bluuebunny/crossref_metadata_2025_split huggingface dataset:
Routes to Stannoles, Stannolenes and 1‐Stanna‐4‐bora‐2,5‐cyclohexadienes – Crystal Structure of a Triorganotin Cation Stabilized by π1‐Coordination
Authors: Wrackmeyer Bernd , Kundler Sabine , Boese Roland 
Published: July 2007

AbstractDi‐1‐alkynyltin compounds (1) react with triorganoboranes R3B [2a (REt), 2b (RiPr)] to give (η21‐alkynyl)tin compounds 3 (REt) and 4 (RiPr) in which a cationic three‐coordinate tin centre is stabilized by intramolecular side‐on coordination to the CC bond of an alkynylborate fragment. An X‐ray analysis of 3e, prepared from Me2Sn(CCiPr)2 (1e) and Et3B, proves the coordination of the tin atom to the CC bond as well as a weak BC bond. An important dynamic process, i.e. exchange of the alkynyl group between boron and tin, is shown by 11B and 119Sn NMR at variable temperature. Most of the intermediates 3 react with an excess of Et3B by a second intramolecular 1,1‐ethyloboration to dialkenyltin derivatives 7 which readily rearrange to the 3‐stannolenes 8. Without an excess of Et3B, intramolecular 1,1‐vinyloboration (leading to the stannoles 5) competes with intramolecular 1,1‐ethyloboration (leading to 1‐stanna‐4‐bora‐2,5‐cyclohexadienes 9). The latter route is preferred in the case of most of the intermediates 4 (intramolecular 1,1‐isopropyloboration) and affords the six‐membered rings 10 (RiPr). 11B‐and 13C‐NMR data indicate that the heterocycles 9 (REt) adopt a flatter conformation than 10 (RiPr).
(Di‐tert1‐butylfluorsilyl)hydrazin, ein Baustein für strukturisomere N,N‐ und N,N′1‐Bis(silyl)hydrazine
Authors: Drost Christian , Klingebiel Uwe 
Published: July 2007

(Di‐tert1‐butylfluorosilyl)hydrazine, a Building Block for Structure‐Isomeric N,N‐ and N,N′1‐Bis(silyl)hydrazinesDi‐tert1‐butyldifluorosilane reacts with monolithiated hydrazine to give the stable monosilylated hydrazine 1 and the six‐membered ring 2. The bis(fluorosilyl)hydrazine 3 is formed in a condensation reaction by heating 1 at 220°C. HCl elimination between 1 and chlorosilanes leads to the N,N′1‐disubstituted hydrazines 4 and 5. An N,N′1‐bis(silyl)hydrazine 6 is obtained in the reaction of lithiated 1 with difluorodiisopropylsilane while an N,N1‐bis(silyl)hydrazine 7 is formed with tert1‐butyltrifluorosilane. Structural isomerism (8–11) is observed in reactions of lithiated 1 with [(trifluorosilyl)amino]silanes.
Tri‐, Tetramethylbullvalene und Hexamethylbibullvalenyl
Authors: Rebsamen Karl , Schröder Gerhard 
Published: July 2007

Tri‐, Tetramethylbullvalenes and HexamethylbibullvalenylThe known monomethylbullvalenes 6 and dimethylbullvalenes 7 are supplemented by tri‐8 and tetramethylbullvalenes 9 as well as the hexamethylbibullvalenyl 10. The isomer distributions of the methylbullvalenes 6–9 are determined by NMR‐spectroscopy. A vicinal arrangement of two methyl groups is not found. The 4‐, 6‐, 10‐positions are slightly preferred in respect to the 3‐, 7‐, 9‐positions. In the case of the methylbullvalenes 8 and 9 methyl groups occupy additionally the 1‐, 2‐, 8‐ but not the 5‐position. Contrary to tetrabromobullvalenes 5, isomers of 9 show no pronounced kinetic stability.
(R)1‐(+)1‐Pantolactone Acrylate as a Chiral Auxiliary in the Baylis‐Hillman Reaction
Authors: Khan Abdullah A. , Emslie Neville D. , Drewes Siegfried E. , Field John S. , Ramesar Niyum 
Published: July 2007

Abstract2,6‐Dialkyl‐5‐methylene‐1,3‐dioxan‐4‐ones were prepared in good diastereomeric excess by treating pantolactone acrylate with a series of selected aldehydes in the Baylis‐Hillman reaction. With benzaldehyde and trichloroacetaldehyde, non‐cyclic products resulted. In the case of the latter aldehyde the α1‐hydroxyalkyl acrylate 5b was isolated as a single diastereomer and its absolute configuration established by X‐ray crystallography.
Stereoselective Synthesis of α,β‐trans1‐Spiro‐β1‐lactones by Diels‐Alder Cycloaddition of 1,3‐Dienes to α1‐Methylene‐β1‐lactone and Their Decarboxylation by Pyrolysis to (E)1‐Alkylidenecycloalkenes, a Convenient Olefination Method
Authors: Adam Walder , Salgado Victor Oswaldo Nava , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von 
Published: July 2007

AbstractA number of spiro‐β1‐lactones was prepared in good to excellent yields through stereoselective [4 + 2] cycloaddition of β1‐isopropyl‐α1‐methylene‐β1‐lactone (1) with acyclic, cyclic, heterocyclic and aromatic 1,3‐dienes by sealed‐tube reaction at moderate temperatures (50 – 130°C). Flash pyrolysis of the resulting spiro‐β1‐lactones 2 in the gas phase at 400°C afforded by decarboxylation exclusively the corresponding (E)1‐isopropylidenealkenes in high yields with retention of the initial geometry and without double bond isomerization. This olefination method constitutes an excellent stereoselective synthesis of (E)1‐alkylidenecycloalkenes.
1,3‐Bis(2‐thienylmethylene)1‐1H,3H1‐thieno[3,4‐c]thiophene: A Precursor for a New Low Band Gap Polymer
Authors: Hanack Michael , Schmid Ulrich , Röhrig Ursula , Toussaint Jean‐Marc , Adant Christine , Brédas Jean‐Luc 
Published: July 2007

AbstractA new precursor, 1,3‐bis(2‐thienylmethylene)1‐1H,3H1‐thieno‐[3,4‐c]thiophene(9), for polyarenemethylenes (PAM), which are predicted to be low band gap polymers, is obtained by a Knoevenagel‐type condensation of 1H,3H1‐thieno[3,4‐c]thiophene 2‐oxide (7) with 2‐thiophenecarbaldehyde followed by reduction of the intermediate sulfoxide 8 with 2‐chloro‐1,3,2‐benzodioxaphosphole. Several investigations with cyclic voltammetry and UV‐Vis‐NIR spectroelectrochemistry (SEC) are carried out on 9. The experimental data are compared with the results of electronic band structure calculated on the basis of an MNDO‐optimized geometric structure by VEH pseudopotential method.
Desaminierungsreaktionen, 54. Zerfall von 1‐Cyan‐1‐propandiazonium‐Ionen
Authors: Bunse Michael , Kirmse Wolfgang 
Published: July 2007

Deamination Reaction, 54[1]. – Decomposition of 1‐Cyano‐1‐propanediazonium IonsThe nitrous acid deamination of 2‐aminobutanenitrile (9) was studied with regard to product distribution and stereochemistry. The formation of 2‐(hydroxyimino)butanenitriles (21, 22; 8 – 28%) indicates the intervention of 1‐cyanopropyl radicals (24) that are captured by NO. The polar reactions lead mainly to elimination (10 – 13) and nucleophilic substitution (14 – 16), rearrangement playing a minor role. (R)‐9 was prepared from (R)1‐2‐aminobutanoic acid. The nitrous acid deamination of (R)‐9 afforded the cyanohydrin 16 with 81% net inversion. Owing to destabilization of the carbocation 26 by CN, the SN2 route of nucleophilic displacement is preferred over SN1. The influence of CN is shown to be smaller than that of CF3.
Desaminierungsreaktionen, 55. Zerfall von 2‐Cyannorbornan‐2‐diazonium‐Ionen
Authors: Kirmse Wolfgang , Minkner Dirk , Siegfried Rainer 
Published: July 2007

Deamination Reactions, 55[1]. – Decomposition of 2‐Cyanonorbornane‐2‐diazonium IonsThe epimeric 2‐aminonorbornane‐2‐carbonitriles (8a and 9a) were prepared from norbornane‐2‐one (7). The nitrous acid deamination reactions of 8a and 9a afforded the nitro compounds 15c and 16c in low exo/endo ratios, presumably by way of 2‐cyano‐2‐norbornyl radicals (12). The major ionic process was found to be a Wagner‐Meerwein rearrangement, leading to 1‐cyano‐2‐norbornyl cations (10) and products 14 derived therefrom. Minor amounts (≤10%) of 2‐hydroxynorbornane‐2‐carbonitriles (15a, 16a) provide suggestive, albeit inconclusive evidence for the trapping of 2‐cyano‐2‐norbornyl cations (11). The decomposition of the endo diazonium ions 9c is also associated with norbornyl → norpinyl rearrangement, giving rise to 17 (≤9%). Stereochemical studies with optically active precursors point to intervention of the 7‐bridged norbornyl cation 13 and of the edge‐protonated cyclopropane 25. The formation of both species is clearly promoted by the cyano group.
[4 + 2]‐Cycloadditionen von Halogenthiazylen an 2‐Chlorpentafluor‐1,3‐butadien
Authors: Boese Roland , Haas Alois , Heβ Thomas 
Published: July 2007

[4 + 2] Cycloadditions of Halogeno Thiazyls with 2‐Chloropentafluoro‐1,3‐butadieneReactions of (XSN)n (n=3, 1; X=Cl, F) with 2‐chloropentafluoro‐1,3‐butadiene provide the 1λ4,2‐thiazines 1a and 1b. Fluorination with KF converts 1a in 88% yield to 1b. CH3OH reacts with 1b to form the 1‐methoxy derivative 1c. The structure of 1c was determined by single‐crystal X‐ray diffraction analysis. With water 1a forms the 1,2‐thiazin‐3‐one 1‐oxide 2.
Benzylgalliumverbindungen. Koordination von Benzylliganden in Cs[(PhCH2)2GaF2]
Authors: Neumüller Bernhard , Gahlmann Frank 
Published: July 2007

Benzylgallium Compounds. Coordination of Benzyl Ligands in Cs[(PhCH2)2GaF2]Dissolving (PhCH2)3Ga (1) in THF yields the complex [(PhCH2)3Ga · THF] (2). Reaction of 1 with dry oxygen in toluene at –78°C leads to [(PhCH2)2GaOCH2Ph]2 (3), which is also formed from 1 and PhCH2OH. The salts K[(PhCH2)2GaF2] (5) and Cs[(PhCH2)2GaF2] (6) were obtained from (PhCH2)2GaCl (4) and KF or CsF, respectively, in acetonitrile. Crystal structures were determined for 2, 3, 6 and {[(PhCH2)2GaCl]2 · toluene} (7). Gallane 2 is a chiral monomeric complex in the solid state. The benzyl substituents create a propeller‐shaped molecule with a counterclock‐wise orientation of the ligands. 3 and 7 are crystallizing as centrosymmetrical dimers with Ga2X2 rings (X=O, Cl). 6 consists in infinite chains of {Cs[(PhCH2)2GaF2]}2 units with Cs–F contacts. In addition to the Cs–F interaction, the coordination of each Cs+ ion by two phenyl rings in a η6‐ fashion is observed.
Synthesen und Struktur von Diborylacetylenen
Authors: Schulz Hartmut , Gabbert Gernot , Pritzkow Hans , Siebert Walter 
Published: July 2007

Syntheses and Structure of DiborylacetylenesReactions of bis(trimethylstannyl)acetylene with 2‐chloro‐1,3,2‐benzodioxaborole derivatives or 9‐chloro‐9‐borabicyclo[3.3.1]nonane lead to the corresponding diborylacetylenes 1a, b and 2. Sodium acetylide reacts with R1R2BCl to give R1R2BC1 (3a, b), which are converted to R1R2BC1R1R2 (4a, b) by lithiation and subsequent treatment with more R1R2BCl (R1=iPr2N, R2=iPr2N or tBu). X‐Ray structure analyses are performed for 1a, 4a, and 4b.
A Second Modification of Potassium Fluorenide and the Structure of Potassium 9‐tert‐Butylfluorenide: Effect of Crystallization Conditions and Substituents on Solid‐State Contact Ion Pair Interactions
Authors: Janiak Christoph 
Published: July 2007

AbstractCrystallization of potassium fluorenide or 9‐tert‐butylfluorenide [formed from potassium metal and fluorene or 9‐tert‐butylfluorene in tetramethylethylenediamine (tmeda)] from a mixture of tmeda, tetrahydrofuran (THF) and diethyl ether yields [K(tmeda)2][C13H9] (1) or {[K(THF)2][μ‐C13H8(tBu)][K(tmeda)][μ‐C13H8(tBu)]}∞ (2). Compound 1 is a monomeric solvated ion pair with one η5‐coordinated fluorenyl and two chelating tmeda ligands and crystallizes in the monoclinic space group C2/c. Compound 1 is an example of polymorphism in organo‐potassium compounds, as a polymeric structure of 1 obtained under slightly different crystallization conditions has been reported earlier. Compound 2 forms a polymeric chain with potassium coordinated to two anellated six‐membered rings from two bridging 9‐tert‐butylfluorenyl systems and alternatingly solvated by one chelating tmeda or two THF. The crystal system for 2 is monoclinic, space group P21/c. A comparative AM1 study on the fluorenyl and 9‐tert‐butylfluorenyl anion suggests a steric origin for the haptotropic potassium shift in 2. 1H‐ and 13C‐NMR data for 1 and 2 as well as for 9‐tert‐butylfluorene are reported.
Thioalkylierung der Metall–Kohlenstoff‐Mehrfachbindung in Carbin‐ und Carben‐Komplexen von Molybdän und Wolfram
Authors: Kreißl Fritz R. , Schütt Wolfgang , Stegmair Claudia M. , Ullrich Norbert , Keller Hans , Ostermeier Josef , Herdtweck Eberhardt 
Published: July 2007

Thiomethylation of the Metal–Carbon Multiple Bond of Carbyne and Carbene Complexes of Molybdenum and TungstenCarbyne complexes of molybdenum and tungsten react with dialkyl(methylthio)sulfonium tetrafluoroborate in a stepwise addition of the alkylthio cation to the metal–carbon multiple bond yielding dicationic η3‐dithiomethyl complexes.
Metallorganische Clusterkomplexe mit flächenüberbrückenden Aren‐Liganden, 5[1a]. C–H‐Aktivierung und Bildung eines μ3‐Aren‐Komplexes: Konkurrenzreaktionen beim Aufbau von (CpCo)3‐Clusterkomplexen mit Vinylbenzolen als Liganden
Authors: Wadepohl Hubert , Borchert Till , Büchner Klaus , Pritzkow Hans 
Published: July 2007

Organometallic Clusters with Face‐Capping Arene Ligands, 5[1a].–C–H Activation and Formation of a μ3‐Arene Complex: Competing Reactions During Assembly of (CpCo)3Cluster Complexes with Vinylbenzenes as LigandsA number of ring‐substituted styrenes R(C6H4)C2H3(R=CH3, F) reacts with [CpCo(C2H4)2] (1) to give both the cluster complexes [(CpCo)3{μ3‐η2:η2:η2‐(C6H4R)C2H3}] [2a(R=p‐CH3),2c(R=m‐F),2d(R=p‐F)} with Co3face‐capping arenes and [(μ2‐H)(μ3‐H)(CpCo)3{μ3‐1‐s̀:2‐s̀:η2‐HCC(C6H4R)}] [7a(R=p‐CH3),7b(R=o‐F),7c(R=m‐F),7d(R=p‐F)] with Co3face capping alkynes derived from dehydrogenation of the vinyl group. The X‐ray structure analysis of7aconfirms the 1‐s̀:2‐s̀:η2coordination of the bridging alkyne ligand. In solution the complexes7are fluxional and exhibit migration of the alkyne and hydride ligands on the Co3cluster.
Ring Opening of (η5‐Bicyclo[3.2.0]hepta‐1,3‐dienyl)‐(η4‐tetraphenylcyclobutadiene)cobalt(I) Followed by Cycloaddition
Authors: Butenschön Holger 
Published: July 2007

AbstractThe title reaction, which was detected by a comparison of the DSC analysis of title compound 2 with that of the corresponding bicyclo[3.3.0]octa‐1,3‐dienyl complex 3, takes place at 200°C with various dienophiles (dimethyl fumarate, dimethyl maleate, diphenylethyne, N‐methylmaleinimide). 3,4‐Dimethylenecyclopentenyl complex 12 most likely is the key intermediate of the reaction.
Über (Pentafluorphenyl)thiocarbonyl‐Verbindungen sowie die Synthese und Struktur von (Pentafluorphenyl)phenylsulfin
Authors: Hasserodt Jens , Pritzkow Hans , Sundermeyer Wolfgang 
Published: July 2007

(Pentafluorophenyl)thiocarbonyl Compounds, Synthesis and Structure of Pentafluorophenyl Phenyl SulfineThe C6F5‐substituted thiocarbonyls C6F5–CS–R [R=C6H5 (2), CH3 (4)] are synthesized from the corresponding carbonyl compounds by using in situ formed B2S3. The corresponding highly reactive thioaldehyde (R=H) is trapped with anthracene as Diels‐Alder adduct 7. By oxidation of 2 sulfine 10 is generated which dimerizes in the crystal lattice. An X‐ray crystal structure determination of a trithiaphosphinane 9 was carried out for the first time. The bis‐para‐substituted compound 12 is obtained from perfluorobenzophenone and hydrazine hydrate in a fast reaction.
Konkave Makroheterocyclen
Authors: Mekelburger Hans‐Bernhard , Groβ Jens , Schmitz Jürgen , Nieger Martin , Vögtle Fritz 
Published: July 2007

Concave MacroheterocyclesMacrocyclic compounds of the general type 2 having a spherical shape and a molecular cavity have been synthesized. A „fold and paste”︁‐type cyclization step generates the macroheterocycles 4, 10, 11, 14, and 21. Since this approach is difficult to apply for O‐substituted derivatives, the „spheriphane”︁ 24 was synthesized by intermolecular cyclizaiton. The X‐ray structure analysis of 11 shows intermolecular interactions („dimer formation”︁) in the crystal.
Reaktionen der Borhydride B3H7 und B5H9 mit den ungesättigten Bor‐Stickstoff‐Verbindungen NBtBu2 und NB2tBu3
Authors: Küpper Stefan , Paetzold Peter , Boese Roland 
Published: July 2007

Reactions of the Boron Hydrides B3H7 and B5H9 with the Unsaturated Boron‐Nitrogen Compounds NBtBu2 and NB2tBu3THF · B3H7 reacts with RB≡NR (1, R = tBu) to yield the μ‐amino‐diborane(6) B2H4R(NHR) (5), which crystallizes in the triclinic space group Pī. The reaction of B3H7 with the azadiboriridine NB2tBu3 (2, R = tBu) leads to the known NB2R3 · BH3 (4) and the novel (NB2R3)2B2H4 (6). Product 6 is considered to represent a diaza‐arachno‐octaborane derivative. The iminoborane 1 reacts with B5H9 in the presence of lutidine (L) to give the ionic product [L – BR = NHR][B9H14] (7); our earlier report on the formation of the aza‐arachno‐heptaborate [LH][NB6H8R2] has to be revised. The products from the reaction of B5H9 with NB2R3 are 4 and 6.
Koordinationschemie Perhalogenierter Cyclopentadine und Alkine, XV. Systematischer Aufbau von fünffach ringsilylierten Cyclopentadienyl‐mangan‐Komplexen aus [C5Br5]Mn(CO)3. Molekülstruktur von [C5Br3(SiMe3)2]Mn(CO)3
Authors: Sünkel Karlheinz , Hofmann Julian 
Published: July 2007

Coordination Chemistry of Perhalogenated Cyclopentadienes and Alkynes, XV[1]. – Systematic Generation of Fivefold Ring‐Silylated Cyclopentadienyl Manganese Complexes from [C5Br5]Mn(CO)3. Molecular Structure of [C5Br3(SiMe3)2]Mn(CO)3[C5Br5]Mn(CO)3 reacts in a sequence of alternate bromine‐lithium exchange reactions and electrophilic silylations by SiMe3Cl or SiMe3OSO2CF3 to give [C5Br5‐n(SiMe3)n]Mn(CO)3, where n = 1 (1), 2 (2), or 3 (3). A crystal structure determination of 2 shows the two silyl substituents in the relative 1,3‐orientation. Addition of one or two equivalents of BuLi and SiMe2HCl to a solution of 3 yields [C5Br2‐n(SiMe3)3‐(SiMe2H)n]Mn(CO)3 with n = 1 (4) and 2 (5), respectively. If 1 is treated twice with 2 eq. of BuLi and then 2 eq. of SiMe2HCl, a further pentasilylated compound, [C5(SiMe3)(SiMe2H)4]‐Mn(CO)3 (6), is obtained. In situ chlorination of [C5(SiMe2H)5]Mn(CO)3 or 6 with PdCl2, followed by addition of MeMgCl, yields after chromatography an inseparable mixture of [C5(SiMe3)4X]Mn(CO)3 compounds, where X = H (7a), SiMe2H (7b), and SiMe3 (7c).
Metallkomplexe mit funktionalisierten Schwefel‐Liganden, VI[1]. Stabilisierung von 1‐Alkin‐1‐thiolato‐Liganden [R–C≡C–S–; R = SiMe3,(η5‐C5H4)Fe(η5‐C5H5)] in Ru(II)‐ und Pt(II)‐Komplexen. Kristallstrukturanalyse von cis‐(Ph3P)2Pt[C≡C–(η5C5H4)Fe(η5‐C 5H5)]2
Authors: Weigand Wolfgang , Robl Christian 
Published: July 2007

Metal Complexes of Functionalized Sulfur‐Containing Ligands, VI[1]. – Stabilization of 1‐Alkyne‐1‐thiolato Ligands [R–C≡C–S–; R = SiMe3, (η5‐C5H4)Fe(η5‐C5H5)] in Ru(II) und Pt(II) Complexes. X‐ray Structure Analysis of cis‐(Ph3‐P)2Pt[C≡C–(η5‐C5H5)]2The 1‐alkyne‐1‐thiolates R–C≡C–SLi [1: R = SiMe3, 3: (η5‐C5H4)Fe(η5‐C5H5)] react with (Ph3P)2PtCl2 and CpRu(PPh3)2Cl to give the complexes trans‐(Ph3P)2Pt(S–C≡C–SiMe3)2 (4a), CpRu(PPh3)2(S–C≡C‐SiMe3) (4b), and cis‐(Ph3P)2Pt[S–C≡C–η5‐C5H4)Fe(η5‐C5H5)]2 (5). The Pt(II) bis(acetylide) complex cis‐(Ph3P)2Pt[C≡C–(η5‐C5H4)Fe(η5‐C5H5)]2 (6a) was isolated after chromatography of 5. The trans‐configurated compound 6b is obtained by the reaction of [LiC≡C–(η5‐C5H4)]Fe(η5‐C5H5) with (Ph3P)2PtCl2. The complexes are characterized by IR, 1H‐, 13C‐, and 31P‐NMR spectroscopy, FAB mass spectrometry and X‐ray diffraction (6a).
Small Rings, 76[1]. – Intermediates on the Way to Tetramethyl Cyclopentadienonetetracarboxylate
Authors: Maier Günther , Wilmes Rolf 
Published: July 2007

Abstract„Potassium salt”︁ 6, already described by Cookson, reacts with suitable electrophilic reagents to yield the enol esters 8–10. A base‐catalyzed acylation of the hydroxy group in 8–10 cannot be achieved because deprotonation is immediately followed by a [1,5] ester migration. The same reaction occurs upon heating 8–10 to 80°C, leading to the 1,3‐keto enols 11, 12, and 14. Upon treatment of „alcohol”︁ 7 with acetyl chloride only the dimer 3 of cyclopentadienone 2 can be isolated.
Kleine Ringe, 77[1]. Erzeugung und Abfangreaktionen von Cyclobutadientetracarbonsäure‐tetramethylester
Authors: Maier Günter , Wilmes Rolf , Fuchs Hansjörg , Leinweber Matthias 
Published: July 2007

Small Rings, 77[1]. – Generation and Trapping Reactions of Tetramethyl CyclobutadienetetracarboxylateDibromocyclobutane derivates 6 and 7 serve as precursors for the generation of the title compound 1. In the presence of suitable reagents 1 can be trapped in Diels‐Alder additions. Photocyclization of the adducts can be used for the construction of polyfunctionalized cage compounds.
Cycloadditions, 43[1]. Cyclobutanones via Photoreactions of Chromium‐Carbene Complexes with Olefins and Dienes – A Comparison with the Traditional Ketene Method
Authors: Köbbing Stephan , Mattay Jochen , Raabe Gerhard 
Published: July 2007

AbstractPhotolysis of chromium‐carbene complexes 1 in the presence of olefins and dienes yields cyclobutanones 4 and 5 with varying stereoselectivity. Under oxidative conditions lactones 6, 7, 8, and 10 are obtained as byproducts. Thermal reactions of ketenes 3 with olefins and dienes yield the same cyclobutanones with usually equal selectivities. In the case of 2,3‐dihydro‐1,4‐dioxin as olefin, diene 9 is obtained as a byproduct. Cycloaddition reactions of 1a or 3a with 1,2‐dimethylenecyclopentane (11) yield the spirocyclic cyclobutanones 12 and 13. The symmetric ketone 16 and the ketene dimer 17 are formed as additional products upon cycloaddition of ketene 3b to tetraethoxyethylene. Novel α‐(butylthio)cyclobutanones 4j, k, l, m and 5k, l are formed by cycloaddition reactions of the newly prepared compounds 1c and 3c. The ketene dimer 20 is formed by thermal reactions of 3a with olefins. Unusually low stereoselectivities are observed in the case of photolytic reactions of 1c with dienes.
α‐Oxygen‐Substituted Organolithium Compounds and their Carbenoid Nature: Reactions with RLi and Other Nucleophiles, Experimental and IGLO‐Calculated 13C‐NMR Shifts of the Carbenoid C Atom
Authors: Boche Gernot , Bosold Ferdinand , Lohrenz John C. W. , Opel Achim , Zulauf Peter 
Published: July 2007

AbstractIn addition to the earlier[1] demonstrated C–O bond elongation between the anionic carbon atom and oxygen in α‐lithiated ethers which indicates a carbenoid character of these compounds we provide further evidence for this property in this publication. Thus, α‐lithiated ethers RCH(Li)–OR' react as electrophiles with nucleophiles R' Li to give RCH(Li)–R' + LiOR', and the 13C‐NMR signal of the carbenoid C atom is shifted downfield (compared to the 13C signal of the corresponding non‐lithiated compound). Since the latter two observations are also made in the Li/Hal carbenoid series, α‐lithiated ethers indeed are Li/oxygen carbenoids. Furthermore, for the first time we have calculated the 13C shifts of carbenoid C atoms in the Li/oxygen carbenoid series by means of the IGLO method: the calculated data agree nicely with the experimental ones. They even allow the preferred bridged structure in solution to be determined.
Dihydroselenapyrans by [4 + 2] Cycloaddition of Diaryl Selenoketones
Authors: Hock Regina , Hillenbrand Stefanie , Erker Gerhard , Krüger Carl , Werner Stefan 
Published: July 2007

AbstractThe phosphorus ylides Ph3PCAr1Ar2 5 [Ar1 = Ph, Ar2 = 4‐CH3C6H4 (c); Ar1 = Ar2 = Ph (d); 4‐ClC6H4 (e); 4‐FC6H4 (f); 3‐CF3C6H4 (g); Ar1 = Ph, Ar2 = 4‐ClC6H4 (h)] were allowed to react with elemental selenium at ca. 75°C in toluene in the presence of an excess of 2,3‐dimethylbutadiene. The diaryl selenoketones 1 thus generated in situ by means of the „Staudinger chalcogenation”︁ reaction were trapped by the added conjugated diene to give the 2,2‐diaryl‐3,6‐dihydro‐4,5‐dimethyl‐2H‐selenapyrans 7 in high yield. Similarly, the ylides 5c–f and 5h were treated with selenium, and the resulting diaryl selenoketones 1 added to 1,3‐butadiene to give the corresponding 2,2‐diaryl‐3,6‐dihydro‐2H‐selenapyrans 8. Selenobenzophenone, synthesized analogously, was employed in a [4 + 2] cycloaddition reaction with 2,3‐dimethoxybutadiene to yield 3,6‐dihydro‐4,5‐dimethoxy‐2,2‐diphenyl‐2H‐selenapyran (9), which was characterized by an X‐ray crystal structure analysis. Compound 9 crystallizes in the space group P21/n. In the crystal the dihydro‐2H‐selenapyran adopts a distorted half‐chair conformation.