bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Stereochemistry of Diepoxynaphthacenes and Tetraepoxyheptacenes
Authors: Meier Herbert , Rose Bernd 
Published: July 2007

AbstractCycloaddition reactions of 1,4‐dihydro‐1,4‐epoxynaphthalenes (2) and benzo[c]furans (4), generated in situ from the tetracyclone adducts of 2, yield the diepoxynaphthacenes 5 (Schemes 1, 2). Out of 4 possible stereoisomers an exo‐exo and an exo‐endo geometry (A and C in Scheme 3) can be realized. The ratio A:C varies from pure A to pure C depending on the substituents of 2 and 4. Stereoisomeric heptacenes 7 can be obtained by a twofold cycloaddition of the same type (Scheme 4). Only one π bond of reactive alkynes such as cyclooctyne or acetylenedicarboxylate is capable of an addition to 4 (Schemes 5, 6).
Photochemical Formation of Heteromethylenecyclopropanes, 27. Annulated Tetrazolium Salts
Authors: Quast Helmut , Balthasar Jürgen , Fuss Andreas , Nahr Uwe , Nüdling Wolfgang 
Published: July 2007

AbstractLithiation of the annulated tetrazoles 6a, c with butyllithium yields the N‐lithiotetrazoles 7a, c which are allowed to react with alkyl halides. Alkylation at the α‐carbon atom is observed in the reaction with methyl iodide (→ 6b, d), 1‐bromo‐2‐chloroethane (7c→14a), and 1,3‐dibromopropane (→ 16, 17), while 1,2‐dichloro‐ and 1,2‐dibromoethane give other products, viz. 11–13. Quaternisation of 6 with dimethyl sulphate affords mixtures of 1‐methyl‐ (1) and 2‐methyltetrazolium salts (8) (3:1–4:1) from which the hexafluorophosphates 1 PF6 are obtained by crystallisation. Methyl triflate converts the ω‐azidonitriles 9 into the N‐methylnitrilium triflates 10 which immediately undergo an intramolecular 1,3‐dipolar cycloaddition to afford the 1‐methyltetrazolium triflates 1 F3CSO3. Cyclisation of 16 by intramolecular N‐alkylation furnishes the bisannulated tetrazolium bromide 3a · Br. Attempts to obtain the lower homologue 15, either from 14a or from 17, met with failure. Instead, 17 rearranges via 15b into 14b. The α‐branched tetrazole 24 is synthesised from ethyl cyanoacetate and the bromide 18. Double cyclisation of 24 affords the bisannulated tetrazolium chloride 3b · Cl. The analogous scheme, envisaged for the synthesis of the lower homologue 32, failed in the last step owing to the high strain of this system.
A Novel Synthesis and the Autoxidation of 2,4,6,8‐Tetraphenylbarbaralane
Authors: Quast Helmut , Becker Christian , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg 
Published: July 2007

AbstractAddition to the diphenyldiketone 11 of the reagent prepared from rigorously dried cerium(III) chloride and phenyllithium yields the tetraphenyldiol endo,endo‐13 after extended periods of time. The configuration of this diol, which was previously assigned the (incorrect) configuration exo,exo‐13, is established by an X‐ray diffraction analysis. Dehydration of endo,endo‐13 with sulphuric acid in acetic acid affords a mixture of the oxatwistane 16 and the tetraphenyldiene 17 (3:1). Only the latter is obtained from endo,endo‐13 by the action of boron trifluoride–diethyl ether in dichloromethane solution. While attempts at allylic bromination of 17 with N‐bromosuccinimide in conventional solvents inevitably lead to complete decomposition, use of cyclohexane as solvent allows to obtain solutions of allylic dibromides that can be cyclised with the zinc‐copper couple to afford tetraphenylbarbaralane 9 in 58% yield based on 17. Thus, 9 is now available from the diphenyldiketone 11 in only three steps with an overall yield of 42%. – The autoxidation of 9, studied in various solvents, yields mixtures of products of which the epoxyendoperoxides 20 and 21, the unsaturated ketone 22, and a labile, probably oligomeric or polymeric product C are isolated in pure form. The structures 21 and 22 are elucidated by X‐ray diffraction analysis and independent synthesis, respectively. On warming, 20 rearranges into 21. Traces of acid convert the unknown autoxidation product A instantaneously into the unsaturated ketone 22. – Rate studies show that the autoxidation of 9 starts after a short initiation period. 2,6‐Di‐tert‐butyl‐4‐methylphenol exhibits powerful inhibitory effects. These results demonstrate the free radical nature of the autoxidation of 9. – The results are interpreted in terms of a mechanistic scheme involving initiation of the radical chain by addition of triplet oxygen to 9 to generate the diradical 28 followed by a radical chain 1:1 copolymerisation of 9 and oxygen to produce diradical 29. Eventually, endo addition of oxygen to 29 gives rise to the formation of the epoxyendoperoxides 20 and 21. Intramolecular hydrogen abstraction from the methylene group (C9) is accompanied by cleavage of a bridgehead bond (C1–C2) and the adjacent O–O bond to afford the extremely labile product A (perhaps 32 or 33) which undergoes acid‐catalysed elimination to furnish ketone 22.
Methylchalcogen Derivatives of 1,4,5,8‐Tetrathiatetralin
Authors: Nakatsuji Shin'Ichi , Amano Yoshiki , Kawamura Haruki , Anzai Hiroyuki 
Published: July 2007

AbstractTetrakis(methylthio)‐ and tetrakis(methylseleno)‐1,4,5,8‐tetrathiatetralin 3 and 4 were prepared by the reaction of tetrathiatetralin 2 with LDA (lithium diisopropylamide) and MeS‐SMe or MeSeSeMe in diethyl ether. A remarkable solvent effect was observed in that the similar reaction in tetrahydrofuran gave tetrakis(methylthio)tetrathiafulvalene 5 through a novel rearrangement. The iodine complex of 3 was prepared to be a rare example of complex formation in the tetrathiatetralin series.
Ozone Chemistry of Acetylenes: Trapping of α‐Oxo Carbonyl Oxides by Methanol and Stabilization of α‐Oxo Hydroperoxides by Derivatization
Authors: Griesbaum Karl , Dong Yuxiang 
Published: July 2007

AbstractOzonolyses of four symmetrically substituted (13a–13d) and of four unsymmetrically substituted acetylenes (17a–17d) gave all of the expected α‐oxo methoxyhydroperoxides (14a–14d, 18ae–18de, 19ae–19de) with good selectivities. The labile, non‐isolable hydroperoxides were converted into the corresponding O‐methyl oximes (15, 18f, 19f), which could be isolated as stable compounds.
Azo Bridges from Azines, XXIV. Tuning the Addition of Thiols to Parallel CC/NN Bonds from Transannular to Normal Addition
Authors: Hünig Siegfried , Brand Uwe , Peters Karl , Prokschy Frank , von Schnering Hans Georg 
Published: July 2007

AbstractAs an example of system A, compound 5 was reacted with several thiols. A radical route procedures transannular 1,4‐addition products (6a/b). In the presence of sulfur, the addition reaction is strongly enhanced, and a polar route yields 1,2‐adducts (7a/b). Structures 6a/b and 7a/b are supported by X‐ray analysis. The different reaction modes are discussed.
Pheromone Synthesis, CLXXXI. Synthesis of the Racemate and the Enantiomers of (Z)‐7,15‐Hexadecadien‐4‐olide, the Sex Pheromone of the Yellowish Elongate Chafer, Heptophylla picea
Authors: Nakayama Tôru , Mori Kenji 
Published: July 2007

Abstract(4R,7Z)‐7,15‐Hexadecadien‐4‐olide (1), the female‐produced sex pheromone of the yellowish elongate chafer (Heptophylla picea), was synthesized by lipase‐catalyzed resolution of (±)‐10. The racemate and the opposite (S)‐enantiomer of the pheromone were also synthesized. Both (R)‐1 and (±)‐1 showed the pheromone activity.
A Hetero Retro Diels–Alder Reaction in Aqueous Solution: A Dramatic Water‐Induced Increase of the Equilibrium Constant and Inhibition of Cycloreversion
Authors: Wijnen Jan W. , Engberts Jan B. F. N. 
Published: July 2007

AbstractThe adduct of the Diels–Alder reaction of nitrosobenzene with cyclopentadiene is not stable in solution. The equilibrium constant for the reaction depends strongly on the medium and water induces a spectacular shift to the adduct. Comparison with the bimolecular addition of nitrosobenzene to 1,3‐cyclohexadiene enables separation of the effect of the aqueous medium on the rate constants for the forward and reverse reaction. In water, the former reaction is accelerated and the latter is retarded. The deceleration of the retro reaction in water is due to hydrogen‐bond stabilization of the adduct. The influence of cosolvents and micelles on the cycloreversion is discussed.
First Total Synthesis of (+)‐Membrine
Authors: Wirth Thomas 
Published: July 2007

AbstractThe easily accessible, optically active diselenide 1 is converted into the chiral selenium electrophile 2 and used for oxyselenenylation reactions of alkenes with functionalized nucleophiles. This reaction allows the synthesis of addition products 4, 6 and 10 with the selenium functionality as precursors for an intramolecular radical cyclization. This strategy is applied to the first total synthesis of optically pure (+)‐membrine (13) by a short synthetic sequence.
Band‐Shaped Structures by Repetitive Cycloaddition Reactions of Benzo[1,2‐b:4,5‐b′]bisthiete
Authors: Meier Herbert , Rose Bernd , Schollmeyer Dieter 
Published: July 2007

AbstractBenzo[1,2‐b:4,5‐b′]bisthiete (1) undergoes stepwise thermal opening of the 4‐membered rings, thereby generating two highly reactive 8π systems (Scheme 1). In the presence of 1,4‐dihydro‐1,4‐epoxynaphthalenes 2, the dithiaheptacene derivatives 3 are formed, dehydration of which leads to the compounds 4 and 5 (Scheme 2). Repetitive cycloaddition reactions of 1 with the twofold 2π component 11 (Scheme 3) yield the oligomers 15 with statistically bent (and possibly cyclic) structures (Schemes 4 and 5). While 15 and the related oligomers 14 are freely soluble in many organic solvents, the dehydrated systems 16 (Scheme 6) are totally insoluble.
Diradical Wells, IX. Stereochemistry of Cyclopropane Ring Opening: The Case of 1,1‐Difluoro‐2,3‐diphenylcyclopropane
Authors: Roth Wolfgang R. , Wasser Thorsten , Boenke Martin 
Published: July 2007

AbstractFrom the O2‐dependence of the trapping rate of 1,1‐difluoro‐2,3‐diphenylcyclopropane in supercritical CO2 in the temperature range 110–180°C and the rates of its geometrical isomerization and racemization of the trans‐isomer, the energy profile for the geometrical isomerization is derived. Assuming that 7 is a common intermediate, the temperature dependence of the ratio of the rates of isomerization/racemization leads to a lowering of 1.2 kcal · mol−1 for the activation energy for the disrotatory cyclization of the intermediate diradical compared to the conrotatory mode. The energy barriers associated with cyclization of the diradical amount to 2.1 and 0.9 kcal · mol−1, respectively.
Geminal Substituent Effects, 15. Enthalpies of Formation of a Series of Fluorinated Hydrocarbons and Strain‐Free Group Increments to Assess Polar and Anomeric Stabilization and Strain
Authors: Schaffer Frank , Verevkin Sergey P. , Rieger Hans‐Jürgen , Beckhaus Hans‐Dieter , Rüchardt Christoph 
Published: July 2007

AbstractEnthalpies of combustion, ΔH, and enthalpies of vapourization, ΔH, for nineteen fluorohydrocarbons containing the groups CF, CF2, and CF3 were measured calorimetrically. From these data, enthalpies of formation, ΔHf(g), were calculated and were partitioned into new strain‐free group increments of the Benson and v. Schleyer type: CH3[F] = −42.1; CH2[F, C] = −37.1; CH[F, 2 C] = −35.7; C[F, 3 C] = −39.6; CH2[2 F] = −61.0; CH[2 F, C] = −71.7; C[2 F, 2 C] = −67.3; CH[3 F] = −110.8; C[3 F, C] = −131.4; C[4 F] = −150.4; F[C] = −195.7 kJ mol−1. These increments now allow the calculation of the enthalpies of formation of a large family of homologous fluorohydrocarbons. Fluorine substitution, in general, stabilizes saturated hydrocarbon structures. A new concept, which was proposed recently for ethers, acetals, ketals, and orthoesters, for the analysis of the values of the increments for CH3, CH2, CH, and C groups with their different neighbouring atoms (given in brackets), is successfully applied to fluorohydrocarbons. In this method, the number of pairwise geminal interactions XCY between all attached atoms X and Y is counted. The anomeric stabilization in geminal difluoromethylene groups taken from the FCF interaction is found to be 8 kJ mol−1 smaller than the OCO interaction for acetals and ketals, in agreement with calculations in the literature.
Synthesis of Novel C2‐Symmetrical Diamino Thioethers Derived from Amino Acids
Authors: Christoffers Jens 
Published: July 2007

AbstractChiral β‐amino alcohols 2, available from natural α‐amino acids by reduction, have been converted in a sequence of N‐protection, O‐activation, thioether formation, and deprotection to novel C2‐symmetrical β,β′‐diamino thioethers 1, which shall serve as chiral tridentate ligands in late transition metal complexes. Optical purity of compounds 1 was established by amide formation with (+)‐O‐acetylmandelic acid.
Diels‐Alder Reactions of Tetradehydrodianthracene with Electron‐Deficient Dienes
Authors: Sauer Jürgen , Breu Josef , Holland Uwe , Herges Rainer , Neumann Helfried , Kammermeier Stefan 
Published: July 2007

AbstractTheoretical calculations and simple MO considerations predict that a coplanar and spatially close arrangement of double bonds in structures such as tetradehydrodianthracene 1, should both lower the LUMO and raise the HOMO energy of the π system. Thus the reactivity in Diels‐Alder reactions towards electron‐rich, as well as electron‐deficient, dienes should be enhanced. The first effect has already been shown in a previous paper, the latter statement is now also confirmed by the reactivity of 1 in Diels‐Alder reactions with inverse electron demand. In [4 + 2] cycloaddition reactions of 1 with 1,2,4,5‐tetrazines 2 the electronic effect of 3,6 substituents in tetrazines is far outweighed by steric factors resulting in an unexpected reactivity sequence: 2a ≫ 2b ≈ 2c > 2d.
Cyclophanes, XLI. Cyclophanes as Precursors for Saturated and Unsaturated Cage Hydrocarbons – the Catalytic Hydrogenation of [2.2]Paracyclophane
Authors: Hopf Henning , Savinsky Rainer , Jones Peter G. , Dix Ina , Ahrens Birte 
Published: July 2007

AbstractThe catalytic hydrogenation of [2.2]paracyclophane 1 has been reinvestigated with the following results: a) Best yields (95%) of the perhydrocyclophane 3 are obtained when 1 is hydrogenated over ruthenium on charcoal in ethanol at 200°C and 300 atm in the presence of lithium hydroxide; b) hydrogenation of 1 in ethyl acetate/acetic acid over platinum at room temperature and normal pressure leads to the monoene 7 and one diene, to which we assign structure 11 since dichlorocyclopropanation converts it to the bis‐adduct 12, whose structure was determined by X‐ray structural analysis; c) when the tetraene 13 (prepared from 1 by Birch reduction) is hydrogenated over palladium on charcoal in petroleum ether, the triene 14 is obtained in addition to the dienes 4 and 11. Again, dichlorocyclopropanation followed by X‐ray structural analysis of the resulting tris‐adduct 17 was employed for the structure determination of the hydrocarbon precursor. The strain energies of the anti‐Bredt hydrocarbons 11 and 17 have been calculated by molecular mechanics calculations.
Thermal Rearrangements, 28. Competing Reaction Pathways in the Thermal Cycloisomerization of 1,3‐Hexadien‐5‐ynes
Authors: Nüchter Uta , Zimmermann Gerhard , Francke Viola , Hopf Henning 
Published: July 2007

AbstractThe thermal cycloisomerization of the 1,3‐hexadiene‐5‐ynes 1a–e has been studied at temperatures above 500°C and reaction times of about 0.3 s (1a–d) and at a pressure of 1.5 · 10−2 Torr (FVP, 1e), respectively, at low partial pressures in quartz flow systems. While 1a and 1b cycloisomerize exclusively to the corresponding benzenes and pentafulvenes, substrates 1c–e cyclize primarily to 4‐substituted 1,2‐dihydronaphthalenes and biphenyls. The experimental results suggest a predominance of unimolecular reactions such as electrocyclic ring closures and 1,6‐C,H‐insertion processes of alkenylidene carbenes initially formed by an acetylene→vinylidene rearrangement.
An Improved Synthesis of 1,3,3‐Trimethyl‐2‐azabicyclo[2.2.2]octane and Its Nitroxyl Radical Product, a Rigid Analogue of TEMPO
Authors: Bakunov Stanislav , Tkachev Alexey 
Published: July 2007

AbstractA new synthetic approach for the production of isoquinuclidine 6 from dipentene (rac‐limonene, 1) is described. The nitroxyl 5, a rigid analogue of TEMPO, has been prepared from 6 in 87% yield.
Solanum Alkaloids, 139 – Photolysis of N‐Chlorospirosolanes
Authors: Quyen Le Thi , Himmelreich Uwe , Schreiber Klaus 
Published: July 2007

AbstractUV irradiation of N‐chlorosoladulcidine (2) in trifluoroacetic acid, followed by separation and hydrolysis of the obtained 3‐O‐trifluoroacetates affords (23R)‐23‐chlorosoladulcidine (5) and 23,23‐dichlorosoladulcidine (7). Similar treatment of N‐chlorotomatidine (9) affords 23,23‐dichloro‐22‐isotomatidine (12).
Synthesis and Aggregation Behavior of Cyclic Single‐ and Double‐tailed Phosphate Amphiphiles: A Novel Class of Phosphate Surfactants – Comparison with the Aggregation Behavior of Sodium Di‐n‐Alkyl Phosphates
Authors: Buwalda Rixt T. , Wagenaar Anno , Engberts Jan B. F. N. 
Published: July 2007

AbstractHerein we describe the synthesis and aggregation of the sodium salts of a series of 5‐alkyl‐2‐hydroxy‐1,3,2‐dioxaphosphorinan‐2‐ones and 5,5‐dialkyl‐2‐hydroxy‐1,3,2‐dioxaphosphorinan‐2‐ones in aqueous solution. The results are compared with properties of previously studied sodium di‐n‐alkyl phosphates. The single‐tailed surfactants (6a, b, g) form micelles whereas the double‐tailed ones (6f, h–k) form vesicles, as revealed by transmission electron microscopy (TEM). Critical micelle concentrations (CMC) for 6a, b, g were determined using different techniques: UV spectroscopy, microcalorimetry, and conductometry. Phase transition temperatures of the bilayers were measured by differential scanning calorimetry (DSC) and by fluorescence depolarization. Fusion of the vesicles was studied employing the resonance energy transfer (RET) assay based on lipid mixing and TEM. Vesicles of 6h–k fuse upon addition of Ca2+ or Mg2+ ions, to almost the same extent in each case. Fusion only takes place above the phase transition temperature (Tc) of the different bilayers. The threshold concentrations of Ca2+ and Mg2+ ions for fusion of the different vesicles are below 0.1 mM. The initial rate of fusion is high and precludes the measurement of accurate rate constants. Upon addition of calcium chloride different processes occur. Vesicle fusion, crystallization, and formation of multilamellar sheets were observed, as was apparent from experiments with vesicles formed from 6h. Leakage through the vesicular bilayer of 6h was determined by measuring the carboxyfluorescein release from the aqueous compartment of the vesicles. All data are consistent with the notion that the alkyl chain packing in the bilayers of the vesicles formed from the cyclic phosphates is less efficient than that in the bilayers of vesicles composed of di‐n‐alkyl phosphates.
Chemistry of the Ginkgolides, IX. Ozonolysis of (10R)‐10‐Acetoxy‐3,14‐didehydroginkgolide
Authors: Weinges Klaus , Schick Hartmut , Irngartinger Hermann , Oeser Thomas 
Published: July 2007

AbstractOzonolysis of (10R)‐10‐acetoxy‐3,14‐didehydroginkgolide (1) did not lead to the expected α‐hydroxy ketone 3b. Instead, ring‐opening of the acetal ring C occurred leading, after acetylation, to the spiroacylal 2. Its structure was confirmed by crystal structure analysis.
Synthesis of New Pyropheophytin‐naphthoquinone Dyads for Investigations of Photoinduced Electron Transfer
Authors: Malinen Pasi K. , Tauber Andrei Y. , Helaja Juho , Hynninen Paavo H. 
Published: July 2007

AbstractTwo new, covalently‐linked pyropheophytin‐naphthoquinone dyads 1 and 2 have been synthesized for use as model compounds in studies of photoinduced electron transfer. The starting material for the synthesis was chlorophyll a (3). This was first pyrolyzed to 132‐demethoxycarbonylchlorophyll a (4), which was then oxidized regioselectively to 132‐demethoxycarbonyl‐P4(R/S)‐hydroxypheophytin a (5). Compound 5 was esterified with naphthoquinone carboxylic acid 17 by the carbodiimide method to afford 132‐demethoxycarbonyl‐P4(R/S)‐oxy‐[2‐(2′‐carboxyethyl)‐3‐methyl‐1,4‐naphthoquinone]pheophytin a (1) and (2). The observation that fluorescence emission is effectively quenched in dyads 1 and 2, relative to compound 5 which does not bear an electron‐acceptor, indicates that intramolecular electron transfer from the excited donor part to the ground state acceptor part of the molecule occurs readily.
Enzymatic alcoholyses of NAD: A New type of ADP‐ribosylation reaction catalysed by NAD glycohydrolase
Authors: Tono‐oka Shuichi , Azuma Ichiro 
Published: July 2007

AbstractAs part of studies concerning the transglycosidation action of NAD glycohydrolase, the hydrolase‐catalysed reaction of normal alkyl alcohols (six alcohols from methanol to 1‐hexanol) has been investigated. All the alcoholic substrates were found to undergo ADP‐ribosylation with varying efficiences, to give the corresponding O‐ribosylated products (1–6). Yields (11–67%) were dependent upon the solubility of the substrates in aqueous media and upon their inhibitory effect on the enzyme activity. 1H NMR analyses demonstrated the alkyl β‐riboside structure of compounds 1–6 and the non‐equivalence of the O‐methylene protons of their alkoxy groups. This is the first report of characterization of O‐ribosylated products formed by the transglycosidation action of NAD glycohydrolase.
Synthesis of a Central Intermediate in the Biosynthesis of Di‐ and Trideoxysugars
Authors: Müller Thomas , Schmidt Richard R. 
Published: July 2007

AbstractThe synthesis of disodium (6‐deoxy‐α‐D‐ribo‐hexopyran‐3‐ulosyl) (2′‐deoxythymidin‐5′‐yl) diphosphate (1) is described. To this end, D‐glucose is transformed into known furanose derivative 2 possessing a 3‐C‐methylene group as latent functionality for 3‐ulose generation. From 2, 3,6‐dideoxy derivative 6 was synthesized; ensuing acid catalyzed cleavage of the 1,2‐O‐isopropylidene group and then O‐acetylation furnished the required pyranose 8α,β, which could be selectively deacetylated at the anomeric oxygen to afford 9α,β. Treatment with phosphitylating agent 13e and then oxidation led to dibenzylphosphate derivative 15e which could be chemoselectively debenzylated by hydrogenolysis without affecting the olefinic double bond (→ 17); de‐O‐acetylation and then ozonolysis afforded the unprotected phosphate intermediates 18 and 19, respectively. Both compounds could be successfully used for the synthesis of 1 by employing the nucleoside phosphate morpholidate procedure for the generation of nucleoside diphosphate sugars. Ozone cleavage of the olefinic double bond in 20 could be successfully performed even in the presence of the thymine moiety.
Cyclophanes, XLII. The Acid‐Catalyzed Isomerization of Perhydro[2.2]paracyclophane – A Surprising Out‐In Hydrogen Transfer Process
Authors: Ernst Ludger , Hopf Henning , Savinsky Rainer 
Published: July 2007

AbstractTreatment of perhydro[2.2]paracyclophane (1) with trifluoromethanesulfonic acid for 15 h at room temperature in dichloromethane results in a quantitative yield of stereoisomer 2, in which one of the bridgehead hydrogen atoms points towards the inside of the molecule (mono‐endo isomer). The constitution of 2 is derived from 2D‐NMR C,C‐INADE‐QUATE experiments and its stereochemistry from dynamic NMR experiments and molecular mechanics computations (MM3). A mechanism is suggested for the 1–2 interconversion.
Calixarene Carbamates
Authors: König Burkhard , Fricke Tom , Dix Ina , Jones Peter G. , Thondorf Iris 
Published: July 2007

AbstractCalixarene carbamates were obtained in good yield from the clean reaction of n‐butyl isocyanate with para‐tert‐butyl‐calix[4]‐, ‐[6]‐, and ‐[8]arenes. Whereas the two larger calixarenes remain mobile in solution upon derivatisation, para‐tert‐butyl‐calix[4]arene is locked in the cone conformation. A selective triple acylation was observed with Li2CO3 as base, whereas K2CO3 leads to complete functionalisation of all hydroxy groups. The relative stability of all possible conformers of calix[4]arene tetracarbamate (1) was examined by force field calculations, showing the cone conformer as the most stable one. The structures of compounds 1 and 3 were investigated by X‐ray structure analysis, confirming the cone conformation for both compounds.