bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereoselectivity in reactions of metal complexes VII. Asymmetric synthesis of amino acids by metal ion‐promoted transamination
Authors: Bernauer Klaus , Deschenaux Robert , Taura Toshiaki 
Published: December 2004

AbstractEnantioselective synthesis of phenylalanine was performed by reacting phenylpyruvic acid with pyridoxamine followed by ketimine‐aldimine isomerization of the Schiff base formed catalyzed by an optically active copper (II)‐complex. By UV and CD measurements it was shown that the enantiomeric excess strongly depends on the reaction conditions and on the reaction time. In favorable cases it reached values up to 80%. The selectivity of the reaction is discussed on the basis of possible structures of the intermediate mixed ligand complex.
Food‐Related Applications of High‐Resolution NMR. PART II. Differentiation between natural and synthetic vanillin samples using 2H‐NMR
Authors: Toulemonde Bernard , Horman Ian , Egli Huldrych , Derbesy Michel 
Published: December 2004

AbstractDifferences in the distribution of deuterium at individual atomic sites in vanillin samples are revealed by 2H‐NMR measurements, and can be used to determine whether the sample is of natural or synthetic origin.
Practical Asymmetric Diels‐Alder Additions to Camphor‐10‐sulfonic‐Acid‐Derived Acrylates. Preliminary Communication
Authors: Oppolzer Wolfgang , Chapuis Christian , Kelly Martha J. 
Published: December 2004

AbstractStarting from (+)‐camphor‐10‐sulfonic acid (1) the chiral crystalline alcohols 3 and 11 were prepared in two steps. Lewis‐acid‐mediated [4+2]‐additions of their acrylates to 1,3‐dienes were studied. Notably, the crystalline acrylate 4 underwent TiCl2 (OiPr)2‐promoted Diels‐Alder addition to cyclopentadiene giving after recrystallization efficiently the pure (2R)‐adduct 5.
cis‐Bis(2‐Phenylpyridine)platinum(II) (CBPPP). A simple molecular platinum compound preliminary communication
Authors: Chassot Laurent , Von Zelewsky Alex 
Published: December 2004

AbstractThe deprotonated 2‐phenylpyridine forms a 2:1 chelate with platinum(II) in cis‐configuration, which exists as a dimer in a molecular solid.
Nucleophilic Addition to C,C‐Double Bonds. Part VIII. The standard enthalpies of formation of anti9,10‐10endo‐hydroxytricyclo [4.2.1.12,5]deca‐3,7‐dien‐9‐one and 9‐Oxatetracyclo [5.4.0.03,10.04,8]undec‐5‐en‐2‐one and kinetic data for the cyclization of the olefinic alcohol to the ether
Authors: Smeaton Alan A. , Steele William V. , Ramos Tombo Gerardo M. , Ganter Camille 
Published: December 2004

AbstractIn view of the significance of steric compression in the base‐catalyzed intramolecular cyclization of polycyclic olefinic alcohols, the standard enthalpies of formation of anti9,10‐10 endo‐hydroxytricyclo [4.2.1.12,5]deca‐3,7‐dien‐9‐one (1) and 9‐oxatetracyclo [5.4.0.03,10.04,8]undec‐5‐en‐2‐one (2) as well as the kinetics of the ether formation 1 → 2 were determined.
Voafrine A and Voafrine B, New Dimeric Indole Alkaloids from Cell Suspension Cultures of Voacanga africana Stapf
Authors: Stöckigt Joachim , Pawelka Karl‐Heinz , Tanahashi Takao , Danieli Bruno , Hull William E. 
Published: December 2004

AbstractThe structures of voafrine A and voafrine B, two novel dimeric indole alkaloids isolated from Voacanga africana Stapf cell suspension cultures, were established and the medium‐dependent formation of both alkaloids was investigated.
Transition Metal Complexes with Bidentate Ligands Spanning trans‐Positions. Part XIII. Preparation, properties and crystal and molecular structures of chlorocarbonyl‐2,11‐bis(diphenylphosphinophenyl) benzo[c]phenanthreneiridium (I) and trichlorocarbonyl‐2,11‐bis(diphenylphosphinomethyl) benzo[c]phenanthreneiridium(III)
Authors: Baumgartner E. , Reed F. J. S. , Venanzi L. M. , Bachechi Fiorella , Mura Pasquale , Zambonelli Luigi 
Published: December 2004

AbstractThe complex [IrCl3(CO)(1)](4,1=2,11‐bis (diphenylphosphinomethyl)benzo[c]phenanthrene) has been prepared by CuCl2‐oxidation of [IrCl(CO)(1)](2a). It is shown that the chlorine oxidation of 2a gives a mixture of products whose composition depends on the reaction conditions. The X‐ray crystal structures of 2a and 4 have been determined. The small conformational differences observed for the trans‐spanning ligand 1 in the two complexes are likely to be caused by the difference in Ir‐P bond lengths in square planar 2a and octahedral 4 (2.310(4) and 2.411(3) Å, respectively).
Die Acylierung von Acetylenen mit β, γ‐ungesättigten Säurechloriden. Eine neue Synthese von 5‐Cyclopentenonen
Authors: Karpf Martin 
Published: December 2004

The Acylation of Acetylenes with β,γ‐Unsaturated Acid Chlorides, A New Synthesis of 5‐Substituted 2‐CyclopentenonesThe acylation of acetylenes with α,α‐disubstituted, β,γ‐unsaturated acid chlorides under Friedel‐Crafts‐type conditions leads to 5‐substituted 2‐cyclopentenones. Phenols are formed with β,γ‐unsaturated acid chlorides bearing at least one α‐H‐atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α‐disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2‐cyclopentenones is applied to the synthesis of some spiro[4.4]nona‐ and spiro[4.5]deca‐2,6‐dienones.
Molecular Recognition in Anion Coordination Chemistry. Structure, Binding Constants and Receptor‐Substrate Complementarity of a Series of Anion Cryptates of a Macrobicyclic Receptor Molecule
Authors: Dietrich Bernard , Guilhem Jean , Lehn Jean‐Marie , Pascard Claudine , Sonveaux Etienne 
Published: December 2004

AbstractThe crystal structures of four anion cryptates [X− ⊂ BT‐6H+] formed by the protonated macrobicyclic receptor BT‐6H+ with F−, Cl−, Br− and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F−‐ion is tetracoordinated, while Cl− and Br− are bound in an octahedron of H‐bonds. The non‐complementarity between these spherical anions and the ellipsoïdal cavity of BT‐6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H‐bonds, each interacting with a terminal N‐atom of N. The formation constants of the complexes formed by BT‐6H+ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP2−, ADP3−, ATP4−, P2O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F−, Cl−, Br−, and N may be analyzed in terms of the crystal structure data. The cryptand BT‐6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.
Décomposition du percarbonate deO,O‐t‐butyle etO‐isopropényle en solution: Acétonylation des esters, acides et nitriles
Authors: Lalande Robert , Filliatre Claude , Villenave Jean‐Jacques , Jaouhari Rabih 
Published: December 2004

The Free‐Radical Decomposition ofO,O‐t‐Butyl andO‐Isopropenyl Peroxycarbonate in Solution: the Acetonylation of Esters, Acides and NitrilesThe free‐radical decomposition ofO,O‐t‐butyl andO‐isopropenyl peroxycarbonate in substratres possessing mobile H‐atoms (SH) consists mainly in an induced chain process leading to acetonylated derivatives of the solvent. Fairly good yields are obtained but teh acetonylation of functional substrates often gives mixtures of isomers.In the case of methyl acetate, the acetonylation occurs on the C‐atoms adjacent to the carbonyl (acylox moiety) and to the O‐atom (alkox moiety). However, the relative amounts of the isomeric products depend on the concentration of the peroxycarbonate solutions; at lowest concentration, methyl 4‐oxopentanoate (acyloxy moiety) is obtained selectively. It is assumed that the free radicals issued from the solvent are able to abstract H‐atoms of other molecules of solvent before adding to the double bond of the peroxycarbonate; the more the peroxycarbonate solution is diluted the more the transfers from the C‐atom adjacent to the carbonyl to the radicals adjacent to the O‐atom are favoured. In the case of methyl alkanoates, H‐transfers from the α‐C‐atoms to β‐radicals of teh acyloxy moiety may account for the orientation of the process. Owing to similar H‐transfer processes, the acetonylation of functional esters, of acids and nitriles is selective in most cases.
Molecular Ions of Transient Species: Vinylamine‐Cation
Authors: Albrecht Bruno , Allan Michael , Haselbach Edwin , Neuhaus Louis , Carrupt Pierre‐Alain 
Published: December 2004

AbstractVinylamine 1 was prepared by thermolysis of cyclobutylamine and its photoelectron spectrum was measured. I = 8.20 eV and I = 8.65 eV were found, the dominant vibrational progression (ṽ = 725 cm−1) indicating that in the course of 1(X)→1+(X̃) flattening around the N‐atom occurs. The Franck‐Condon profile of this band, however, suggests that a skeletal mode of ṽ ≈ 1400 cm−1 (observed also in the iso‐π‐electronic systems vinyl‐alcohol‐cation and allyl radical) may also be excited. Comparison with the data for the isomer acetaldehyde‐imine 2 and its cation s+ shows that the isomer couple 1/2 constitutes a further notable example for a relative thermochemical stability inversion on going from the neutrals to the cations.
Photoisomerization pathways of 8,16‐methno[2.2]metacyclopane‐1,9‐diene. A model case for adiabatic electrocyclic ring closure in the excited singlet state
Authors: Wirz Jakob , Persy Gabriele , Rommel Erika , Murata Ichiro , Naksuji Kazuhiro 
Published: December 2004

AbstractThe title compound1bideally meets the theoretical requirements for the occurrence of an adiabatic photoisomerization in the lowest excited state (11b*) and, indeed, the predominant primary photoreaction observed is the conversion to its fluorescent valence isomer 10b, 10c‐methano‐cis‐10b 10c‐dihydropyrene (11a*). The mechanism for the formation often previously observed photoproduct 8b, 9a‐dihydro‐9H‐ cyclopropa[e]pyrene (4a) has been analyzed in some detail (Scheme). Below − 30°C the reaction path consists of a three quantum process (two di‐π‐methane rearrangements and photochemical 1,7‐H shift) involving two thermally stable, but light‐sensitive isomers 8,11b‐methanocyclodeca[cde]naphthalene (2b) and 9H‐cyclohepta[def]‐phenanthrene (3b). At room temperature the rearrangement2b→4aproceeds with a single excitation step bypassing the ground state intermediate3b. Finally, upon prolonged irradiation of (4a), the methylene group is lost to yield pyrene. Compound2bcompletes the series of all possible adducts of methylene to a CC bond of pyrene.
Peduncularistin, Triabunnin und Aristolarin, drei neue Indolalkaloide aus Aristotelia peduncularis (LABILL.) HOOK. F., 191. Mitteilung über organische Naturstoffe
Authors: Kyburz Rolf , Schöpp Emanuel , Hesse Manfred 
Published: December 2004

Peduncularistine, Triabunnine and Aristolarine, Three Ne Indole Alkaloids from Aristotelia peduncularis (LLABILL.) HOOK, F.Peduncularistine (1), triabunnine (2) and aristolarine (3), three new indole alkaloids, have been isolated from Aristotelia peduncularis (LABILL.) HOOK. F.; the structure and absolute configuration of 1 were elucidated on the basis of spectroscopic data and confirmed byt transformation of 1 into aristeserratine (4), a known alkaloid isolated from the same plant. The proposed structure 2 for the second alkaloid and its absolute configuration were established but spectroscopic means and by partial synthesis from 4. The relative configuration of 3 was postulated on the basis of spectroscopic and biogenetic arguments.
The Synthesis and Reactions of 1‐(2‐Propynyl)pyidinium Salts
Authors: Katritzky Alan R. , Schwarz Otto A. , Rubio Olga , Markees Diether G. 
Published: December 2004

AbstractThe synthesis of 1‐(2‐propynyl)pyridinium salts 3 described. Compounds 3 react with a second pyridine molecule, in the presence of the corresponding hydrochloride, to form products of type 4, Certain bases cause the 1‐(2‐propynyl)pyridinium salts 3 to rearrange into 1‐propadienylpyridinium salts. 5. Diethylamine converts compounds 3 into 1‐acetonylpyridinium salts 8. Moreover, treatment of 3 or 5 with sodium methoxide gives enol ether sof type 9, which can be hydrolyzed to teh ketones 8. Addition of bromine to some of teh unsaturated compounds is also reported.
Integrated Systems for Water Cleavage by Visible Light; Sensitization of TiO2 Particles by Surface Derivatization with Ruthenium Complexes
Authors: Duonghond Dung , Serpone Nick , Grätzel Michael 
Published: December 2004

AbstractIrradiation of acidic (pH 2) solutions of RuL32+ 2Cl− (L = diisopropyl 2,2′‐bipyridine‐4,4′ ‐dicarboxylate) in the presence of TiO2 at 100°C leads to the loss of one bipyridyl ligand and the chemical fixation of RuL2 at the surface of teh TiO2 particles through formation of Ru‐O‐Ti bonds. These surface complexes are very stable and shift the absorption onset of TiO2 beyond 600 mm. Efficient sensitization H2‐generation is achieved with this system beginning in the wave length domain between 590 and 665 nm. Preliminary water cleavage experiments with bifunctional TiO2/Pt/RuO2 redox catalyst are reported.
Fluoro(phenylsufinyl)methyllithium. Note on the 13C‐NMR Spectrum of a Flourocarbenoid
Authors: Nájera Carmen , Yus Miguel , Hässig Robert , Seebach Dieter 
Published: December 2004

AbstractThe title compound is synthesized with 13C‐ and 6Li‐labelling on the fluorinated carbon atom. H/Li‐Exchange in fluoromethyl phenyl sulfoxide (1→2) causes a Δδ(13C) = + 11.4 ppm, a ΔJ(13C,1H) ≈ 0 Hz, and a ΔJ(19F,13C) = + 80.4 Hz. Tentative conclusions bout the struture of the title compound are drawn from these changes.
Studies on the Synthetic Usefulness of the Nitro Function. Part I. A Novel Cyclopentenone Ring Annelation
Authors: Nakashita Yoshihiko , Watanabe Toshio , Benkert Erwin , Lorenzi‐Riatsch Annalaura , Hesse Manfred 
Published: December 2004

AbstractA novel cyclopentenone ring annelation reaction is described. The treatment of the nitro compound 13 with aqueous sodium hydroxide in the presence of a phase‐transfer catalyst furnished 14a in one step. Similar treatment of 7 led to 8, the reaction of which with t‐BuOK afforded 9a without purification in high yield.
Synthesis of 14‐Membered Lactones from Cyclooctanone
Authors: Aono Tetsuya , Hesse Manfred 
Published: December 2004

AbstractAs shown in the Scheme, 3‐(1‐nitro‐2‐oxocyclooctyl)propanal (1) prepared earlier from cyclooctanone was converted into the 14‐membered lactones 6 and 7. The aldehyde 1 was submitted to allylation to give 2 using allyltitnium or allylsilicon reagents. After lactonizatrion and transformation of the C,C‐double bond to an alcohol, 4 was translactonized under acidic conditions to form 5, from which 6 and 7 were prepared.
Photochemistry of 2‐Allyl‐3‐oxo‐2,3‐dihydro‐1H‐pyrrole‐2‐carboxyalates
Authors: Beyer Michael , Ghaffari‐Tabrizi Ramin , Jung Michael , Margaretha Paul 
Published: December 2004

AbstractOn acetone‐sensitized irradiation the title compounds 3a–c are converted to 2‐allyl‐3‐hydroxy‐1H‐pyrrole‐2‐carboxylates 4 in reasonable yields.
1,2‐Epoxycarotinoide 5. Mitteilung, Synthese von (S)‐1,2‐Epoxy‐1,2,7,8,7′,8′‐hexahydro‐Ψ, Ψ‐carotin ((S)‐1,2‐Epoxy‐1,2‐dihydro‐ζ‐carotin)
Authors: Arm Christoph , Pfander Hanspter 
Published: December 2004

Abstract1,2‐Epoxycarotenoids, Synthesis of (S)‐1,2‐Epoxy‐1,7,8,7′,8′‐hexahydro‐Ψ, Ψ‐carotene ((S)‐1,2‐Epoxy‐1,2‐dihydro‐ζ‐carotene)The synthesis of (S)‐1,2‐Epoxy‐1,2‐dihydro‐ζ‐carotene ((all‐E,S)‐1) using (E,E)‐farnesol (3) as starting material, and a Sharpless epoxidation as key step is described.
Deoxy‐nitrosugars 8th communication Convenient preparation of 1‐C‐nitroglycosyl chlorides. Halonitro ethers from hydroxy oximes
Authors: Meuwly Roger , Vasella Andrea 
Published: December 2004

AbstractPartially protected 4‐ or 5‐hydroxy‐sugar oximes were transformed into 5‐ or 6‐membered 1‐C‐nitroglycosyl chlorides, respectively, by reaction with NaOCl under phase‐transfer conditions. With the exception of the oxidation of the gluco‐derivative 1 giving the anomers 6 and 7, the reactions were completely diastereoselective.
Rearrangement of Derivatives of 1,3‐Dithian‐5‐amineinto Bicyclic 2‐Thiazolidines. Crystal Structures of cis‐ and trans‐1‐(2‐Aryl‐1,3‐dithain‐5‐yl)‐2‐thioureas and cis‐ and trans‐5‐Aryl‐3‐imino‐7,7a‐dihydro‐1H,3H,5H‐thiazolo[3,4‐c]thiazoles
Authors: Borgulya Janos , Daly John J. , Schönholzer Peter , Bernauer Kerl 
Published: December 2004

AbstractUnder conditions normally applied to transform thioureas into the corresponding carbodiimides, cis‐ and trans‐1‐(2‐aryl‐1,3‐dithian‐5‐yl)‐2‐thioureas 7 and 8 undergo a rearrangement to 5‐aryl‐3‐imino‐7,7a‐dihydro‐1H, 3H, 5H‐thiazolo[3,4‐c]thiazoles 9/10 with cis‐ and trans‐fused rings, respectively. The structures of these novel heterocycles were established by X‐ray analysis of compounds 9a, 9d, and 10d. The cis‐fused compounds 9 are the thermodynamically more stable ones. The stereochemical outcome of the rearrangement depends on the carbenium ion stabilizing capability of the aryl moiety and on the reagent system applied. With Ar = Ph, p‐Cl‐Ph, p‐O2N‐Ph, the reaction can be directed to deliver mainly either the cis‐thiazolothiazoles 9 or the trans‐thiazolothiazoles 10. With Ar = 5‐methyl‐4‐imidazolyl or p‐Me2N‐Ph, formation of the cis‐thiazolothiazoles (9a and 9b, resp.) is strongly favored independently of the reaction conditions, In contrast to it 2‐aryl analogs, (1,3‐dithian‐5‐yl)‐2‐thiourea 7g can be transformed into the carbodiimide 11. Under rigorous conditions, 11 also undergoes rearrangement to the corresponding thiazolothiazole 9g. Mechanisms explaining the above findings are discussed. Reaction of trans‐2‐phenyl‐1,3‐dithian‐5‐amine 6d with phosgene or trichloromethyl chloroformate gives the 5‐phenyl‐7,7a‐dihydro‐1H,3H,5H‐thiazolo[3,4‐c]‐thiazol‐3‐ones 12 and 13, whereas the amine 5g lacking an aryl substitutent forms the sable isocyanate 14. Compound 14 is transformed into the corresponding thiazolothiazolone 15 by refluxing in diglyme. Syntheses are described for the 1,3‐dithian‐5‐amines 5/6 and the thioureas 7/8 derived therefrom. The relative configuration of 7d and 8d was determined by X‐ray analysis. NMR data then allowed to assign the configurations of all compounds of types 7 and 8.
Metal complexes with macrocyclic ligands. Part XX. Influence of coordinated ligands onto the complexation rate of Ni2+ with 1,4,8,11‐tetraazacyclotetradecane
Authors: Wu Yi‐he , Kaden Thomas A. 
Published: December 2004

AbstractThe kinetics of the reaction between 1,4,8,11‐tetraazacyclotetradecane (Cy) and Ni2+ in the presence of series of ligands L = fluoride, acetate, glycolate, oxalate, malonate, succinate, methanetriacetate, 1,3,5‐cyclohexanetriacetate, tricarballylate, picolinate, glycinate, iminodiacetate, nitrilotriacetate. N,N′ ‐ethylenediiminodiacetate, ammonia, pyridine, ethylenediamine, 1,3‐propanediamine and diethylenetriamine were studied by pH‐static and spectrophotometric methods at 25° and I = 0.5. By analysis of the log k/log [L] and/or log k/pH profiles the resolved bimolecular rate constants K (Table 3) were determined using a non‐linear least‐square fitting procedure. Practically for all systems the rate constant K, describing the reaction between the 1:1 Ni2+ complex and the monoprotonated form of the macrocycle, was obtained. In some cases, however, also K and K were found. Since the experimental conditions were choosen so that NiL was mainly formed, the reactivity of NiL2 was generally not measurable. The effect of the number of coordinated donor groups in NiL and of the charge of NiL on K is discussed. Both effects seem to indicate that for the reaction between NiL and CyH+ first bond formation is not the rate‐determining step.
Triaziridines. Part III. Triaziridine, azimine, and triazene: A SCF study of the energy and structure of N3H3‐isomers
Authors: Nguyen Minh‐Tho , Kaneti Jose , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

AbstractThe portions of the N3H3 singlet potential energy surface corresponding to triaziridines (1), azimines (2) and triazenes (3) have been calculated by ab initio SCF using 3‐21G, 6‐31G, and 6‐31G** basis sets. Minima and transition states were located by force gradient geometry optimization. The most important computation results are: (1) Triaziridines (1): The configuration at the 3 N‐atoms is pyramidal. There are 2 stereoisomers, 1a and 1b. The c,t‐isomer 1a has less energy than the c,c‐isomer 1b. The 2 stereoisomerizations by N‐inversion hve rather high activation energies. The N,N bonds in 1 are longer and weaker (STO‐3G estimation) than in hydrazine. The N‐homocycle 1 exhibits less ring strain than the C‐homocycle cyclopropane or three‐membered heterocycles. (2) Azimine (2): All 6 Atoms are in the same plane. There are 3 stereoisomers, 2a, 2b, and 2c. The order of ground state energies is (Z,Z) < (E,Z) ≫ (E,E). The 2 N,N bond lengths correspond to multiplicity 1½. The electronic structure of 2 corresponds to a 1,3‐dipole with almost equal delocalization of the 4 π‐electrons over all 3 N‐atoms. The negative net charge at the central N‐atom is much less than that at the terminal N‐atoms. Azimines should behave as π‐donors in complexation with transition metals (3) Triazene (3): All 6 atoms are in the same plane. There are 2 stereoisomers, 3a and 3b. The order of ground‐state energies is (E) < (Z). The stereoisomerization proceeds as pure N‐inversion. N‐Inversion has a high energy barrier inversion at N(1) is faster than at N(2). One of the N,N bond lengths is typical for a double, the other for a single bond. The electronic structure of triazene 3 entails rather localized π‐ and p‐electron pairs at N(1),N(2) and at N(3). Triazenes should behave as p‐donors in complexation with transition metals. (4) ‐N3H3‐Isomers: The order of ground‐state energies is 3 < 2 < 1. The energy differences between these constitutional isomers are much larger than between the stereoisomers of each. The [1,2]‐H shifts for conversions of 2 to 3 and the [1,3]‐H shift for tautomerization of 3 have relatively high activation energies; both shifts can be excluded as modes of thermal, unimolecular transformations.
Benz[cd]indoles. Part III. A New Stereospecific Synthesis of Dihydrolysergic Acid and an Entry to 14‐Substituted Derivatives
Authors: Haefliger Walter E. 
Published: December 2004

AbstractA new convenient synthesis of dihydrolysergic acid is described, which allows the preparation of substituted derivatives, especially those with different substitutents in the aromatic ring. Starting from appropriately substituted 5‐nitro‐2‐tetralones, the synthesis leads via a tricyclic isonitrile to the indole‐ring closure as the last step, thus circumventing the troublesome protection/deprotection of the latter.
Total Synthesis of (±)‐Clovene. On the Stereoelectronic Requirements of the α‐Alkynone Cyclisation
Authors: Ackroyd John , Karpf Martin , Dreiding André S. 
Published: December 2004

AbstractThe synthesis of the sequiterpenoid tricyclic hydrocarbon (±)‐cleovene (1) by application of the α‐alkynone cyclisation is described. The starting bicyclic carboxylic acid 2 was obtained from ethyl 3‐methyl‐2‐oxocyclohexane‐1‐carboxylate by modified known methods (24%) and converted to the α‐alkynone 3 (86%). The thermolysis of 3 in the gas phase at 620° selectively produced the tricyclo[6.3.1.01,5] dodecenone 4 (80%) which was converted to 1 (37%) by conventional procedures. The selectivity of the α‐alkynone cyclisation is discussed in terms of the stereoelectronic requirements (coplanarity factor) of the carbene insertion. In order to throw further light on the importance of this factor, the (1‐adamantyl) alkynone 16 was synthesised from adamantane‐1‐carboxylic acid (78%) and subjected to thermolysis at 620°. Since this led to the tetracyclo[6.3.1.1.13,10.03,7]tridecenones 17 and 18 (together 72%), we conclude that the planar carbene insertion transition state, while preferred, is not a stringent requirement.