bluuebunny/crossref_metadata_2025 huggingface dataset:
η2‐tert‐Butylphosphaacetylen‐Komplexe des Titanocens und Zirkonocens
Authors: Binger Paul , Biedenbach Bruno , Herrmann Albert T. , Langhauser Franz , Betz Peter , Goddard Richard , Krüger Carl
Published: July 2007

η2‐tert‐Butylphosphaacetylene Complexes of Titanocene and Zirconocene

(η2‐2‐tert‐Butyl‐1‐phosphaacetylene)(trimethylphosphane) complexes of titanocene (5a) and zirconocene (5b) are obtained in 85 and 73% yield, resp., by the reaction of 2‐tert‐butyl‐1‐phosphaacetylene (1) with the corresponding bis(trimethylphosphane)metallocenes 2a (MTi) and 2b (MZr). For the preparation of 5b it is more convenient to start with the (1‐butene)zirconocene complex 3 or with the tolanezirconocene complex 4. With the help of a suitable Lewis‐acid, e.g. triethylborane, trimethylphosphane can be eliminated from 5a or 5b to yield the new coordinatively unsaturated phosphaalkyne metallocenes 6a (MTi) and 6b (MZr), which are unstable and oligomerize easily to the dimer 7 (MTi) and trimer 8 (MZr); only the monomer 6a can be observed in solution. The crystal structures of 5a, 7, and 8 are determined by X‐ray analyses.
Functionalized cyclopentadienyl ligands, IV. Synthesis and complexation of linked cyclopentadienyl‐amido ligands
Authors: Okuda Jun
Published: July 2007

[(tert‐Butylamino)dimethylsilyl]cyclopentadienes C5H5‐n‐(CMe3)n(SiMe2NHCMe3) (n1, 2) and C5H4(SiMe3)(SiMe2‐NHCMe3) have been prepared and the complexation of their lithium derivatives with FeCl2(THF)1.5 and TiCl4(THF)2 investigated.
s̀‐Push‐pull substitution in iminophosphanes, a theoretical study
Authors: Schoeller Wolfgang W. , Busch Thilo , Niecke E.
Published: July 2007

A combination of α‐electron‐withdrawing/‐releasing substituents (push‐pull substitution) at iminophosphanes considerably lengthen (shorten) the central PN bond as revealed by ab initio calculations on model geometries; they also stress the importance of the energy barrier to inversion at nitrogen.
Mitteilungen über Metalltrifluorphosphan‐Komplexe, 51. Hexakis(trifluorphosphan)vanadium(0)‐Synthese, Eigenschaften und Reaktionen
Authors: Collong Wilfried , Kruck Thomas
Published: July 2007

Communications on Metal Trifluorophosphine Complexes, 51. – Hexakis(trifluorophosphine)vanadium(0) – Synthesis, Chemical Properties, and Reactions

[Na(diglyme)2][V(PF3)6] reacts with [PhN2][BF4] to afford the highly volatile, paramagnetic compound V(PF3)6 (1), while the reaction with [C7H7][BF4] yields [C7H7][V(PF3)6]. The metallocenium complexes [MCp2][V(PF3)6] (MFe, Co, Ni) are prepared by one‐electron oxidation of MCp2 by 1.
Aza‐crown ethers with quinone side chains: Synthesis, complexation, and protonation
Authors: Ossowski Tadeusz , Schneider Hermann
Published: July 2007

The synthesis and spectroscopic investigation of aza‐crown ethers with anthraquinone‐ and 1‐aminoanthraquinone‐functionalized side chains are described. Cation‐induced shifts in the UV/VIS absorption spectra of the ligands dissolved in propylene carbonate are observed only for Li+ among the alkali metal ions and for Mg2+ among the alkaline earth metal ions as well as for Ag+ and Tl+. Only hypsochromic shifts of the absorption spectra of anthraquinone‐bearing aza‐crown ethers are observed on protonation. The variations of the extinction coefficients are discussed with respect to the sequence of protonation of the different amino groups.
Synthese und Reaktionen Chinuclidin‐stabilisierter Sulfene, R1R2CSO2←N(CH2CH2)3CH
Authors: Sundermeyer Wolfgang , Waldi Joachim
Published: July 2007

Synthesis and Reactions of Quinuclidine‐Stabilized Sulfenes, R1R2CSO2←N(CH2CH2)3CH

Quinuclidine adducts of the sulfenes 3 and 10 have been isolated and have proven to be good sources for investigating the reactivity of the respective sulfenes. Water and some alcohols react with 3 as well as with “disulfene” (5) in the presence of quinuclidine (2) under formation of the corresponding (alkyl)chinuclidinium methanesulfonyl methanesulfonates 6a–f. The expected intermediate mesyl methanesulfonic acid esters could only be isolated in the case of 4. Similar results were obtained on attempted synthesis of methylsulfene. Only the noncyclic dimer 10 could be prepared, which reacts with alcohols or water forming 11a–c. The formation of “monomeric” sulfene or methylsulfene under these conditions could be ruled out by comparison with their expected hydrolysis products 8 and 13, which were synthesized separately.
N‐Aryl‐O‐(α‐aminoacyl)hydroxylamine: Modellreaktionen mit Desoxyguanosin, Guanosin und 5′‐Guanosinmonophosphat zur Aktivierung monocyclischer aromatischer Amine (z. B. Phenacetin) zu ultimaten Carcinogenen
Authors: Meier Chris , Boche Gernot
Published: July 2007

N‐Aryl‐O‐(α‐aminoacyl)hydroxylamine: Model Reactions with Deoxyguanosine, Guanosine and 5′‐Guanosinemonophosphate for the Activation of Monocyclic Aromatic Amines (e.g. Phenacetin) into Ultimate Carcinogens

In in vitro model reactions of the activation of monocyclic aromatic amines by α‐amino acids it is shown that α‐amino‐hydroxamic acids 8 and 9 rearrange base‐catalyzed to N‐(α‐aminoacyloxy)arylamines 10 and 11 which react with bionucleophiles such as deoxyguanosine (dG) (12), guanosine (G) (13) and 5′‐guanosinemonophosphate (5′‐GMP) (14) to form adducts. We describe the regioselective formation of the C‐8 adducts of 4‐chloroaniline (15), aniline (16), 4‐methylaniline (17), and 4‐methoxyaniline (18), respectively, [“N‐(deoxyguanosine‐8‐yl)anilines”], and also of N‐(guanosine‐8‐yl)‐4‐methylaniline (21) and 8‐(4‐methylanilino)‐5′‐guanosinemonophosphate (22). Similar reactions of the N‐(acetoxy)arylamines 20, which are very likely to be “ultimate” carcinogens of aromatic amines, lead to the same C‐8 adducts 15–18, 21, and 22 in comparable yields. These in vitro reactions thus show that the N‐(α‐aminoacyloxy)arylamines 10 and 11 react like the N‐(acetoxy)anilines 20 as “ultimate” carcinogens. Therefore, the activation of aromatic hydroxylamines by O‐α‐aminoacylation is of similar quality as by O‐acetylation.
Transition metal catalyzed oxidations, 3. Reaction of 4‐hydroxy[2.2]paracyclophane with the mimoun molybdenum oxodiperoxo complex [Mo(O2)2O]· Py · HMPT
Authors: Krohn Karsten , Rieger Hagen , Hopf Henning , Barrett David
Published: July 2007

A four‐step preparation of dimethyl 7‐oxobicyclo[2.2.1]‐heptane‐exo‐2, exo‐3‐dicarboxylate (4) in satisfactory yield from the readily available 6,6‐dimethylfulvene and maleic anhydride is described. Compound 4 represents a well‐functionalized intermediate for the synthesis of norbornane derivatives which is used for an improved synthesis of the tricyclic diester 7, precursor of the cage compound 8. An alternative approach to diester 7 from dimethyl 7‐isopropylidenebicyclo[2.2.1]heptane‐exo‐2, exo‐3‐dicarboxylate (2) is also discussed.
Ein neues PH‐funktionelles Diphosphadistannetan: (tBu2SnPH)2
Authors: Hänssgen Dieter , Aldenhoven Heinz , Nieger Martin
Published: July 2007

A Novel PH‐Functional Diphosphadistannetane: (tBu2SnPH)2

The reaction of tBu2SnCl2 with NaPH2 in liquid ammonia yields the four‐membered ring compound (tBu2SnPH)2 (1). The corresponding silyl compound, (tBu2SnPSiMe3)2 (2), is obtained by metallation of 1 with tBuLi and metathesis with Me3SiCL Both compounds are characterized by NMR analysis (1H, 31P, 119Sn) and 1 by an X‐ray structure analysis; it reveals a planar heterocycle.
Organische Synthesen mit Übergangsmetallkomplexen, 46. Alkenylcarben‐Chrom‐ und ‐Wolframkomplexe; Protonierung und Aktivierung durch Elektronen‐ziehende Substituenten
Authors: Aumann Rudolf , Hinterding Peter , Krüger Carl , Betz Peter
Published: July 2007

Organic Syntheses via Transition Metal Complexes, 46. — Alkenylcarbene Chromium and Tungsten Complexes; Proton Addition and Activation by Electron‐Withdrawing Substituents

Alkenylcarbene complexes LnMC(OEt)‐CHC(R)NMe2[1, LnM  Cr(CO)5, W(CO)5; R  H, CH3, C6H5] add HBF4 in ether to give novel cationic carbene complexes [Ln MC(OEt)‐CH2‐C(R)NMe2]BF4 (3) by protonation at C‐2 of the C‐CC ligand. The addition of HBF4 to 7 leads to the formation of the cyclic carbene complexes 8. Structures of 3 and 8 are assigned spectroscopically. X‐ray data are reported for 8a. Protonation of 1 and 7 results in a strong deshielding of the carbene carbon atoms, which parallels an increase of reactivity at the MC bonds. An activation of the MC bond has also been achieved by electron‐withdrawing substituents like N‐acyl groups. We report on the first synthesis of [β‐(acylamino)‐alkenyl]carbene complexes 13, which are more reactive than β‐(aminoalkenyl)carbene complexes 7.
Intra‐ und extraannular funktionalisierte helical‐chirale [2.2]Metacyclophane: Synthese, Circulardichroismus und Struktur‐Chiroptik‐Beziehungen
Authors: Vögtle Fritz , Knops Peter , Ostrowicki Andreas
Published: July 2007

Intra‐ und Extraannularly Functionalized Chiral [2.2]Metacyclophanes: Synthesis, Circular Dichroism, and Structure ‐ Chiroptic Relationships

A simple one‐step cyclization reaction for the synthesis of the title compounds 1‐5 is presented; separation (enrichment) of enantiomers is achieved by HPLC mainly on (+)‐PTrMA. The kinetics of interconversion (racemization) of the new dihetera[2.2]metacyclophanes are determined: No racemization of the internally substituted phanes is found on heating until decomposition, whereas the extraannularly substituted compounds exhibit barriers of interconversion of about 130 kJ/mol, similar to that of the unfunctionalized skeleton 1a. For the pyridinophane 2 the barrier (110 kJ/mol) is lower corresponding to the decreased spatial requirement of the nitrogen lone pair compared to a C‐H bond. The circular dichroism curves of the intraannularly functionalized phanes are compared with those of the extraannularly functionalized reference compounds: A bathochromic shift of the Cotton effect at short wavelengths is found, which is increasing with the bulkiness of the internal functional group.
Struktur und Reaktivität des α,p‐Dimers aus 2,2‐Dimethyl‐1‐(1‐naphthyl)propyl‐Radikalen
Authors: Peyman Anuschirwan , Peters Karl , von Schnering Hans Georg , Rüchardt Christoph
Published: July 2007

Structure and Reactivity of the α,p‐Dimer from 2,2‐Dimethyl‐1‐(1‐naphthyl)propyl Radicals

The title compound 2 formed by recombination of two 2,2‐dimethyl‐1‐(1‐naphthyl)propyl radicals 1, is the first isolated α,p‐dimer from secondary benzyl radicals. 2 is obtained in crystalline form, its structure is determined by X‐ray analysis and compared with the results obtained by MMPI calculations. 2 exhibits unusual reactivity in the presence of acid. Its thermal stability is much higher than that experienced with comparable α,p‐dimers of tertiary benzyl radicals.
Darstellung und Struktur von Alkali‐penta‐tert‐butoxystannaten(IV)
Authors: Veith Michael , Reimers Michael
Published: July 2007

Preparation and Structure of Alkali Penta‐tert‐butoxystannates(IV)

Potassium, rubidium, and caesium tert‐butoxide react with tin tetra‐tert‐butoxide in toluene to form compounds MSn(OtBu)5 [MK(2), Rb (3), Cs (4)] in contrast to lithium and sodium tert‐butoxide. The compounds 2–4 are soluble in non‐coordinating solvents and seem to be almost monomeric. 2 crystallizes as 2 · 1/2 toluene in the orthorhombic space group Fddd. The X‐ray structure determination shows 2 to be coordinated as a helical polymer with the tin atom in the center of a trigonal bipyramid of tert‐butoxide groups interlinked by two structurally different potassium atoms.
9‐Fluor‐9‐borabicyclo[3.3.1]nonan ‐ Charakterisierung in Lösung und im Kristall
Authors: Köster Roland , Schüßler Wilhelm , Boese Roland
Published: July 2007

9‐Fluoro‐9‐borabicyclo[3.3.l]nonane — Characterization in Solution and in the Solid State

9‐Fluoro‐9‐borabicyclo[3.3.1]nonane (1), prepared from bis(9‐borabicyclo[3.3.1]nonane) with SbF3 or SbF5 in high yields, is characterized by IR, mass, and multi‐NMR spectroscopy. Pure 1 in solution has a small 11B‐NMR singlet signal in contrast to the freshly prepared 1 with the normal JPB‐split 11B resonance. The X‐ray structure analysis of 1 with three differently bonded molecules I–III (Abb. 2) in the cell shows a monomer and a dimer of 1 with DFB coordination bond. – Some Lewis base adducts of 1 are prepared, the others were characterized by 11B‐NMR spectra.
Wasserlösliche Metallkomplexe und Katalysatoren, IV. 2,2′‐Bipyridin‐5‐sulfonsäure: Synthese, Reinigung, Derivate und Metallkomplexe
Authors: Herrmann Wolfgang A. , Thiel Werner R. , Kuchler Josef G.
Published: July 2007

Water‐Soluble Metal Complexes and Catalysts, IV. — 2,2′‐Bipyridine‐5‐sulfonic Acid Synthesis, Purification, Derivatives and Metal Complexes

The synthesis of 2,2′‐bipyridine‐5‐sulfonic acid (1a) is achieved by mercury(II)‐catalyzed sulfonation of 2,2′‐bipyridine in oleum (30% SO3) in 10‐50‐g amounts. The crude product is purified by extraction of 1a as tetra(n‐butyl)ammonium salt into dichloromethane and re‐extraction of the free acid with conc, hydrobromic acid. Melting of 1a together with potassium hydroxide gives 5‐hydroxy‐2,2′‐bipyridine (2). The salts 1b–d (Na+, [N(n‐C4H9)4]+, [P(C6H5)4]+) and sulfonamides 1f–h (tert‐butyl, benzyl, 2‐pyridylmethyl) of the acid 1a are ligands of different solubility. The coordination chemistry of these N,N‐chelating ligands is studied. The compounds 4–14 of chromium, molybdenum, tungsten, manganese, rhenium, and osmium containing carbonyl or oxo ligands are prepared as examples of chelate complexes with metals in low and high oxidation states. The solubility of the complexes is mostly determined by the cations: sodium salts are usually soluble in water and/or in short‐chained alcohols. Tetra‐n‐butylammonium and tetraphenylphosphonium salts and the sulfonamides are soluble in polar organic solvents. On the other hand, the distribution of charge has an influence on solubility. Increased polarity of the anion, caused by high oxidation states of the metals, decreases the solubility of the complex in organic solvents.
Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen, LXXXII. Zweikernige μ‐Benzylidin‐Komplexe mit Doppelbindung zwischen Rheniumatomen
Authors: Herrmann Wolfgang A. , Kiprof Paul , Felixberger Josef K.
Published: July 2007

Multiple Bonds Between Main‐Group Elements and Transition Metals, LXXXII. — Dinuclear p‐Benzylidyne Complexes Having a Double Bond between Rhenium Atoms

The dialkylrhenium(V) complex (η5‐C5Me5)Re(O)(CH2Ph)2 (3) reacts with the organotitanium reagents (η5‐C5H5)TiX3 (X  Cl, Br) to yield the dinuclear rhenium(IV) complexes (η5C5Me5)2 Re2X3(CC6H5) (4a, b). According to a single‐crystal X‐ray diffraction analysis, 4a′ (C5Me4Et in place of C5Me5) represents one of the few known examples of μ‐alkylidyne complexes that have metal‐to‐metal multiple bonds. The molecule of C2 symmetry has a planar four‐membered Re,Cl,Re′,C‐ring geometry and two trans‐oriented sets of ligands. Very small angles at the bridging chloro ligand and alkylidyne carbon atom result from the short metal‐metal distance (double bond).
Gold complexes with selenium ligands, I. Preparation and crystal structures of phenylselenolato‐gold(I) complexes
Authors: Jones Peter G. , Thöne Carsten
Published: July 2007

(Triphenylphosphine)phenylselenolatogold(I), Ph3PAuSePh (1), and the corresponding dppm derivative, [(dppm)(AuSePh)2] (3), are prepared from Me3SiSePh and the appropriate (phosphine)chlorogold(I) complex. The reaction between Ph3PAuCl, Ph2Se2 and AgSbF6 leads to the salt [(Ph3PAu)2SePh]+SbF−6 (2), with a bridging PhSe ligand. X‐ray structure analyses of 1 and 2 confirm the expected linear geometry at gold and reveal short Au‐Au contacts; both compounds may thus be regarded as loose dimers.
Aza‐Enamine, VIII. Elektrophile Substitutionsreaktionen am Azomethin‐C‐Atom von Aldehyddialkylhydrazonen: Vilsmeier‐Formylierung und Folgereaktionen
Authors: Brehme Rainer
Published: July 2007

Aza‐enamines, VIII. — Electrophilic Substitution Reactions at the Azomethine C‐Atom of Aldehyde Dialkylhydrazones: Vilsmeier Formylation and Consecutive Reactions

The reaction of hydrazones 1 with the Vilsmeier reagent yields 3‐phenyl‐1,4,5‐triaza‐1,3‐pentadienium salts according to their aza‐enamine character. Hydrolysis of 2 gives 1‐phenylglyoxal 1‐dialkylhydrazones 3, which rearrange in acidic media to 1‐phenylglyoxal 2‐dialkylhydrazones 4. Compound 3h forms the dihydropyrroloimidazole 5 in boiling ethanol. Pyrrolotriazinium salt 6 is obtained by the reaction of 1b with the isolated Vilsmeier reagent from dimethylformamide/oxalyl chloride.
Organische Synthesen mit Übergangsmetallkomplexen, 47. 1‐Chroma‐1,3‐diene durch Aminoalkenylierung von Methylcarben‐Chromkomplexen mit sekundären Amiden
Authors: Aumann Rudolf , Hinterding Peter
Published: July 2007

Organic Syntheses via Transition Metal Complexes, 47. — 1‐Chroma‐1,3‐dienes by Aminoalkenylation of Methylcarbene Chromium Complexes with Secondary Amides

4‐(NH‐Amino)‐1‐chroma‐1,3‐dienes [= β‐(NH‐Amino)alkenylcarbene chromium complexes] (CO)5CrC(OEt)CHC‐(NHMe)R (Z)‐6 (R  Me, Et, iPr, tBu, Ph) have been obtained with high stereoselectivity in 53–69% yields by the aminoalkenylation of (CO)5CrC(OEt)Me (1a) with secondary amides OC(NHMe)R (5, R  Me, Et, iPr, tBu, Ph) in the presence of POCl3/Et3N.
The laboratory generation of potentially interstellar cumulenes S(Cn)S (n = 2–6) and their radical cations
Authors: Sülzle Detlev , Beye Norbert , Fanghänel Egon , Schwarz Helmut
Published: July 2007

The title compounds are generated and characterized in the gas phase by tandem mass spectrometry (neutralization‐reionization mass spectrometry); it is demonstrated that both even and odd‐numbered polycarbon disulfides S(Cn)S(n = 2–6) are stable species. The elusiveness of the even‐numbered analogues (n = 2, 4, 6) in the condensed phase must be due to facile intermolecular reactions.
Facile catalytic conversion of carboxylic acids into thiocarboxylic S‐acids by the Ph3SbO/P4S10 system
Authors: Nomura RyǒKi , Miyazaki Shin‐Ichiro , Nakano Takahiro , Matsuda Haruo
Published: July 2007

Thiocarboxylic S‐acids 2 are readily prepared by direct sulfuration of the corresponding carboxylic acids 1 catalyzed by Ph3SbO/P4S10 under mild conditions.
Intramolecularly stabilized organoaluminium, ‐gallium and ‐indium derivatives crystal structures of {o‐[(dimethylamino)methyl]phenyl}dimethylgallium and {o‐[(diethylamino)methyl]phenyl}dimethylindium
Authors: Schumann Herbert , Hartmann Uwe , Wassermann Wilfried , Dietrich Andreas , Görlitz Frank H. , Pohl Ludwig , Hostalek Martin
Published: July 2007

Intramolecularly stabilized four‐coordinated organoaluminium, ‐gallium, and‐indium compounds R2MC6H4CH2NR'2‐(2) (1–7), Me2MCH2C6H4NMe2‐(2) (8, 9), Me2MCH2C6H4CH2‐NMe2‐(2) (10, 11), and Me2GaC6H4NMe2 (12) have been synthesized from O ‐[(dialkylamino)methyl]phenyllithium, [O ‐(dimethylamino)phenyl]methyllithium, {O ‐[(dimethylamino)methyl]phenyl}methyllithium and O ‐(dimethylamino)phenyllithium, respectively. The 1H‐, 13CNMR, and mass spectra of the new compounds and the X‐ray crystal structures of 2 and 7 are reported and discussed.
Synthesis of allenes by 1,6‐addition of organocuprates to polarized enynes
Authors: Krause Norbert
Published: July 2007

Ten β‐allenic esters, ketones, and thioesters 15 bearing alkyl, alkenyl, aryl, and trimethylsilyl groups are synthesized in 57‐ 85% yield by 1,6‐addition of organocuprates to polarized enynes 10. The dependence of the regioselectivity of the protonation of the allenyl enolate intermediate 7 on the protonating agent is studied: pure allenes are obtained by quenching the intermediate with pivalic acid at −80°C. The method is applied in a short synthesis of pseudoionone (18).
Synthese von Imidazolidin‐Derivaten aus Dicyanessigsäureestern
Authors: Neidlein Richard , Sui Zhihua
Published: July 2007

Synthesis of Imidazolidine Derivatives from Dicyanoacetates

By nucleophilic additions of amino acids to one cyano group of salts of alkyl dicyanoacetates 1 followed by ring‐cyclisation reactions the 4‐imidazolidinone derivatives 3, 5 are obtained.
Phenylazo‐substituierte Triphenylmethylium‐Systeme
Authors: Hellwinkel Dieter , Fritsch Helmut
Published: July 2007

Phenylazo‐Substituted Triphenylmethylium Systems

Triphenylmethanols (or their ethers) bearing phenylazo groups react with trifluoroacetic acid to give deeply colored solutions of the tritylium ions 7+ ‐ 9+, (RC6H4N  N‐C6H4)n C(C6H5)3‐n (R  H, Me, C1, NOz, MeO, H2N, Me2N), whose long wavelengths VIS absorptions and lowfield 1H‐ NMR signals are consistent with the existence of through‐ conjugated n‐electron systems. After addition of trifluorometh‐ anesulfonic acid significant hypsochromic shifts of the VIS bands as well as additional proton deshieldings in the 1HNMR spectrum are observed, which are in accordance with the formation of proximally azo‐protonated phenylazotrity‐ lium ions 7+·H+, 8+·2H+, and 9+·3H+, (RC6H4NNH‐ C6H4)nC(C6H53 ‐ n. Fully analogous acid‐strength‐dependent ionisation/protonation reactions result for the overall p‐sub‐ stituted ions 17+, 18+, (RC6H4N NC6H4)C(C6H4R)2 (R, R'  Me, MeO, Me2N), as well as for the azobistritylium system,10 (C6H5)2CC6H4NNC6H4(C6H52, and its azoxy deriv‐ ative 11. The linearly extended bis‐ and trisazo systems 19+, 22+, MeC6H4N  N(C6H4N  N)1,2C6H4C(C6H5)2 and the (ph+e‐ny1azo)styryl system 20+, MeC6 H4N  NC6H4CH  CHC6H4C‐ (C6H5), in trifluoroacetic acid do not show any significant color changes relativ to the corresponding monofunctional parent types. In trifluoromethanesulfonic acid, however, compounds 19+, 22+ exhibit the usual bathochromic shifts of the longest wavelength VIS absorptions accompanying the increasing protonation of the polyazo systems. In the case of the tritylium ions containing azomethine bridges, 24+, only for the methoxy derivative 24b+ indications for the existence of the conjuga‐ tively extended tritylium system (MeOC6H4N  CHC6H,)C‐ (C6H5)2 are found. The amide derivatives 26+ ‐ 29+, on the other hand, present no clues for the existence of through‐con‐ jugated systems of the kind ArC(OH)NC6H4Ckz and ArN  C(OH)C6H4CAr2, respectively.
Reactions with aziridines, 53. — Arene hydrides, 9. intermediate substitution in the formation of a benzylic anion by an aromatic radical anion as observed with 1‐benzoyl‐2‐phenylaziridine
Authors: Stamm Helmut , Falkenstein Reinhart
Published: July 2007

The reaction of the title compound 1 with anthracene hydride AH‐ or anthracenide A‐' leads to the formation of the ben‐ zylic anion 9 by fragmentation of the first generated substi‐ tution intermediate 7 or 8. In the reactions with AH‐ the carb‐ anion 9 is completely trapped by protonation with dihydroan‐ thracene AH2 yielding the reduction product 3 (N‐benzoyl‐phenethylamine).phenethylamine). In reactions with A‐' as well as with naph‐ thalenide N‐' the carbanion 9 either abstracts a proton from the solvent THF (yielding 3) or adds to the benzoyl group of unreacted 1 which finally results in P‐benzamido‐ct‐phenyl‐ propiophenone (6).
Acetylierung von N‐(Trimethylsilyl)keteniminen: N‐Acylketenimine und α‐Cyanketone
Authors: Meier Stefan , Würthwein Ernst‐Ulrich
Published: July 2007

Acylation of N‐(Trimethylsfly1)ketenimines: N‐Acylketenimines and α‐Cyano Ketones

The acylation reactions of N‐(trimethylsilyl)ketenimines 1 with different acyl halides 4 yields N‐acylketenimines 2 and/or α‐cyano ketones 3, depending on the substitution pattern of compounds 1 and the halogen atom in 4. In some cases, novel adducts of enamide type 5, 6 are isolated. The new N‐acylketenimines 2a, b are stable at room temperature and have been fully characterized; compounds 2c, d, however, were found to dimerize yielding the 1,3,5‐oxadiazines 7. For comparison, the analogous acylation reactions of nitrile anions were also studied. MNDO calculations are used to rationalize the regiochemistry in terms of kinetic and thermodynamic control.
Inversionsbarrieren Ortho,ortho′‐verbrückter Biphenyle
Authors: Müllen Klaus , Heinz Willi , Klärner Frank‐Gerrit , Roth Wolfgang R. , Kindermann Islinde , Adamczak Oliver , Wette Michael , Lex Johann
Published: July 2007

Inversion Barriers of ortho,ortho′‐Bridged Biphenyls

The syntheses and spectroscopic properties of the ortho,ortho′‐bridged biphenyls 2–19 are described. In the case of 5, 15, and 16 the inversion barrier is determined from the temperature dependence of the NMR spectra (lineshape analysis), in the case of 12, 13, and 14 from the temperature of coalescence, and in the case of 2a, 3b, 7, 17, 18, and 19 from the rate of racemization of the optically active compounds. The experimental inversion barriers, including data from the literature, are compared with those calculated using the extended force field (MM2erw). The conformational behavior of the title systems is significantly affected upon transformation into the corresponding dianion salts. The relevant energy terms are discussed.
On the mechanism of diels‐alder reactions of nitroso alkenes: exo/endo selectivity, stereospecificity, E/Z selectivity, and relative reactivity of various olefins
Authors: Reißig Hans‐Ulrich , Hippeli Claudia , Arnold Thomas
Published: July 2007

The mechanism of the hetero Diels‐Alder reaction of nitroso alkenes 2 with silyl enol ethers and other olefins has been investigated. Using the bicyclic nitroso compound 2a a study of the exo/endo selectivity has demonstrated that the exo approach is preferred with the siloxyethene l a as dienophile. On the other hand, the siloxycyclopentene 1 c gives a mixture of cycloadducts 3 c with an excess of endo product (endo: exo = 82: 18). The stereospecificity of the nitroso alkene cycloaddition could be demonstrated with the stereochemically homogeneous silyl enol ethers 1 b and 1 d. Experiments with enol ethers 1 f and 1 g also occur stereospecifically. α‐Nitrosostyrene 2b reveals surprisingly high kE/Z values when E/Z‐isomeric olefins are compared in competition experiments. Also, a detailed reactivity scale of 2b including various structurally different silyl enol ethers and other typical dienophiles shows that a complex interplay of electronic and steric effects is operating. The large influence of steric effects is taken as evidence for a highly ordered transition state in the cycloaddition. All mechanistic details for the Diels‐Alder reactions of nitroso alkenes 2 with (silyl) enol ethers are in strong accord with a concerted mechanism and exclude the involvement of zwitterions or diradicals as intermediates.
(E,R,R)‐5‐Alkyliden‐2‐tert‐butyl‐6‐methyl‐1,3‐dioxan‐4‐one: Herstellung aus (R)‐3‐Hydroxybuttersäure, Cuprat‐Additionen und Hydrolysen zu 3‐Hydroxycarbonsäuren mit chiralen sekundären Alkylgruppen in 2‐Stellung
Authors: Amberg Willi , Seebach Dieter
Published: July 2007

(E,R,R)‐5‐Alkylidene‐2‐tert‐butyl‐6‐methyl‐1,3‐dioxan‐4‐ones: Preparation from (R)‐3‐Hydroxybutyric Acid, Cuprate Additions, and Hydrolyses to 3‐Hydroxycarboxylic Acids with Chiral Secondary Alkyl Substituents in the 2‐Position

Li enolates of (R,R)‐2‐tert‐Butyl‐6‐methyl‐1,3‐dioxan‐4‐one add to aliphatic or aromatic aldehydes with relative topicity Re,Re (2: 1 to 10: 1, 9 examples). The title compounds are obtained from these aldol adducts by dehydration through mesylates (5 examples, total yields from the dioxanone 35–55%). Cuprate additions (R2CuLi/F3BOEt2) to these alkylidene dioxanones and quenching with acid produce 5,6‐trans‐substituted dioxanones in an overall anti addition of R and H to the exocyclic double bond from the Re and the Si face, respectively (5: 1 to 40:1, 13 examples, 50–80%). The configurations of the products were assigned by NMR spectroscopy and by chemical correlation. In 8 cases, the dioxanone products were hydrolysed to the corresponding free β‐hydroxycarboxylic acids. It is also demonstrated that transacetalisation of the aldol adducts leads to 1,3‐dioxane‐5‐carboxylic acids (acetal‐protected derivatives of “double aldols”, formally derived from acetic acid, 4 examples). Reduction of these acids with LAH, in turn, produces tris(hydroxyalkyl)methanes (acetal‐protected, 3 examples). All chiral products described herein are enantiomerically pure.
Synthese und Struktur von Bis[bis(diisopropylamino)phosphino]chalkogeniden
Authors: Westerman Hermann , Nieger Martin , Niecke Edgar
Published: July 2007

Synthesis and Structure of Bis[bis(diisopropylamino)phosphino]chalcogenides

Phosphorodiamidous chalcogeno‐anhydrides [(R2N)2P]2X (R = Me2CH; X = S, Se, Te) (2a‐c) have been obtained by insertion of elemental sulfur, selenium, or tellurium into the P–P bond of the corresponding diphosphane (1). The structure of 2a and 2c has been confirmed by an X‐ray diffraction.
Derivate des Borols, XVI Bis(borol)nickel‐Komplexe2)
Authors: Herberich Gerhard E. , Englert Ulli , Hostalek Martin , Laven Ralf
Published: July 2007

Derivatives of Borole, XVI1),—Bis(borole)nickel Complexes2)

The dilithium 1‐(dialkylamino)dihydroborolediides Li2[C4H4‐BNR2] 2a, b: R = Me, Et) react with NiCl2 · DME to give bis(borole)nickel complexes Ni(C4H4BNR2)2. Nucleophilic substitution reactions are used to produce a large variety of derivatives Ni(C4H4BR)2 1 (e.g. R = H, tBu, F, Cl, Br, I, OH, OMe). Treatment of Ni(C4H4BCl)2 (tg) with LiO(CH2)3OLi in THF produces a polymer and a dinuclear complex (μ‐{η5:η5‐[(CH2)3(OBC4H4)2]}2Ni2 (3) which crystallizes from CH2Cl2 as solvate 3 · CH2Cl2. The complexes 1g and 3 · CH2Cl2 are characterized by X‐ray diffraction work. Barriers to internal ring‐ring rotation are measured by variable‐temperature NMR spectroscopy. The B—H bond of Ni(C4H4BH)2 (1a) is remarkably inert and does not react with H2O or with carboxylic acids in THF at room temperature. With PhCHO slow formation of the benzyloxy compound Ni(C4H4BOCH2Ph)2 (1 m) is observed at 100°C. For typical complexes such as the phenyl derivative 1e cyclic voltammetry in CH2Cl2 reveals an irreversible oxidation at 1.32 and a quasi‐reversible reduction at –1.37 V vs. SCE.
Darstellung von (Perfluoralkyl)halogeno‐1,3‐diselenetanen aus entsprechenden Selenocarbonylfluoriden und Umsetzungen mit Bortrichlorid sowie Arsenpentafluorid1)
Authors: Haas Alois , Spehr Michael , Boese Roland
Published: July 2007

Preparation of (Perfluoroalkyl)halogeno‐1,3‐diselenetanes from the Corresponding Selenocarbonyl Fluorides and Reactions with Boron Trichloride or Arsenic Pentafluoride1)

Reactions of Hg(SeRt)2 (Rt = C2F5, C3F7, CF3) with (C2H5)2 All or All3 in octamethylcyclotetrasiloxane produce the unstable perfluoroalkaneselenocarbonyl fluorides 1 [R1 = CF3 (1 a), C2F5 (1 b), CF3Se (1 c)]. These compounds are very reactive and polymerize to rubberlike products. On heating the polymers decompose almost quantitatively to the monomers or dimers. In CFCl3 solution 1 dimerizes at 20°C in sunlight to the corresponding cis/trans‐1,3‐diselenetanes 2. The structure of 2 b is determined by single crystal X‐ray diffraction. Different selenocarbonyl derivatives add to unsymmetrically substituted 1,3‐diselenetanes 3. 1 a and 1 b react with cyclopentadiene to form the [4 + 2] cycloaddition products 4a and 4c. Halogen exchange reactions take place between 2a — d and BCl3. The cis‐isomers react much faster than the trans‐isomers to give a mixture of cis‐, trans‐forms of 5. When 2c,d is treated with BCl3 it is possible to isolate and characterize the pure trans‐isomer 2d, which is separated by preparative gas chromatography from 5c,d. Fluorine abstraction with formation of 1,3‐diselenetan‐2‐ylium ions (6a — f) are accomplished by reactions of 2 or 3 with AsF5 in SO2.
Zur Kenntnis des “Silanphosphimins” (Phosphasilaethens) tBu2SiPSitBu31,2)
Authors: Wiberg Nils , Schuster Harad
Published: July 2007

On the Knowledge of the “Silanephosphimine” (Phosphasilaethene) tBu2Si = PSitBu31,2)

The lithium phosphide 3 acts as a source for the “silanephosphimine” 2. Thermolysis of 3 at 80–120°C in the presence of Li⊕ (tBu3Si⊖PH), CH2 = CMe2, or CH2 = CHCH = CH2 leads to products 4, 7 or 8, whose formation is interpretable by the reaction of the reactants with intermediately formed 2.
Übergangsmetall‐substituierte Diphosphene, XX1) Synthese und Eigenschaften des Tetrahedrans [(η5‐C5Me5)(CO)2FeP–PtBu]Fe2(CO)6 und der metallierten 1,3‐Diphospha‐2‐propanone [(η5‐C5Me5)(CO)2Fe–PC(O)–PR]Fe2(CO)6 [R = tBu, 2,4,6‐(CF3)3C6H2]
Authors: Weber Lothar , Schumann Hans
Published: July 2007

Transition‐Metal‐Substituted Diphosphenes, XX1). – Synthesis and Properties of the Tetrahedrane [(η5‐C5Me5)(CO)2‐FeP–PtBu]Fe2(CO)6 and the Metalated 1,3‐Diphospha‐2‐propanones [(η5‐C5Me5)(CO)2Fe–PC(O)–PR]Fe2(CO)6 [R = tBu, 2,4,6‐(CF3)3C6H2]

The reaction of [η5‐C5Me5)(CO)2FeP(SiMe3)2 (1) with tBuPCl2 (2a) affords the metalated cyclotetraphosphane [(η5‐C5Me5)‐(CO)2FeP–PtBu]2 (4a) besides the metal‐substituted cyclotriphosphane (η5‐C5Me5(CO)2Fe–P[PtBu]2 (5a) and the diphosphane (η5‐C5Me5)(CO)2FeP(SiMe3)P(Cl)tBu (3a), which are detected in the reaction mixture by 31P‐NMR spectroscopy. Treatment of 4a with excess of Fe2(CO)9 leads to the tetrahedrane [(η5‐C5Me5)(CO)2FeP–PtBu]Fe2(CO)6 (6a) and the 1,3‐diphospha‐2‐propanone derivative [(η5‐C5Me5)(CO)2FePC(O)‐P–tBu]Fe2(CO)6 (7a). Similarily, an analogous complex 7c is obtained from the reaction of in situ prepared (η5‐C5Me5)‐(CO)2FePP–C6H2(CF3)3‐(2,4,6) with an excess of Fe2(CO)9.
On the Electronic Structure of Phosphabutatriene and Related Phosphacumulenes. A Theoretical Study
Authors: Schoeller Wolfgang W. , Welz Udo , Haug Wilfried , Busch Thilo
Published: July 2007

The title compound phosphabutatriene possesses two energetically closely spaced frontier orbitals, as in methylenephosphane and in phosphaallene. They are built up from the π system or the s̀ orbital of phosphorus by interaction with neighboring π bonds. The extension of these frontier orbitals over all (heavy) atoms makes self‐dimerization to different cyclobutane derivatives feasible. Substituent effects on the ordering of s̀ and π are analyzed. Vibrational analyses indicate PC vibrations of low intensity which decrease with increasing length of the heterocumulene chain. The analysis is extended to the two next higher homologs, which are hitherto experimentally unknown.
Untersuchungen zum Reaktionsverhalten von Benzocyclopropen unter Yb(fod)3‐Katalyse
Authors: Neidlein Richard , Krämer Bettina
Published: July 2007

Experiments Concerning the Reactions of Benzocyclopropene under Yb(fod)3 Catalysis

1,3‐Dihydroisobenzofuran derivatives 3a – e and 5a – c are obtained by reactions of α,β‐unsaturated carbonyl compounds with benzocyclopropene (1). The yields increase by addition of Yb(fod)3. Aromatic aldehydes react in the same way. Yb(fod)3 has no influence on the reactions of α,β‐unsaturated hydrazones with 1.
Synthese heterocyclischer Dialkine und deren Umsetzung mit CpCo(CO)2
Authors: Gleiter Rolf , Rittinger Stefan , Langer Heinrich
Published: July 2007

Synthesis of Heterocyclic Diynes and their Reaction with CpCo(CO)2

The preparation of the heterocyclic diynes 1,6‐dithia‐3,8‐cyclodecadiyne (1b), thia‐3,8‐cyclodecadiyne (11), 1‐thia‐6‐selana‐3,8‐cyclodecadiyne (12), oxa‐3,8‐cyclodecadiyne (13), 1,6‐dioxa‐3,8‐cyclodecadiyne (14), 1‐oxa‐6‐thia‐3,8‐cyclodecadiyne (15), 1,6‐diselena‐3,8‐cyclodecadiyne (26), thia‐3,9‐cyclounde‐cadiyne (22a), thia‐3,13‐cyclopentadecadiyne (22b) and its selena analogues 23a, 23b is described. The thia and monoselena compounds are obtained by a thia‐ or selenacyclization of the corresponding dibromides. Compound 26 has been obtained by a Misumi coupling reaction. The thiacycloalkadiynes of medium‐sized rings (10, 11) react with CpCo(CO)2 to yield [2,2](2,5)thiophenophane derivatives. Acyclic thiadialkynes or thiacycloalkadiynes of larger ring size (22b) with CpCo(CO)2 by [2 + 2 + 2] cycloaddition.
Ten‐Membered Heterocyclic Diynes X‐ray Structure Analysis and PE‐Spectroscopic Investigations
Authors: Gleiter Rolf , Rittinger Stefan , Irngartinger Hermann
Published: July 2007

X‐ray investigations on the ten‐membered heterocyclodiynes 1 – 4 reveal a chair‐like conformation for all four compounds. The triple bonds are oriented parallel to each other, the distances between them varying between 3.10 Å (2) and 2.91 Å (1). All triple bonds are slightly bent, the deviation from 180° varies between 6 – 10°. The photoelectron spectra of 1 and 3 – 6 have been recorded. The first six bands have been assigned by comparing them with related species and MO calculations. In the case of 3 – 6, the HOMO is predicted to be a long pair combination. The splitting between the in‐plane π‐linear combinations η−i, η+i ranges from 0.9 eV (5) up to 1.5 eV (4).
Reactions of Benzocycloheptenes with Dienophiles
Authors: Adam Waldemar , Balci Metin , Ceylan Zeynep , Hinz Ricardo Francisco
Published: July 2007

The Diels‐Alder reactions of 5H‐benzocycloheptene (1) with tetracyanoethylene (TCNE) afforded the [2+2] and [4+2] cycloadducts 7, 8, and 10 and the benzodicyanoheptafulvalene 9. The norcaradiene product 10 was synthesized independently by cycloaddition of TCNE to 7H‐benzocycloheptene (3). The addition of 4‐methyl‐1,2,4‐triazoline‐3,5‐dione (MTAD) to 3 gave bis‐urazole 13, which was formed by ene reaction followed by [4+2] cycloaddition. The spirocycloheptatriene 15 gave with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione (PTAD) the bisurazole 16.
Abfangen von Hexafluorselenoaceton durch Cycloadditionen mit Dienen sowie Darstellung von Hg[SeCF(CF3)2]2 und (CH3)3SiSeCF(CF3)2
Authors: Haas Alois , Limberg Christian , Spehr Michael
Published: July 2007

Scavenging of Hexafluoroselenoacetone by Cycloadditions with Dienes and Preparation of Hg[SeCF(CF3)2]2 and (CH3)3SiSeCF(CF3)2

Bis(perfluoroisopropylseleno)mercury (2) was obtained from 2,2,4,4‐tetrakis(trifluoromethyl)‐1,3‐diselenetane (1) and HgF2 in DMF, and (perfluoroisopropylseleno)trimethylsilane (3) from 2 and (CH3)3Sil. The reaction of 2 with (C2H5)2All as well as the pyrolysis of 1 yield a deep purple liquid in very small amounts, not sufficient for further characterisation, which is assumed to be hexafluoroselenoacetone (4). However, 4 is formed as an intermediate in the reaction of hexafluoropropene with CsF and selenium and can be trapped by isoprene or anthracene to form 5a, 5b, and 6, respectively. In boiling benzene a transformation of (CF3)2CSe from 6 to 2,3‐dimethyl‐1,3‐butadiene is accomplished yielding 7 in a retro Diels‐Alder cleavage.
Röntgenstrukturuntersuchung von α‐(Trimethylsilyl)benzyllithium·Tetramethylendiamin [C6H5CH(SiMe3)Li·TMEDA] und α‐(Phenylthio)‐benzyllithium·3 Tetrahydrofuran [C6H5CH(SPh)Li·(THF)3] – zwei zentral‐chirale Benzyllithium‐Verbindungen
Authors: Zarges Wolfgang , Marsch Michael , Harms Klaus , Frenking Gernot , Boche Gernot , Koch Wolfram
Published: July 2007

Crystal Structure of α‐(Trimethylsilyl)benzyllithium·Tetramethylethylendiamin [C6H5CH(SiMe3)Li·TMEDA] und α‐(Phenylthio)‐benzyllithium·3 Tetrahydrofuran [C6H5CH(SPh)Li – (THF)3] – Two Benzyllithium Compounds with Central Chirality

The crystal structure analyses of [C6H5CH(SiMe3)Li·TMEDA] (6) and of [C6H5CH(SPh)Li·(THF)3] (7, in which the positions of the benzylic hydrogen atoms have been determined experimentally, reveal compounds with pyramidal benzylic carbon atoms. In 6 lithium is λ2‐bound to Cipso and α of the substituted benzylic anion which leads, together with the TMEDA molecule, to a tetra‐coordinated lithium atom. In 7 only one Li – C bond is formed, namely that to Cα. Additional coordination with three THF molecules results also in a tetracoordinated lithium atom, The extent of the pyramidalization in 6 and 7 is qualitatively in agreement with quantum‐mechanical ab initio calculations [G86, MP2/6‐311+ + G(d,p)].
Inter‐ and Intramolecular Hetero Diels‐Alder Reactions, 31. Synthesis of D‐Homoestrone Derivatives by Tandem Knoevenagel Hetero Diels‐Alder Reactions from Natural Estrone
Authors: Tietze Lutz F. , Wölfling János , Schneider Gyula
Published: July 2007

The tandem Knoevenagel hetero Diels‐Alder reaction of the secoestrone derivative 8 with dimethylbarbituric acid (9a). Meldrum's acid (9b), and the pyrazolones 13a–c stereoselectively affords the D‐homoestrone derivatives 11a, 12, and 14a–c, respectively, with the 16α,17aα configuration in excellent yield. In the reaction of 8 with 9a, b only one diastereomer can be detected, whereas in the reaction of 8 with 13a–c a small amount of the isomeric adducts 15a–c has also been found.
Übergangsmetall‐Stannyl‐Komplexe, 31) Metall, Wasserstoff, Zinn‐Dreizentrenbindung bei Hydrido‐Stannyl‐Komplexen der 6. Nebengruppe
Authors: Piana Hermann , Kirchg äßner Uwe , Schubert Ulrich
Published: July 2007

Transition‐Metal Stannyl Complexes, 3. – Metal, Hydrogen, Tin Three‐Center Bonding in Group VI Hydrido Stannyl Complexes

The hydrido stannyl complex (π‐1,3,5‐Me3C6H3)(CO)2Cr(H)‐SnPh3 (1) is prepared by photochemical reaction of (π‐1,3,5‐Me3C6H3)(CO)3Cr with HSnPh3. The 119SnHCr coupling constant (327.6 Hz) and an X‐ray structure analysis [Sn – H 202(4), Cr – H 159(4), Cr – Sn 270.16(6) pm] show that the Sn – H bond is coordinated in an η2 fashion. The complexes (CO)4(R3P)‐W(H)SnPh3 (R3PPh3P, MePh2P) (2) and (CO)3(dppe)M(H)‐SnR3 (MCr, SnR3=SnPh3; MMo, SnR3=SnMe3, SnPh3; MW, SnR3=SnMe3, SnPh2Me, SnPh3) (4 – 6) are obtained either by thermal reaction of (CO)4(R3P)W(THF) or (CO)3(dppe)ML (LTHF, acetone) with HSiR3, or by photochemical reaction of (CO)4(dppe)M with HSnPh3. Reaction of (CO)4(Ph3P)W(THF) with HSnMe3 yields (CO)4(Ph3P)W(Sn‐Me3)2 (3). The Sn,M,H coupling constants in the complexes 2 and (CO)3(dppe)M(H)SnR3 (MCr, Mo) are in the range of 250 – 315 Hz and therefore these complexes seem to contain an η2‐coordinated stannane. Contrary to this, the SnWH coupling constants in (CO)3(dppe)W(H)SnR3 are considerably lower (70 – 90 Hz), suggesting complete oxidative addition of the H – Sn bond. The complexes (CO)3(dppe)M(H)SnPh3 decompose in benzene solution at room temperature to give, inter alia, hexaphenyldistannane. Ph6Sn2 · 2 C6H6 crystallizes in the space group \documentclass{article}\pagestyle{empty}\begin{document}$ R\bar 3 $\end{document} (Z=1); in the crystal lattice the benzene molecules are perpendicular to the three‐fold axis of symmetry of the distannane molecule.
Chromophore Systeme, 2. Konformation und Lichtabsorption von (2‐Alkoxyvinyl)ethandionen
Authors: Effenberger Franz X. , Kramme Roland , Lindner Hans Jörg , Martin Georg , Martin Hans‐Dieter , Mayer Bernhard
Published: July 2007

Chromophoric Systems, 2. – Conformation and Absorption of Light in (2‐Alkoxyvinyl)ethanediones

The unusual color properties of yellow 1,2‐bis(4,5‐dihydrofuran‐3‐yl)ethane‐1,2‐dione (1) and colorless 1,2‐bis(5,6‐dihydro‐4H‐pyran‐3‐yl)ethane‐1,2‐dione (2) in the solid state and in solution are investigated by crystal structure analysis, UV‐Vis, PE, and 13C‐NMR spectroscopy as well as by reparameterized force‐field calculations. Dione 1 takes an antiperiplaner CO/CO conformation of its chromophore in the solid state whereas dione 2 is twisted in this respect by 102°. In solution both chromophores are not planar, but 1 is less distorted (ca. 142°) than dione 2 (ca. 126°). The calculated rotational barrier for CO/CO twisting amounts to 0.9 kcal mol−1 for 1 and to 2.2 kcal mol−1 for 2.
Synthese eines chiralen, nicht‐racemischen Aziridinons (α‐Lactams)1,2)
Authors: Quast Helmut , Leybach Holger
Published: July 2007

Synthesis of a Chiral, Nonracemic Aziridinone (α‐Lactam)1,2)

(S)‐tert‐Leucine [(S)‐14] is diazotized affording a mixture of the expected α‐chloro and α‐hydroxy acids (S)‐15 and (S)‐16 and the rearranged β‐chloro and β‐hydroxy acids (R)‐12 and (S)‐11. Separation produces a 51% yield of pure (S)‐15 (e.e. ° 97.4%) which is converted via the acid chloride (S)‐17 into the α‐chloro amides (S)‐18a and b (e.e.=99.0 and 95.2%, respectively). On treatment with tBuOK, the latter is converted into the α‐lactam (R)‐22b (59%, e.e. ° 91.0%, [α°=−293.7), which is accompanied by small amounts of its ring‐opening product (R)‐23b. Only the α‐amino ester (R)‐23 a is formed from the α‐chloro amide (S)‐18a and tBuOK. While the enantiomers of the halo amides 13, 18a, b, 24a, b and of the 3‐pentyl esters of the hydroxy acid 16 are separated by GC on chiral columns, the α‐lactam 22b and the α‐amino esters 23a, b require conversion into separable derivatives without involving the stereogenic center. Thus, alkaline hydrolysis of 22b as well as acidic cleavage of 23 yield the α‐amino acids 25 which are cyclized to the oxazolidine‐2,5‐diones 26 by means of bis(trichloromethyl) carbonate (“triphosgene”). As shown by the high enantiomeric excess of the products derived from (S)‐tert‐leucine [(S)‐14] none of the reactions described results in a considerable degree of racemization. Authentic samples of 11 and 12 are synthesized from the Reformatzky product 21. The absolute configurations of the major enantiomers derived from (S)‐14 are based on the retention on chiral GC columns, the signs of optical rotations, and CD spectra. The mechanism of the rearrangement leading to the β‐hydroxy and β‐chloro acids (S)‐11 and (R)‐12 is interpreted in terms of a stereospecific 1,2‐methyl shift occurring simultaneously with the ring cleavage of the (protonated) α‐lactone (R)‐2 (R=tBu) which is the crucial intermediate formed in the diazotization of (S)‐14.
Polylithiumorganic Compounds, XIIII. “Phospha[3]radialenes” — Reactive Intermediates in the Synthesis of “Phospha[6]radialenes”
Authors: Maercker Adalbert , Brieden Walter
Published: July 2007

The reaction of the dilithiobutadiene 1 with various dichloroorganylphosphanes in diethyl ether at ‐80°C leads to the formation of the novel phosphiranes 5a–e and 6a, 6c–e in up to 86% yield. A thermal isomerization of the alkenylidenephosphiranes 6 leads to the complete formation of the corresponding “phospha[3]radialenes” 5. Quaternization of the latter gives the cyclic phosphonium salts 8b–d, on addition of iodomethane, while methylation of 5a leads to the acyclic 9a. The phosphiranes 5c–e and 6c–e are converted into the bis‐ (alkylchlorophosphino)butadienes 10c–e by addition of the corresponding dichloroorganylphosphane at room temperature, whereas 5a,b and 6a are quite unreactive. The interaction of 10e with 1 gives the “phospha[6]radialene” 12e, a formal dimer of 5e. The isolated 1,4‐diphosphorinane 12e exists in a rigid trans‐chair conformation as revealed by its NMR spectra.
Gas‐Phase Kinetics of the Thermal 1‐Alkoxy‐1‐vinylcyclopropane to 1‐Alkoxy‐1‐cyclopentene Rearrangement
Authors: McGaffin Gregory , Meijere Armin De , Walsh Robin
Published: July 2007

The title studies have been carried out with both 1‐vinyl‐1‐cyclopropyl methyl ether (1‐OMe) and 1‐vinyl‐1‐cyclopropyl ethyl ether (1‐OEt) in the temperature ranges 274.6–324.5 and 273.6 – 323.0°C, respectively. Both reactions predominantly give the vinylcyclopropane‐cyclopentene (VCP‐CP) rearrangement products 1‐cyclopenten‐1‐yl methyl ether (2‐OMe) and 1‐cyclopenten‐1‐yl ethyl ether (2‐OEt). Additionally, 2‐OEt eliminates ethene (3) in a consecutive reaction at a lower reaction rate compared with the VCP‐CP rearrangement. The rearrangements obey first‐order kinetics and have been shown to be homogeneous, pressure‐independent reactions with the following Arrhenius equations:

The Arrhenius parameters represent reliable values for general 1‐vinyl‐1‐cyclopropyl alkyl ether→1‐cyclopenten‐1‐yl‐alkyl ether (1‐OR→2‐OR) rearrangements within a large temperature interval in the gas phase. The results support a mechanism proceeding via a diradical. The stabilizing effect of methoxy substitution is discussed.