(CO)5]
Authors: Weber Lothar , Kirchhoff Ralf , Stammler Hans‐Georg , Neumann Beate
Published: July 2007

Transition‐Metal‐Substituted Diphosphenes, XXVII[1]. – Synthesis and Structure of the Diphosphirane (η5‐C5Me5)(CO)2Fe–Pmagnified imageH[Cr(CO)5

(η5‐C5Me5)(CO)2FePH2 (5), prepared from (η5‐C5Me5)(CO)2Fe‐P(SiMe3)2 and ethanol, reacts with one equivalent of ClP = C(SiMe3)2 to give the diphosphirane (η5‐C5Me5)(CO)2Femagnified imagePH (8). Compound 8 is converted into the iron chromium complex [(η5‐C5Me5)(CO)2Fe–magnified imageH]Cr(CO)5(9). In contrast, the reaction of 5 with two equivalents of ClP=C(SiMe3)2 results in the formation of the cyclotri‐phosphane [(η5‐C5Me5)(CO)2Fe–magnified image[CH(SiMe3)2] (12). The molecular structure of 9 is elucidated by single‐crystal X‐ray analysis.
Formal coupling of two alkylidyne ligands on a metal center
Authors: Mayr Andreas , Bastos Cecilia M. , Daubenspeck Nancy , McDermott Gregory A.
Published: July 2007

Reaction of the alkylidyne complexes [W(CR)Br(CO)3L] [2b (L = CO; R = C6H4‐OMe‐4), 2c (L = CO, R = C6H4‐NMe2‐4), 3a (L = PPh3; R = Ph), and 3c (L = PPh3; R = C6H4‐NMe2‐4)] with methyllithium in THF at ‐78°C affords the alkylidyne acyl tungsten complexes Li[W(CR)(COMe)Br(CO)3L] [4b (L = CO; R = C6H4‐OMe‐4), 4c (L = CO, R = C6H4‐NMe2‐4), 5a (L = PPh3; R = Ph), and 5c (L = PPh3; R = C6H4‐NMe2‐4)]. Reaction of complexes 4 and 5 with C2O2Br2 at ‐78°C‐0°C in CH2Cl2 followed by addition of PPh3 gives the alkyne complexes [WBr2(CO)(CH3C = CR)(PPh3)2] (6). The formation of the alkyne ligands in complexes 6 may be considered as the result of formal coupling of two alkylidyne ligands.
Enol cation radicals in solution, 3[1] Reaction of enol cation radicals in the presence of nucleophiles
Authors: Schmittel Michael , Röck Maik
Published: July 2007

The one‐electron oxidation chemistry of three diaryl‐substituted enols, 1,1‐dimesityl‐1‐propen‐2‐ol (7), 1,2‐dimesityl‐1‐propen‐1‐ol (8), and 2‐mesityl‐2‐phenylethenol (9), has been examined. As a consequence of the pronounced steric shielding around the β‐carbon, 7 does not react with nucleophiles upon addition of 2 eq. of oxidant, but cyclizes to yield benzofuran 18. Under identical conditions, the less shielded enols 8 and 9 react with methanol and other nucleophiles. Several mechanistic hypotheses for nucleophile incorporation are tested, thus allowing the second part of the α‐umpolung reaction of ketones via enol cation radicals to be elucidated mechanistically. Fast‐scan cyclic voltammetry studies (2000 V · s‐1) show no reversible wave of the enol cation radicals. The corresponding methyl enol ether cation radicals, however, have a lifetime of several seconds at ‐10°C, and the kinetics of their reactions with acetonitrile and methanol was probed. The results obtained are consistent with fast deprotonation being the primary reaction of enol cation radicals. Under the given oxidative conditions the radicals formed are further oxidized. Consequently one‐electron oxidation of enols provides an interesting entry to α‐carbonyl carbocation chemistry.
Folgereaktionen von Sulfenen aus Sulfonylchloriden und tertiären Aminen, 3[1,2] Kristallstrukturanalyse von Bis(trimethylammoniosulfonyl)methanid‐tetraphenylborat. – n‐σ*‐Wechselwirkungen (Hyperkonjugation und Homohyperkonjugation) in Sulfen–Amin‐S,N‐Addukten
Authors: Opitz Günter , Wiehn Walter , Ziegler† Manfred L. , Nuber Bernhard
Published: July 2007

Secondary Reactions of Sulfenes from Sulfonyl Chlorides and Tertiary Amines, 3[1,2]. – Crystal Structure Analysis of Bis(trimethylammoniosulfonyl)methanide Tetraphenylborate. – n‐σ*‐Interactions (Hyperconjugation and Homohyperconjugation) in Sulfene – Amine S,N‐Adducts

Bis(trimethylammoniosulfonyl)methanide chloride (3b) could be obtained in 97% yield by reaction of methanedisulfonyl dichloride (5) with three equivalents of trimethylamine. X‐ray analysis of the tetraphenylborate 3c reveals that the conformation of the cation is determined by nC‐σ*S–N interactions (negative hyperconjugation) and by nC‐σ*N–C interactions (negative homohyperconjugation). These effects were deduced from alterations of the bond lengths within the S–N–C chains which are coplanar to the occupied pz orbital at the central C atom. Comparison with known crystal structure data shows, that sulfene – amine S,N‐adducts generally have the zwitterionic ammoniosulfonylmethanide structure 3, stabilized by nC‐σ* interactions.
Organische Synthesen mit Übergangsmetall‐Komplexen, 59[1] Cyclobutanimine aus Carbenchrom‐ oder ‐wolfram‐Komplexen, Isocyaniden und Alkenen durch [2 + 2]‐Cycloadditionen intermediärer Ketenimin‐Komplexe; Liganden‐Abspaltung mit Pyridin
Authors: Aumann Rudolf , Krüger Carl , Goddard Richard
Published: July 2007

Organic Syntheses via Transition Metal Complexes, 59[1]. – Cyclobutanimines from Carbenechromium or ‐tungsten Complexes, Isocyanides, and Alkenes by [2 + 2]‐Cycloaddition Reactions of Ketenimine Complexes; Ligand Disengagement with Pyridine

10‐Iminotricyclo[5.3.0.02,9]deca‐3,5‐diene complexes syn/anti‐4 are obtained in yields higher than 90% by the addition of isocyanides RNC 2 [R = c‐C6H11 (a), CH3 (b)] to (cycloheptatrien‐1‐ylmethyl)carbene complexes LnM=C(OEt)CH2(C7H7) 1 [LnM = Cr(CO)5 (a), W(CO)5 (b)]. The reactions involve an intermediate formation of ketenimine complexes LnM[RN=C=C(OEt)CH2C7H7] 3 by the insertion of 2 into the M=C bonds of 1. Complexes 3 isomerize to give the cyclo‐butanimines 4 by an intramolecular [2s + 2a]‐cycloaddition reaction of the ketenimine to the alkene unit. The structure of anti‐4c has been determined by a crystal structure analysis. Complexes 4 react with pyridine by the fragmentation of the four‐membered ring to yield a tetrahydroazulen‐1‐imine 6 which was hydrolyzed to the corresponding ketone 7;7 is also obtained along an independent route by the photolysis of 1a in the presence of carbon monoxide. The first isolated product of the latter reaction is the tricyclo[5.3.0.02,9]deca‐3,5‐dienone 9, which presumably is formed via an intermediate ketene complex N and the tricyclic ketone O; 9 on warming with pyridine rearranges to 7.
Nitrile Addition to (η4‐Butadiene)zirconocene: The Formation of Organometallic and Metal‐Free Hexatrienediamine Derivatives
Authors: Erker Gerhard , Pfaff Ronald , Krüger Carl , Nolte Matthias , Goddard Richard
Published: July 2007

(η4‐Butadiene)zirconocene adds one equivalent of benzonitrile to form the five‐membered azazirconacyclopentene derivative 7, which contains an NH group in the ring and a vinyl substituent at the α‐carbon center. The reaction of 7 with an additional equivalent of benzonitrile furnishes the chiral nine‐membered metallacycle (magnified image) (12) which may be isomerized to the thermo‐dynamically favored tautomer (magnified image) (13). The Gibbs activation energy of the enantiomerization of the trans‐cycloalkene‐like 13 is ΔG#(323 K) = 15.5 ± 0.3 kcal mol‐1. The analogous conformational equilibration of 12 has a lower activation barrier of ΔG# (236 K) = 12.1 ± 0.3 kcal mol‐1; complex 13 is characterized by X‐ray diffraction. Hydrolysis of 13 yields the conjugated 1,6‐diamino‐1,6‐diphenylhexatriene 16 which is characterized by X‐ray diffraction.
The Pagodane Route to Dodecahedranes Directed Conversions – The Pagodane → Bissecododecahedradiene Stage
Authors: Fessner Wolf‐Dieter , Murty Bulusu A. R. C. , Spurr Paul R. , Pinkos Rolf , Melder Johann‐Peter , Fritz Hans , Prinzbach Horst
Published: July 2007

Three conceptual routes (A, B, C) from [1.1.1.1]pagodane (1) to pentagonal dodecahedrane (2) are evaluated by MM2 (MM3) calculations. After limited experimental success with a catalytic one‐pot route (A), a more selective transformation along one of two stepwise routes (B/C) is explored. An expeditious entry into route C is achieved by hydrogenolytic cyclobutane opening in 1; secopagodane 7 (100%), however, resists both progression along route C (dehydrogenative C—C bond formation to isododecahedrane 8) and crossover into route B (hydrogenolysis to bissecododecahedrane 5). The first transformation along route B, the 2sigma;→2π‐isomerization of the highly strained 1 to bissedodecahedra‐1,10(11)‐diene 3, is not attainable by metal catalysis and cannot productively be brought about by thermal activation: The necessarily very high reaction temperatures (> 700°C) enforce instead a mechanistically interesting fragmentation into two C10H10 halves to give ultimately naphthalene. The very rapid pagodane opening occurring after one‐electron oxidation, too, is not a preparatively useful alternative. Highly efficient, on the other hand, is a two‐step process affording a high yield of the product and consisting of regiospecific, photochemically induced bromine addition to the central four‐membered ring (→ dibromosecopagodane 37) followed by reductive bromine elimination (→ diene 3). In spite of the necessarily rather severe reaction conditions in both steps, this procedure is applicable to the preparation of various 3,8‐difunctionalized bissecodienes (dienedione 11, diene diesters 43, 50, 52, dichlorodiene 56). Limitations of this procedure are met with the 4,4,9,9‐tetrachloropagodane 60 (inert) and the [2.2.1.1]pagodane 80 (bridgehead bromination). The lateral half‐cages of the (seco)‐pagodane structures are explored for preparatively (dis)advantageous steric effects, that might be later exploited on the way towards functionalized dodecahedrane derivatives.
Reaktionen koordinierter Liganden, XVIII. Templatsynthesen und Peripheriereaktionen makrocyclischer Multiphosphanliganden mit funktionellen Gruppen
Authors: Brauer David J. , Dörrenbach Frank , Lebbe Thomas , Stelzer Othmar
Published: July 2007

Reactions of Coordinated Ligands, XVIII. – Template Syntheses and Periphery Reactions of Macrocyclic Multiphosphane Ligands with Functional Groups

Cyclisation of the tridentate phosphanes PhP([CH2]3PRH)2 (R = H, Me) with the divinyl components R′P(CHCH2)2 [R′ = Ph, NEt2, O(iPr)] within Ni(II) templates affords complexes NiBr2L (3a–f) of functionalised macrocyclic tetraphosphanes (L) in almost quantitative yields. An X‐ray structural analysis of the cyano complex [Ni(CN)L]PF6 (5a), obtained by metathetical reactions, reveals a folded 14‐membered macrocyclic ligand L. The P atoms occupy axial and equatorial positions within the trigonal‐bipyramidal ligand arrangement with an equatorial CN group. By periphery reactions at the P–NEt2 function of the 14‐membered ring system POH, PO−, PCl, POR″ derivatives (R″ = Me, iPr, CH2CHCH2) are formed. Addition of methyl acrylate to the PH functions in 3d and 3f leads to macrocyclic diesters 12a, 12b. By cleavage of the PN bond in 3a with concentrated aqueous HBr a complex of composition 7a · HBr · 3 H2O is obtained. An X‐ray structural analysis of the latter shows a POH functionalised macrocyclic tetraphosphane occupying the four basal positions within a square pyramidal coordination geometry at Ni(II).
Derivate des Borols, XVIII. Tricarbonyl[η5‐(1‐phenylborol)]eisen: Zur Reaktivität der koordinierten Liganden
Authors: Herberich Gerhard E. , Carstensen Tobias , Klaff Norbert , Neuschütz Mark
Published: July 2007

Derivatives of Borole, XVIII. – Tricarbonyl[η5‐(1‐phenylborole)]iron: Reactivity of the Coordinated Ligands

The borole complex (C4H4BPh)Fe(CO)3 (1) undergoes Friedel‐Crafts acetylation (MeCOCl/AlCl3) at the meta‐position of the phenyl substituent while the derivatives (C4H4BPh)Fe(CO)2L (3, a: L = NMe3′ b: L = PMe3) are acetylated at the 2‐position of the borole ring. Organolithium reagents (LiMe, LiBu) add to 1 at the boron atom below – 50°C while nucleophilic attack at the carbonyl C atom takes place at higher temperature with formation of acyl anions [(C4H4BPh)Fe(CO)2(COR)]− (6a,b−). The Fischer carbene complex (C4H4BPh)Fe(CO)2[C(OMe)Me] (7) is obtained from 6a−/[Me3O]BF4. Complex 1 reacts with LiN(SiMe3)2 to give [(C4H4BPh)Fe(CO)2(CN)]− (8−) and with 5 M NaOH/C6H6/NBu4HSO4 to produce the hydride NBu4‐[(C4H4BPh)FeH(CO)2] (NBu4 · 9). A highly reactive dianion [(C4H4BPh)Fe(CO)2]2− (102−) is obtained by deprotonation of 9− or by reduction of 1 or 3a in THF at −70°C. Treatment of 102− with Ph3SnCl gives [(C4H4BPh)Fe(CO)2(SnPh3)]− (11−) which is isolated as NEt4 · 11. Slow reduction of 3a with sodium amalgam in THF at −30°C produces doubly CO‐bridged cis‐[{(C4H4BPh)Fe(CO)2}2]2− (122−) which is protonated to the μ2‐hydrido anion [μ‐H‐{(C4H4BPh)Fe(CO)2}2]− (13−).
Amidoxim‐Nachbargruppen in Cyclodehydrierungsreaktionen
Authors: Möhrle Hans , Lessel Jürgen
Published: July 2007

Amide Oxime Functions as Neighbouring Groups in Cyclodehydrogenation Reactions

Dehydrogenation of the o‐(tertiary amino)benzamide oximes 4, which are monosubstituted at the amide N atom of the neighbouring group, by the mercury edta complex yields tricyclic amino nitrones 9 with a quinazoline 3‐oxide moiety or lactams 8. Product formation depends on the nature of the N substituent, the size of the amine ring, and the reaction conditions. The configuration of the amide oximes and the conformation of the tricyclic systems is determined by NMR‐spectroscopic methods.
Regiochemistry of the Intramolecular [2 + 2] Photocycloaddition of Enones to Vinyl Ethers as a Function of Chain Length
Authors: Gleiter Rolf , Fischer Evelyn
Published: July 2007

The intramolecular [2 + 2] cycloaddition of a cyclohexenone moiety bound to a vinyl ether fragment has been explored. The regiochemistry and the quantum yield of the reaction have been investigated as a function of the chain length n and the position of the methoxy group. It has been found that in those cases where the chain consists of three and four members the position of the methoxy group has no influence on the regiochemistry but on the quantum yield. Only head‐to‐head cycloaddition is observed. In the case of n = 2 both the regiochemistry and the quantum yield depend strongly on the position of the methoxy group. It is concluded that the main reason for the different behavior of n = 2 is due to a through‐bond effect between the two olefinic units mediated by a C2H4 bridge.
Imidazole Derivatives, VII. Reaction of 1‐Acylimidazoles with Dialkyl Acetylenedicarboxylates: Synthesis of Imidazo[1,2‐a]pyridines, (2‐Imidazolyl)maleates, 1,5‐Dihydroimidazo[1,2‐a]pyridines, Furo[2′,3′: 2,3]pyrrolo[1,2‐a]imidazoles, Furo[2′,3′: 2,3]pyrrolo[1,2‐a]benzimidazoles and 7H‐Pyrrolo[1,2‐a]imidazoles
Authors: Knölker Hans‐Joachim , Boese Roland , Döring Detlev , El‐Ahl Abdel‐Aziz , Hitzemann Rainer , Jones Peter G.
Published: July 2007

The reaction of 1‐acylimidazoles with dialkyl acetylenedicar‐boxylates provides novel functionalized imidazole derivatives by a sequence of electrophilic attack on the imidazole azine nitrogen atom and subsequent transprotonations and trans‐acylations of the ylide generated in the first step. Based on this methodology we described a condensation of 1‐arylacetylimid‐azoles with DMAD in acetonitrile providing imidazo[1,2‐a]pyridines. We have now achieved a control of the cyclization mode leading to a different ring system simply by varying the acyl side chain. Solvent and reaction temperature influence these cyclizations strongly, thus allowing the preparation of further novel imidazole derivatives including the hitherto unknown furo[2′,3′:2,3]pyrrolo[1,2‐a]imidazole framework. Changing the parameters of the reaction of 1‐alkanoylimidazoles with electron‐deficient acetylenes allows the synthesis of (2‐imidazolyl)maleates 1,5‐dihydroimidazo[1,2‐a]pyridines, furo[2′,3′:2,3]pyrrolo[1,2‐a]imidazoles, furo[2′,3′: 2,3]pyrrolo[1,2‐a]benzimidazoles, and 7H‐pyrrolo[1,2‐a]imidazoles. The crystal structures of compounds 14a, 26, and 31d have been determined by X‐ray analysis.
Diallenylborane als Edukte für Borheterocyclen
Authors: Enders Markus , Pritzkow Hans , Siebert Walter
Published: July 2007

Diallenylboranes as Starting Molecules for Boron Heterocycles

The reaction of allenyllithium with chloro(dialkylamino)bornanes leads to the diallenylboranes 1, 2a, 3a, b, and 4 in 58–80% yield. Attempts to obtain the B‐tert‐butyl derivative 2b resulted in the formation of the unusual bicyclo compound 9. Heating of 1 in toluene gives the intermediate borole derivative 5, which dimerises to the Diels‐Alder product 5′. Reaction of 1 with (C5H5)Co(C2H4)2 leads to the cobalt‐borole complex 6. No 1,5‐H shift occurs on heating 2a and 3, respectively. Heating of 4 in mesitylene yields the dibora tricyclus 7, which undergoes a photochemical 1,5‐H shift to 8. Single crystal X‐ray structure determinations of 7, 8, and the complex 6 confirm their constitutions.
Radikalreaktionen an N‐Heterocyclen, X. Radikalreaktionen cyclischer 1,2‐Diacylhydrazine
Authors: Kluge Ralph , Schulz Manfred , Omelka Ladislav , Reinhardt Michael
Published: July 2007

Free Radical Reactions of N‐Heterocyclic Compounds, X[1]. – Radical Reactions of Cyclic 1,2‐Diacylhydrazines

Cyclic 1,2‐diacylhydrazyls 3 have been detected by ESR spectroscopy during oxidation of the corresponding NH compounds 2. The N coupling constants are determined and confirmed by simulation and by 15N labeling. The hydrazyls 3 react by dimerization to the corresponding tetrazanes of type 5 or by β scission to the diacyl azo compounds 4 and C radicals. The β scission of the radicals 3 is elucidated by UV/Vis detection of the azo compound 4b and reaction of 4b to Diels‐Alder adducts. The alkyl radicals are trapped by nitrosobenzene (8) (ESR).
Photoextrusion von molekularem Stickstoff aus 5‐Alkyliden‐4,5‐dihydro‐1H‐tetrazolen mit Vinyl‐ oder Phenyl‐Substituenten. (E)‐Aziridinimine und neuartige Produkte
Authors: Quast Helmut , Hergenröther Thomas
Published: July 2007

Photoextrusion of Molecular Nitrogen from 5‐Alkylidene‐4,5‐dihydro‐1H‐tetrazoles Substituted by Vinyl or Phenyl Groups. (E)‐Aziridinimines and Novel Products[1]

Direct irradiation of deuterated hydrocarbon solutions of the alkylidenedihydrotetrazoles 11 affords quantitative yields of the aziridinimines (E)‐ and (Z)‐12, besides molecular nitrogen, with (E)/(Z) ratios ranging from 95:5 (12e, ‐40°C) to >99:<1 (12 c, 20°C). From 14, which carries two different groups at the nitrogen atoms, equal amounts of the isomers 13 and 15 are obtained, again with a strong predominance of the (E) diastereomers. The structures of the aziridinimines have been elucidated by their NMR spectra and, in the case of 13 and 15, by [2 + 1] photocycloreversion into the corresponding isocyanides 16 and imines 17, which is induced by selective irradiations with light of shorter wavelengths. Photolysis of the alkenlidenedihydrotetrazole 18c at ‐40°c affords the 2‐imino‐3‐vinylaziridine 20c which decomposes at higher temperatures. Irradiation of 18c at 20°C or partial photolysis at ‐40°C followed by warming to 20°C furnishes the spirocyclic product 19c. The analogous products 19a and b are obtained from 18a and b. The vinyl compound 19a very slowly isomerizes to the ethylidene compound 23 by a proton 1,3‐shift. The spirocyclic structures 19 and 23 are based on mass and NMR spectra including 1H,1H and 13C1H COSY and extensive 1,1H decoupling experiments. The formation of the spirocycles 19 is interpreted in terms of a photoextrusion of molecular nitrogen from 18 to afford 3‐vinylaziridinimines 20 which, at higher temperatures, rearrange to the 1,3‐diazabutadienes 24 by a hydrogen homo[1,5]‐ or homo[1,7]‐shift. [4 + 2] Cycloaddition of 24 to unchanged 18 eventually yields the spirocycles 19.
Photoreactions of Enones with Amines – Cyclization of Unsaturated Enones and Reductive Ring Opening by Photoinduced Electron Transfer (PET)
Authors: Mattay Jochen , Banning Anja , Bischof Eric W. , Heidbreder Andreas , Runsink Jan
Published: July 2007

Photolysis of the unsaturated enones 1 yields [2 + 2] cycloaddition products 2 and 3 with varying regioselectivity. Under electron‐transfer conditions (PET) spirocyclic products 4 are formed. The straight [2 + 2] cycloaddition products 2b,c,f are converted to the spirocyclic products 4b,c,f under the same reaction conditions. The cyclobutane 5 and the cyclopropane 11 also undergo this new reductive ring opening reaction, while the stabilized system 7 is converted to reduced ringenlarged triquinane 10 which may be interesting in natural product synthesis. – Irradiation of 2‐cyclohexen‐1‐one (14) in the presence of N,N‐dimethylallylamine (15) leads to the decahydroisoquinoline 18. A mechanism involving radical intermediates is discussed.
Pinzettenförmige Kohlenwasserstoffe
Authors: Vögtle Fritz , Koch Herbert , Rissanen Kari
Published: July 2007

Tweezer‐Shaped Hydrocarbons

1,8‐Bis[(arylethynyl)phenyl]‐ and ‐[(arylethenyl)phenyl]anthracenes of type I (e.g. 9, 6a) and 1,8‐bis{[(arylethynyl)phenyl]‐ethynyl}‐ and ‐{[(arylethenyl)phenyl]ethynyl}anthracenes of type II (e.g. 16, 13) were synthesized for the first time. Their hydrocarbon framework is formed by Grignard coupling and by Hagihara coupling, respectively. An X‐ray analysis of 13 exhibits an approximate planar skeleton, only one aromatic ring showing a considerable deviation from that plane (Figure 2). The UV and fluorescence properties are discussed. In spite of their preorganized and rather rigid tweezer‐shape the new hydrocarbons do not seem to use their multiple bonds for the cooperative binding of transition metal cations.
1,2:9,10:16,17‐Triethano[23](1,3,5)cyclophanes; Paddlanes with Cyclophane Shaft and Cyclobutane Blades
Authors: Wada Yasuhiro , Ishimura Takayuki , Nishimura Jun
Published: July 2007

The symmetrical and unsymmetrical title compounds 3 and 4 were prepared by intermolecular photocycloaddition of 1,3,5‐trivinylbenzene in 1% yield. The ratio of symmetrical and unsymmetrical paddlanes was 24:76, i.e. nearly a statistical one.
Neue extrem deformierte (Biphenylen‐)Kohlenwasserstoff‐Gerüste
Authors: Schulz Jochen E. , Rissanen Kari , Vögtle Fritz
Published: July 2007

New Extremely Deformed (Biphenylene)Hydrocarbon Skeletons

The tetracyclic carbon skeleton 2‐oxo[3](1,8)biphenylenophane (4) was synthesized by cyclization of a mixture of the bis(bromomethyl) compounds 7a, b with p‐tolylsulfonylmethyl isocyanide. 2‐Hydroxy[3](1,8)biphenylenophane (5) and the [3](1,8)biphenylenophane hydrocarbon 6 were obtained by reduction of 4 with LiAlH4 and NaBH4, respectively. X‐ray analyses of 4 and 6 illustrate the dramatic deformation of bond lengths and angles in these molecules.
Inter‐ and intramolecular hetero diels‐alder reactions, 40. Effect of high pressure on the stereoselectivity of intermolecular hetero diels‐alder reactions
Authors: Tietze Lutz F. , Hübsch Thomas , Oelze Jens , Ott Christian , Tost Winfried , Wörner Gabriele , Buback Michael
Published: July 2007

The hetero Diels‐Alder reaction of enamino ketone 1 with the vinyl ethers 7–11 leading to the dihydropyrans 12a–e and 13a–e is studied in dichloromethane under high pressures up to 7 kbar. The kinetics is measured by on‐line FT‐IR spectroscopy up to 3 kbar. For the first time individual rate coefficients kcis and ktrans have been determined. Pressure‐averaged activation volumes, magnified image, for the overall reaction leading to the formation of the two diastereomers in dichloromethane solution between ‐(19.1 ± 1.7) and ‐(25.4 ± 1.6) cm3 mol−1 are measured. The corresponding activation enthalpies, ΔH‡, are between (62.2 ± 1.6) and (76.3 ± 3.6) kJ mol−1. The cycloaddition shows a remarkable increase in diastereoselectivity in favour of the cis adducts 12a–e toward higher pressure. The pressure‐averaged differences in activation volume, magnified image, for the two reaction pathways leading to cis and trans diastereomers are found to be between ‐(4.5 ± 0.3) and ‐(6.9 ± 0.7) cm3 mol−1. The corresponding differences in activation enthalpy, δδH≠, are between ‐(4.7 ± 1.4) and ‐(9.9 ± 1.6) kJ mol−1. Combination of the overall rate coefficient k = kcis + ktrans for the reaction leading to the two diastereomers with the measured product ratio, ccis/ctrans, which is identified with the ratio of the rate coefficients kcis/ktrans, yields the individual coefficients kcis and ktrans. The rate coefficient kcis is strongly influenced by the steric demand of the substituents on both diene and dienophile whereas ktrans varies to a smaller extent, and the observed changes appear to be mainly due to the electronic properties of the substituents.
α‐Oxygen‐Substituted Organolithium Compounds and Their Carbenoid Nature: Calculations of the Configurational Stability and of LiCH2OH Model Structures, Crystal Structure of Diphenyl(trimethylsilyloxy)methyllithium · 3 THF, and the Stereochemistry of the (Reverse) Brook Rearrangement
Authors: Boche Gernot , Opel Achim , Marsch Michael , Harms Klaus , Hallera Friederike , Lohrenz John C. W. , Thümmler Christina , Koch Wolfram
Published: July 2007

The comparatively high configurational stability of α‐oxygen‐substituted organolithium compounds is confirmed by ab initio calculations [MP2/6–311 + + G(d,p)]. Model calculations of the LiCH2OH structures 21A–D (MP2/6–31G(d)//3–21G and MP2/6–311 + + G(d,p)//MP2/6–311 + + G(d,p)) are in agreement with recently determined crystal structures of α‐oxygen‐sub‐stituted organolithium compounds. They also suggested the preparation of a new structural type (21C) which has been verified by means of diphenyl(trimethylsilyloxy)methyllithium · 3 THF (24 · 3 THF) as shown by X‐ray crystallography. The lengthening of the CO bonds in all four α‐oxygen‐sub‐stituted organolithium compounds known to date contrasts strongly with the wealth of structural data from organolithium compounds α‐substituted with “typical” acceptor substituents: on lithiation the carbon‐acceptor bond length in these compounds is always shortened. This difference is in agreement with a carbenoid character of α‐oxygen‐substituted organolithium species. Finally, the crystal structure of 24 · 3 THF serves as a model for the surprising stereochemistry of the (reverse) Brook rearrangement.
Photoinduced electron transfer in porphyrin‐quinone cyclophanes, 5. Quinone‐porphyrin‐quinone and quinone‐porphyrin‐donor cyclophanes: Syntheses, structures and electron‐transfer‐related properties
Authors: Staab Heinz A. , Weiser Jürgen , Baumann Ernst
Published: July 2007

To study the structure dependence of photoinduced electron transfer between porphyrins and quinones the concept of a new family of porphyrin‐quinone cyclophanes with vertical arrangements of porphyrin and quinone units is presented. The syntheses of the quinone‐porphyrin‐quinone cyclophane 1, the prototype of this series, and of the quinone‐porphyrindonor cyclophanes 12 and 14 are described. Spectroscopic data are discussed with regard to the structures involved and in relation to electron‐transfer reactions occurring in these systems.
Photodecarbonylation of 2(3H)‐thiophenones
Authors: Hinrichs Heiko , Margaretha Paul
Published: July 2007

Light‐induced (300 nm) loss of CO converts 2(3H)‐thiophenones to either thietes, thiophenes, homothiophenes, or thiopyrans, the product distribution being strongly influenced by the alkyl substitution pattern on the thiolactone.
Cobaltkomplexe mit As4‐Liganden
Authors: Scherer Otto J. , Pfeiffer Karl , Wolmershäuser Gotthelf
Published: July 2007

Cobalt Complexes with As4 Ligands

The reaction of [Cp*Co(μ‐CO)]2(Co = Co) (1) with As4 in boiling toluene gives the cobalt complexes [Cp*Co(CO)(η1:1‐As4)] (2), [{Cp*Co(CO)}2(μ‐η1:1:1:1‐As4)] (3), exo,endo‐[Cp*Co(μ‐η4:1:1‐As4)Co(CO)Cp*] (4a, b), and [Cp*Co(μ‐η2:2‐As2)]2 (5), Cp* = C5Me5. 2,3, and 4b have been characterized by X‐ray structure analyses. With respect to the mechanism of this reaction the successive cleavage of two, three, and four As–As bonds of yellow arsenic, As4, has been proved.
Chiral Epoxides as Building Blocks for Ethylene‐Bridged ansa‐Metallocene Complexes – Synthesis of C1‐Symmetrical Zirconocene Dichlorides with Two Different Cyclopentadienyl Units
Authors: Rieger Bernhard , Steimann Manfred , Fawzi Riad
Published: July 2007

Epoxystyrene undergoes ring opening on treatment with tetraphenylcyclopentadienyl‐ and fluorenyllithium to give the corresponding chiral alcohols 3 and 4 in high yield. Their trifluoromethanesulfonate derivatives 5 react with one equivalent of cyclopentadienylsodium to form the ligand precursors 1‐cyclopentadienyl‐1‐phenyl‐2‐(tetraphenylcyclopentadienyl)ethane (L1H2) and 1‐cyclopentadienyl‐2‐(9‐fluorenyl)‐1‐phenylethane (L2H2). The zirconocenes L1ZrCl2 (7a) and L2ZrCl2 (7b) are prepared from the dilithio salts L1Li2 and L2Li2, respectively. A low‐temperature X‐ray structure investigation of complex 7a demonstrates the chiral arrangement of the four phenyl substituents of the tetraphenylcyclopentadienyl (C5Ph4) unit. A 1H‐NMR study shows that the phenyl groups rotate rapidly on the NMR time scale at room temperature. The dependence of phenyl rotation on temperature is discussed.
Alkylsilber‐ und Alkylgold‐Reagenzien, II. Cyano(methyl)argentate: Spektroskopie, Selektivität als Methylierungsreagenzien, Vergleich mit anderen Methylsilber‐Reagenzien
Authors: Kauffmann Thomas , Neiteler Christel , Robbe Sonja
Published: July 2007

Alkylsilver and Alkylgold Reagents, II[1]. – Cyano(methyl)argentates: Spectroscopy, Selectivity as Methylating Reagents, Comparison with Other Methylsilver ReagentsAs the first examples of a new type of Ag complex the cyanoargentates MeAg(CN)Li (1), Me2Ag(CN)Li2(2), MeAg‐(CN)MgBr (3), and Me2Ag(CN)(MgBr)2(4) were prepared in solution or suspension by transmetallation of MeLi or MeMgBr with AgCN. Compared to AgBr‐derived reagents, such as MeAg · MgBr2(5) and Me2AgMgBr (6), the cyano(methyl)‐argentates are clearly less sensitive to light. According to the IR spectrum, the Ag atom of2is connected with the cyano group. The13C‐NMR spectra of2, 4, 5, and6furnish proof of the Ag – Me group in these compounds and points to the partial structure Ag – Me – Mg in4, 5, and6. – Complexes2(stable up to 20°C),4, 5, and6methylate the ketoaldehyde13with high selectivity at the aldehyde group (best yield with4). 4, 5, and6exhibit high cheleselectivity in the reaction with the hydroxy diketone22(best yield with4) and comparable intermolecular competitive systems.2and6methylate 11,12‐epoxy‐2‐deodecanone (28) with virtually complete regioselective ring opening to give 11‐hydroxy‐2‐tridecanone (29). In contrast to Me2Cu(CN)Li2(7) and Me2CuMgBr, the analogous reagents Me2Ag(CN)Li2(2) and Me2AgMgBr (6) methylate styrene oxide (32), and6also methylates α‐methylstyrene oxide (36) in α‐position to the phenyl residue with high selectivity, yielding nearly exclusively 2‐phenylpropanol (33) or 2‐methyl‐2‐phenylpropanol (37), respectively. The selective „α attack„ of Ag reagents is explained by fixation of the reagent to the phenyl residue of32and36in the first reaction step.
The Mechanistic Diversity of the Thermal and Photochemical Decomposition of Bis(phenylphosphonoyl)Peroxides: Concerted Polar, Homolytic, and Electron‐Transfer Processes On the Reactivity of (Phenylphosphonoyl)oxyl Radicals
Authors: Korth Hans‐Gert , Lommes Petra
Published: July 2007

The thermal and photochemical decomposition of the first bis(phenylphosphonoyl)peroxides, dioxybis[(n‐butoxy)phenyl‐phosphane oxide] (5), and dioxybis[(phenoxy)phenylphosphane oxide] (6) has been studied in various solvents by 1H‐, 13C‐, and 31P‐NMR spectroscopy, laser flash photolysis (LFP), and ESR spin‐trapping experiments. Kinetic studies reveal at 20°C a ca. 270 times slower thermal decay for 5 than for 6, which primarily results from a lower A factor rather than differences in the activation energies. The thermal decay of 5 occurs predominantly by a novel, presumably concerted polar rearrangement with formation of a thermally unstable, mixed phosphonoyl‐phosphoryl anhydride. Photolysis of 5 induces homolytical cleavage of the peroxy bond with release of [(n‐butoxy)phenylphosphonoyl]oxyl radicals 7. Radical 7 is characterized by a broad, transient UV/Vis absorption spectrum in the 400 to >700 nm range (λmax ca. 580 nm), as has been demonstrated by 248‐nm LFP of 5 in acetonitrile solution. The short lifetime of this absorption indicates an extremely high reactivity (in hydrogen abstraction and addition) of this electrophilic radical. The thermal and photochemical decomposition of peroxide 6 leads to a virtually identical product distribution, suggesting O–O bond cleavage to be the major initial reaction under both conditions. LFP at 248 and 308 nm of a solution of 6 in acetonitrile initially produces a weak, broad absorption at ca. 500 nm and stronger bands at 280 and 400 nm. The highly transient 500‐nm absorption is assigned to the [(phenoxy)phenylphosphonoyl]oxyl radical 8, the other bands are attributed to the phosphonoyloxy‐substituted benzene radical cation 8Z. The formation of this species can be explained in terms of electron transfer in the first‐formed oxyl radical 8 and/or the intact peroxide 6, followed by cleavage of the peroxy bond. The decay of 8Z is accompanied by the build‐up of the absorption spectrum of a 1,4‐dioxy‐substituted biphenyl radical cation.
Medium‐Sized Cyclophanes, 20. Synthesis and Conformational Studies of syn‐ and anti‐Dihydroxy[n.2]metacyclophanes
Authors: Yamato Takehiko , Matsumoto Jun‐Ichi , Tokuhisa Kiwamu , Kajihara Masami , Suehiro Kazuaki , Tashiro Masashi
Published: July 2007

syn‐ and anti‐Dimethoxy[n.2]metacyclophanes 9 are obtained by pyrolysis of the corresponding anti‐sulfones 8, which are prepared by the reaction of 1,n‐bis[3‐(chloromethyl)‐2‐methoxyphenyl]alkanes 6 with Na2S in ethanol under the high dilution conditions, followed by the oxidation of the obtained thiametacyclophanes 7 with m‐chloroperbenzoic acid. Demethylation of anti‐dimethoxy[n.2]metacyclophanes anti‐9 with BBr3 in dichloromethane affords the corresponding anti‐dihydroxy[n.2]metacyclophanes anti‐10. On the other hand, demethylation of syn‐dimethoxy[3.2]‐syn‐ 9b and ‐[4.2]meta‐cyclophane syn‐9c gives syn‐dihydroxy[n.2]metacyclophanes syn‐10b, c, but syn‐dimethoxy[5.2]‐syn‐9d and ‐[6.2]metacyclophane syn‐9e are converted into the corresponding anti‐dihydroxy[n.2]metacyclophanes anti‐10d, e. AlCl3 · CH3NO2‐catalyzed de‐tert‐butylation of tert‐butyl‐syn‐ and ‐anti‐dihydroxy[3.2]‐ and ‐[4.2]metacyclophanes syn/anti‐10b, c has been carried out in benzene to give the desired metacyclophanes anti‐11a–c and syn‐11c except syn‐dihydroxy‐[3.2]metacyclophane syn‐11b which is converted into 8,17‐epoxy[3.2]metacyclophane 13. The assignment of syn and anti conformations has been confirmed by 1H‐NMR analyses and X‐ray diffraction studies. The dynamics of the ring inversion and UV spectra are also discussed.
Synthese und Komplexbildung eines neuen makrocyclischen Liganden mit drei Benzimidazolin‐2‐on‐Einheiten
Authors: Weber Edwin , Piel Manfred , Buschmann Hans‐Jürgen , Cleve Ernst
Published: July 2007

Synthesis and Complex Formation of a New Macrocyclic Ligand Incorporating Three Benzimidazolin‐2‐one Units The new macrocyclic ligand 1 composed of three benzimidazolin‐2‐one‐1,3‐diyl and three propane‐1,3‐diyl building blocks has been synthesized. Complex formation constants in water involving Li+, Na+, K+, Mg2+ Ca2+, Si2+, and Ba2+ are discussed. The most stable complex is formed with Ca2+.
Synthese von [n.1.1]Propellanen (n = 2, 3, 4)
Authors: Fuchs Josef , Szeimies Günter
Published: July 2007

A facile access to the parent [n.1.1]propellanes 2, 3 and 4 is presented. Lithiation of methallyl alcohol with the BuLi/TMEDA complex and reaction of the organometallic intermediate 8 with paraformaldehyde, ethylene oxide, or oxetane affords the diols 9 which are converted via the dichlorides 10 into the tetrahalides 11. The cyclization of 11 to the corresponding propellanes is effected with 2 equiv. of MeLi or BuLi via the bromobicyclo[1.1.0]butanes 12. As expected, 2 cannot be isolated; its formation is deduced from the structure of the consecutive products.
Konkave Farbstoffmoleküle vom Triphenylmethan‐Typ
Authors: Berscheid Ralf , Nieger Martin , Vögtle Fritz
Published: July 2007

Concave Triphenylmethane Dyestuffs

Triply‐ and doubly‐bridged as well as dye molecules (2, 18, and 11) connected by a single chain were prepared including the corresponding phenolphthalein and fluorescein derivatives (24a–c). The concave orange‐coloured triphenylmethane dye 2 exhibits solvatochromic and halochromic effects different to nonmacrocyclic reference substances. The triphenylmethane dyes are reversibly transferred to the corresponding uncoloured macrocycles by changing the pH. The structures of 9, 22b, and 22c were confirmed by X‐ray analyses.
Pressure‐Induced Diastereoselectivity in Photochemical [2 + 2] Cycloaddition Reactions
Authors: Buback Michael , Bünger Joachim , Tietze Lutz F.
Published: July 2007

Photochemical [2 + 2] cycloaddition reactions under high pressure of cyclopentenone 1a or cyclohexenone 15, as well as of 1a or 3‐substituted cyclopentenones 1b–d with cyclopentene (2), and of 1b with 3,3‐dimethyl‐1‐butene (18) are described. Whereas the pressure dependence on the regioselectivity in the photoaddition of 1a and 15 is very small, δδV≠ values up to 2.0 ± 0.3 cm3 · mol‐1 have been found for the diastereoselectivity in the reactions of 1a–d with 2 and of 1b with 18.
2,6‐Dimethyl Semibullvalene‐2,6‐dicarboxylates
Authors: Quast Helmut , Witzel Alexander , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von
Published: July 2007

The enolized β‐oxo ester 9 is reduced by NaB(CN)H3 in weakly acidic methanol solution to afford an almost quantitative yield of a mixture of diastereomeric β‐hydroxy esters 10. On treatment with phosphorus oxychloride in pyridine, 10 is converted into a mixture of the β‐chloro esters exo‐11, endo‐11, exo‐12, endo‐12, and 13 which is separated in part by chromatography. Sodium methoxide in methanol eliminates hydrogen chloride from the crude mixture of β‐chloro esters producing the α,β‐unsaturated ester 7a in 84% yield based on 9. – Acid‐catalysed equilibration of the known vinyl sulphides C2‐ and Cs‐15 is carried out on large scale furnishing a 73:27 ratio of C2‐ and Cs‐15. This mixture is oxidized to the sulphones C2‐ and Cs‐16 which are allowed to react with sodium cyanide supported on aluminium oxide affording the α,β‐unsaturated dinitrile 17 which is isolated by chromatography. Thus, 17 is now available on a 30‐g scale. Methanolysis of 17 by a prolonged treatment with hydrogen chloride in methanol followed by hydrolysis of the Pinner salt leads to 7b. – Both α,β‐unsaturated esters 7a and b are readily brominated at the allylic positions by N‐bromosuccinimide to yield the γ,γ′‐dibromo esters 19a and b. Zinc‐copper couple in tetrahydrofuran converts 19a and b into the semibullvalenedicarboxylates 2a and b. While 2a is persistent only in dilute solutions, thus frustrating all attempts at its isolation, 2b exhibits considerable stability in solution and forms lemon‐coloured crystals. The semibullvalenedicarboxylates 2a and b undergo a very rapid degenerate Cope rearrangement in solution. In addition, 2b exhibits reversible thermochromism in both solution and solid state. The structures of the new compounds are based on spectroscopic evidence, including mass, IR, and NMR spectra. The configurations of exo‐11, exo‐12, 19a and b are established by X‐ray diffraction analyses.
Diphenyl‐ and Bis(phenylethynyl)semibullvalenes
Authors: Quast Helmut , Carlsen Jürgen
Published: July 2007

The 2,6‐ (6b, c) and 3,7–substituted 1,5–dimethylbicyclo‐[3.3.0]octadienes C2‐ and Cs‐9b and c are brominated by N‐bromosuccinimide in the allylic positions to afford the dibromides 7b, exo,exo‐7c, 10b and c, respectively. An excess of N‐bromosuccinimide converts 10b into the unsymmetrical tetrabromide 11. On chromatography over silica gel, exo,exo‐7c is epimerized to endo,endo‐7c, while methanolysis occurs on reversed–phase chromatography yielding the dimethoxy compound 8. Under ultrasonic irradiation, the zinc–copper couple converts the bromides 7b, exo,exo‐7c, 10c, and 11 into the semibullvalenes 1b, c, 2c, and 12 which are persistent in dilute solutions when atmospheric oxygen is strictly excluded. The UV/Vis spectra of 1b, c, 2c, and 12 have been recorded during reversed–phase HPLC on a Bruker ChromScan detector. Notwithstanding the absence of a classical chromophor, 1c does absorb at no less than 450 nm.
Transition–Metal–Diene Complexes in Organic Synthesis, 12. Regio‐ and Stereoselectivity of Electrophilic Substitutions of Arylamines by Tricarbonyliron–Complexed Cyclohexadienylium Cations and Oxidative Cyclizations to Carbazoles
Authors: Knölker Hans–Joachim , Bauermeister Michael , Pannek Jörn–Bernd
Published: July 2007

Electrophilic substitutions of donor–substituted arylamines using tricarbonyliron–complexed cyclohexadienylium cations lead regio‐ and stereoselectively to the corresponding tricarbonylcyclohexadieneiron complexes. The C–C bond formations occur regioselectively in the ortho position with respect to the amino group with arylamines containing a substituent in the para position. The initially formed N‐alkylated arylamine (kinetic product) is shown to rearrange in an intermolecular process to the C‐alkylated arylamine (thermodynamic product). The reported oxidative cyclization to 3–methylcarbazole yields large amounts of the demetalated ligand. However, oxidative cyclization to 3–methoxycarbazole is possible under mild reaction conditions (room temperature) by using especially activated manganese dioxides.