bluuebunny/crossref_metadata_2025 huggingface dataset:
Antibiotics from Gliding Bacteria, LXX Chondramides A–D, New Cytostatic and Antifungal Cyclodepsipeptides from Chondromyces crocatus (Myxobacteria): Isolation and Structure Elucidation
Authors: Jansen Rolf , Kunze Brigitte , Reichenbach Hans , Höfle Gerhard
Published: June 2010

As a result of the extension of our screening to strains of Chondromyces four new antifungal and highly cytostatic depsipeptides were isolated, the chondramides A (1) – D (4). Their macrocyclic structures comprise three amino acids and a polyketide, viz. alanine, N‐methyltryptophan, α‐methoxyl‐β‐tyrosine, and a 7‐hydroxytrimethyloctenoic acid. Thus, they were found to be closely related to a small class of cyclodepsipeptides including jaspamide, the geodiamolides, and neosiphoniamolide which all have been isolated from marine sponges.
Wavelength Control in the Photochemical Addition of Tricyclic [g]‐Fused 1‐Thiocoumarins or Coumarins to Alkenes Yielding Mono‐ and Bis([2 + 2]‐Cycloadducts)
Authors: Klaus Christian P. , Margaretha Paul
Published: June 2010

On long‐wavelength (>395 nm) irradiation in the presence of 2,3‐dimethylbut‐2‐ene the benzobis(thiinones) 6 and 7 afford 4:1 mixtures of cis‐ and trans‐fused monocycloadducts. Similarly, irradiation of thiinobenzopyrandione 8 affords 50% of a 4:1 mixture of cis‐ and trans‐fused monocycloadducts at the thiinone moiety and in addition further 50% of the cis‐fused monocycloadduct at the pyranone ring. Irradiation of 6–8 at shorter wavelength (>340 nm) in the presence of the same alkene furnishes mixtures of all bis(photocycloadducts), of which some were isolated by chromatography and analyzed by 1H‐NMR spectroscopy. – Mixed bis([2 + 2]‐photocycloadducts) of such molecules become easily accessible, as illustrated by the irradiation of benzobispyranone 9, first (>350 nm) in the presence of 2,3‐dimethylbut‐2‐ene and then (>300 nm) in the presence of isobutene.
Heterocumulenes, 9 Ethenedione Oxime: Photochemical Generation and Matrix‐spectroscopic Identification
Authors: Maier Günther , Reisenauer Hans Peter , Röther Bernd , Eckwert Jürgen
Published: June 2010

The title compound 2, a very close derivative of the still elusive ethenedione (1), was generated by photocleavage of the three different precursor molecules 7–9 in an argon matrix at 10 K. The structure elucidation of monoxime 2 is based on the comparison of the experimental and calculated IR spectrum.
Ethynediol: Photochemical Generation and Matrix‐spectroscopic Identification
Authors: Maier Günther , Rohr Christine
Published: June 2010

Irradiation of squaric acid (4) in an argon matrix at 10 K leads to ethynediol (dihydroxyacetylene) (1) via bis (hydroxyketenyl) 5 and deltic acid (6). The identification of 1 is based on the comparison between the experimental and calculated IR spectrum.
Synthesis of Medium and Large Ring Compounds, XLI Synthesis and Reactions of Optically Active Bridged Methyl Deoxyfuranosides
Authors: Tochtermann Werner , Mattauch Anne‐Katrin , Kasch Michael , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: June 2010

The resolution of the earlier reported racemic bridged methyl deoxyfuranosides 1 and 3 was achieved via fractional crystallization of the ephedrinium salts 2 or by column chromatography of the camphanoates 5. The absolute configurations of 1 and 3 were established by X‐ray structural analysis of the (S)‐α‐naphthylethylammonium carboxylate (+)‐4 and by correlation with the other enantiomerically pure compounds of this type. (+)‐3 was converted into the 2,5‐bridged altrose derivative (+)‐8.
Reaction of Chiral Nucleophiles with Pyridinium Compounds. Total Synthesis of the Indole Alkaloids (−)‐Isovallesiachotamine and (+)‐Vallesiachotamine
Authors: Amann Robert , Arnold Karen , Spitzner Dietrich , Snatzke Günther , Majer Zsuzsanna
Published: June 2010

The addition of the chiral nucleophiles Na‐2 and Li‐5 to pyridinium compounds 1 and the subsequent ring closure (Pictet‐Spengler cyclization) to indoloquinolizines 3a and 7b, respectively, proceed stereoselectively (d.e. for 3a: 54%; for 7b: ≥95%). Proof for the absolute configuration of these products is provided by their CD spectral data and the transformation of 7b into the indole alkaloids (+)‐vallesiachotamine [(Z)‐6] and (‐)‐isovallesiachotamine [(E)‐6].
Unsaturated Hetero Chains, V Synthesis, Structure, and Reactivity of Alkoxy‐substituted 2,4‐diazapentadienylium‐, 2,4,6‐Triazaheptatrienylium‐, and 2,4,6,8‐Tetraazanonatetraenylium Salts
Authors: Schulte Norbert , Fröhlich Roland , Hecht Jürgen , Würthwein Ernst‐Ulrich
Published: June 2010

The 1‐mono‐ and 1,ω‐dialkoxy‐substituted 2,4‐diazapentadienylium, and 2,4,6,8‐tetraazanonatetraenylium salts 3, 5, and 10 were synthesized by oxonium salt alkylation of the corresponding 1‐oxa‐3,5‐diazahexatrienes 1, of the 1‐oxa‐3,5,7‐triazaoctatetraenes 4, and of the 1‐oxa‐3,5,7,9‐tetraazadecapentaenes 7. The salts 3 and 10 are sufficiently stable to facilitate their isolation whereas salt 5 decomposes readily. For the synthesis of the alkoxysubstituted 1‐oxa‐3,5,7,9‐tetraazadecapentaenes 7 a new general pathway was developed, which involves the condensation of the salts 3 with the N‐acylamidines 6. The structural properties in the crystalline state were determined for the salts 3d and 10a as well as for the neutral compound 7a by X‐ray crystallography. All three compounds are characterized by non‐planar helical chains, much in contrast to their planar all‐carbon analogous polyenes and polymethinium salts. From the UV/Vis spectra we deduce that these compounds prefer non‐planar structures also in solution. All stable compounds were completely characterized by analytical and spectroscopic methods.
On the Homoconjugation Between Donor and Acceptor Fragments. Synthesis and Properties of Bishomosquaric Acid Derivatives
Authors: Gleiter Rolf , Doerner Thomas , Irngartinger Hermann
Published: June 2010

The tetraketone 3,3,6,6‐tetramethylcyclohexane‐1,2,4,5‐tetrone (11) and its congener bicyclo[3.2.2]nonane‐6,7,8,9‐tetrone (17) were synthesized by conventional procedures. The photoreaction of 11 and 17 with tetramethylethylene yields 3,3,4,4,7,7,10,10‐octamethyl‐2,5‐dioxabicyclo[4.4.0]dec‐1(6)‐ene‐8,9‐dione (22) and 4,4,5,5‐tetramethyl‐3,6‐dioxatricyclo‐ [6.3.2.02;7]tridec‐2(7)‐ene‐12,13‐dione (24), respectively. Both are formally diesters of a bishomosquaric acid. The interactions between the two nonconjugated diketone moities in 11 and 17 as well as between the donor and acceptor fragments in 22 and 24 were studied. X‐ray investigations of 11 and 17 show no deviation from the expected bond lengths and angles. In the case of 24 the distance between the carbon atoms of the donor and acceptor units is 2.39 Å, this is 0.11 Å shorter than the corresponding distance between the two acceptor units in 17. The PE‐spectroscopic investigations of 11 and 17 show a considerable interaction between the two acceptor units. This is concluded from the splitting of the PE bands (ca. 0.5 eV) of the four lone‐pair combinations. For 22 and 24 no interaction between the donor and acceptor part was detected by means of PE spectroscopy. The 13C‐NMR chemical data show a high‐field shift for the carbonyl carbon atoms in 11 and 17. These findings were substantiated by the investigation of the corresponding phenazine derivatives obtained from 11 and 17 by the reaction with o‐phenylenediamine. In the case of 22 and 24 a high‐field shift of the signals of the olefinic double bond was observed. The electronic absorption spectrum of 22 shows for the higher excited states a charge‐transfer contribution, whereas in the case of 24 a charge‐transfer contribution was already detected in the first excited state.
Syntheses with Nitriles, XCVIII Synthesis and Characterization of (Aminocyanomethylene)indandione and ‐pyrazolone Chromoionophores as Extractants for Alkali Metal Ions
Authors: Boila‐Göckel Andrei , Fabian Walter M. F. , Junek Hans
Published: June 2010

A new approach to dissociable chromoionophores 5, 6a–e, 7 and 8 by reaction of (dicyanomethylene)indandione 1 and (dicyanomethylene)pyrazolones 2a–e, respectively, with aminophenyl crowns 3 and 4 is described. The complexation constants were determined by 1H‐NMR spectroscopy. For the chromoionophores 5 and 6a–e bearing a benzo[15]crown‐5 moiety, Kc values between 1100 and 1900 were found, while the chromoionophores 7 and 8 bearing the N‐phenylaza[15]crown‐5 provided binding constants which are about twenty times lower. These differences depending on the nature of the crown (aza‐crown or benzo‐crown with the same ring size) are discussed by comparison with a series of known crowns and also on the basis of molecular modelling techniques. The ability of the chromophore 6a as extractant for sodium and potassium ions in its ionic form is shown.
Deamination Reactions, 57. Bicyclo[3.2.0]hept‐3‐yl→7‐Norbornyl Rearrangements
Authors: Kirmse Wolfgang , Siegfried Rainer
Published: June 2010

Bicyclo[3.2.0]heptane‐endo‐ and ‐exo‐3‐diazonium ions (15, 17) were generated by diazotization of the analogous amines (12, 14) as well as by photolysis of bicyclo[3.2.0]‐heptan‐3‐one tosylhydrazone (13). In contrast to solvolyses of the corresponding tosylates (8, 11), the dediazoniation reactions afforded 16–30% of 7‐norbornanol. By means of deuterium labels, the rearrangement was found to proceed by way of sequential 2,3‐H and 1,2‐alkyl shifts; a protonated spirocyclopentane 5[7] is not involved in this process. While the 2,3‐H shift is but moderately exo‐selective, nucleophilic capture of the 7‐norbornyl cation (3‐D‐2) occurs stereospecifically within the limits of detection.
Photocyclization of Styrylbenzo[a]quinolizinium Salts, 2. Efficient Synthesis of 6a‐Azonia[5]helicene Salts Utilizing Steric Interactions of Substituents
Authors: Sato Kiyoshi , Nakajima Kazuaki , Arai Sadao , Yamagishi Takamichi
Published: June 2010

The synthesis of a series of substituted 6a‐azonia[5]helicene salts 3d–j and 12a‐azoniabenzo[ghi]perylene salts 4d and 4g by photocyclization of the corresponding 2‐styrylbenzo[a]‐quinolizinium derivatives 2d–j is described. The product ratios of 3d–j and 4d–j depend on the steric hindrance between the two substituents in the 2‐ and 13‐positions of 3d–j. Debromination of bromo‐substituted azonia[5]helicene salts 3h–j with a phosphanenickel(0) complex in methanol leads to parent and monomethyl‐substituted azonia[5]helicene salts 3a, 3b, and 3k, which could not be prepared by photocyclization.
Highly Functionalized Tris‐(σ)π‐Homobenzenes — Nine‐Membered Ring Compounds with Special Substitution Patterns — En Route to cis,cis,cis‐2,5,8‐Cyclononatriene‐1,4,7‐trione
Authors: Person Georg , Keller Manfred , Prinzbach Horst
Published: June 2010

In the pursuit of the tris‐(σ)π‐homobenzene chemistry, the synthesis of potentially tri(hexa)podal, C3v‐symmetrical, polyfunctionalized 9‐membered ring systems is being explored. A rather “expensive” tris‐σ‐homobenzene (13b) is the starting material for the tris‐σ‐isomer (14b) from which 1,4,7‐trimethylene‐cyclononatriene (2), its tri(hexa)epoxides (18, 20) and triepoxytriketo derivative (19) are prepared through generally highly selective transformations. An alternative approach toward the C3v 2,5,8‐cyclononatriene‐1,4,7‐trione [4, C6H6(CO)3] starts from the relatively “cheap” all‐exo‐1,4,7‐cyclononatriene‐trioxide (32), relies on selective epoxide opening reactions, and is complicated by typical mediumring transanular cyclizations; the rather efficient six‐step sequence does not reach the stated goal but carries attractive preparative prospects. For a central intermediate in each approach (trimethylenetrioxide 18 and bromo‐hydroxy‐diepoxycyclononane 50), X‐ray structural data are presented.
Azo Bridges from Azines, XVIII. Transformation of CC Bonds into Cyclopropanes, Aziridines and Oxiranes in the Presence of Azo Groups
Authors: Hünig Siegfried , Schmitt Michael
Published: June 2010

Rigid systems of typeBin which a three‐membered ring and an azo group are located in a rigid close and parallel position were synthesized by variation of both the hetero group X and the carbocyclic framework. Both the cyclopropane (X = CH2) and the aziridine (X = N‐R) moieties are introduced by [3 + 2] cycloaddition reactions of diazomethane (1,15,18,20) or azides (26/1–5,35,38,41,44) to CC‐double bonds and subsequent denitrogenation of the cycloadducts. By thermal and photochemical (300 nm) denitrogenation the triazolines were smoothly transformed into the expected aziridines (27/1–5) whereas catalysis by silica gel party caused additional rearrangements (28,37,40,43,46). Chemoselective photo‐denitrogenation of azo/pyrazolines16and19was not possible, but could be achieved by starting from azoxide/pyrazolines21with subsequent reduction of the azoxy group (23→9,24→25). Similarly, azo/oxiranes48and55were prepared by oxygenation of unsaturated azoxides (e.g.20) and chemoselective deoxygenation of the azo group by irradiation in methanol (49→48,54→55).
Cyclopropyl Building Blocks for Organic Synthesis, 36. Unprecedented Addition of Dialkoxycarbenes to Tetrasubstituted Alkenes: Bicyclopropylidene and 2‐Chlorocyclopropylideneacetate
Authors: de Meijere Armin , Kozhushkov Sergei I. , Yufit Dmitry S. , Boese Roland , Haumann Thomas , Pole David L. , Sharma Pradeep K. , Warkentin John
Published: June 2010

The cycloaddition reactions of several dialkoxycarbenes generated in situ from the corresponding 2,2‐dialkoxy‐Δ3‐1,3,4‐oxadiazolines of the type3with bicyclopropylidene1afford the dialkyl acetals of dispiro[2.0.2.1]heptane‐7‐one (4), whereas the analogous addition to methyl (1‐chloromethylene‐1‐carboxylate)cyclopropane26leads to the formation of a complex mixture of products. Those products can best be rationalized in terms of nucleophilic attack of the dialkoxycarbene on the strained CC double bond, to form a dipolar intermediate capable of a variety of intramolecular rearrangements. Several chemical transformations of the compounds of type4are reported.
O‐Glycoside Synthesis under Neutral Conditions in Concentrated Solutions of LiClO4 in Organic Solvents Employing O‐Acyl‐Protected Glycosyl Donors
Authors: Böhm Gerd , Waldmann Herbert
Published: June 2010

O‐Glycosides of pivaloyl‐protected glucose can be synthesized under neutral conditions in moderate yields by employing the pivaloylated β‐glucosyl fluoride 2d and the respective β‐benzyl phosphate 2e as glycosyl donors and 1 M solutions of LiClO4 in CH2Cl2 or CHCl3 as reaction media. The acetyl‐protected α‐ or β‐configured glucosyl trichloroacetimidates 1a and 1b were converted into the orthoesters 6 which were isolated in moderate to high yields. Under these conditions, acetyl‐protected glycosyl phosphates, acetyl‐ or pivaloyl‐protected glycosyl bromides and O‐pivaloylated glycosyl trichloroacetimidates were not converted to the desired O‐glycosides.
Selective Oxyfunctionalization of (Tricarbonylcyclohexadiene)iron‐Substituted Furans with Singlet Oxygen and Dimethyldioxirane
Authors: Adam Waldemar , Schuhmann Rosemarie M.
Published: June 2010

The versatility of the tricarbonyliron fragment as protecting group in the oxyfunctionalization of cyclohexadienyl‐substituted furans with singlet oxygen (1O2), dimethyldioxirane (DMD) and m‐chloroperoxybenzoic acid (mCPBA) was investigated. The photooxygenation of the (tricarbonylcyclohexadiene)iron‐substituted furans 1a and 1b in methanol gave, after reduction with triphenylphosphane, the furanone 2a and the enediones 3b as mixture of Z and E isomers in good yields. Precursors to these oxyfunctionalized products were the corresponding furan endoperoxides, which were trapped by methanol. The enedione Z‐3b was also obtained in the dimethyldioxirane oxidation, which was performed in boiling acetone to minimize the oxidative destructin of the tricarbonyliron moiety. In contrast, mCPBA was unsuitable for the oxyfunctionalization of the ligand sphere of such tricarbonyliron complexes due to the liberation of the organic ligand. While the decomplexation of the furanone 2a with cerium (IV) ammoniumnitrate (CAN) led selectively to the functionalized cyclohexadiene 4a, photooxygenation of the free furan 6a resulted in a complex mixture of oxidized compounds. Thus, protection of the 1,3‐cyclohexadiene moiety by tricarbonyliron complexation, oxidation (1O2, DMD) and decomplexation (CAN) offers a convenient and useful sequence for the regioselective oxyfunctionalization of such complex furans.
Glycosyl Imidates, 74. Synthesis of Ganglioside GM1 via a GM3 Intermediate
Authors: Greilich Ulrike , Brescello Roberto , Jung Karl‐Heinz , Schmidt Richard R.
Published: June 2010

The synthesis of GM1 (1) via GM3 intermediate 7 was based on lactose building‐block 5, sialyl donors 6, and a Galß(1–3)‐GalN3 donor 13α. Reaction of donor 13α with acceptor 7 in the presence of TMSOTf as catalyst afforded GM1 pentasaccharide 30. Azido group reduction, N‐acetylation, hydrogenolytic O‐debenzylation, and O‐acetylation furnished O‐acyl‐protected GM1 pentasaccharide 34. Chemoselective 1a‐O‐deacetylation and generation of O‐(pentaosyl)trichloro‐acetimidate 36 provided the required glycosyl donor for the application to azidosphingosine glycosylation procedure affording GM1 (1).
Highly Photostable Organic Fluorescent Pigments – A Simple Synthesis of N‐Arylpyrrolopyrrolediones (DPP)
Authors: Langhals Heinz , Grundei Thomas , Potrawa Thomas , Polborn Kurt
Published: June 2010

N‐Arylpyrrolopyrrolediones 1b‐g are prepared by the condensation of the corresponding lactones 2 and 5 with arylamines in the presence of dicyclohexylcarbodiimide. Bright red dye pigments are obtained with an intense red to orange solid‐state fluorescence.
Analogues of Cytostatic, Fused Indazolinones: Synthesis, Conformational Analysis and Cytostatic Activity Against HeLa Cells of Some 1‐Substituted Indazolols, 2‐Substituted Indazolinones, and Related Compounds
Authors: Arán Vicente J. , Flores María , Muñoz Pilar , Páez Juan A. , Sánchez‐Verdú Prado , Stud Manfred
Published: June 2010

A number of indazol‐3‐ol and indazolin‐3‐one derivatives were designed as open‐chain analogues of some previously studied cytostatic tetranuclear indazolinones. The former were prepared by starting with alkylation of the parent indazolinones (11 or its 5‐H analogue). Special mention deserves the method we developed for the direct alkylation of position 2 of indazolinone 11 with benzyl or picolyl halides. The prepared compounds were evaluated as cytostatic agents against HeLa cells, but only 1‐benzylindazolol 5a and 1‐(2‐fluorobenzyl)‐3‐methoxy‐ and 1‐benzyl‐3‐methoxyindazoles 14h, i display significant activity. Additional 13C‐NMR studies and conformational analysis using molecular mechanics and quantum‐mechanical semiempirical techniques confirm that the compounds designed as analogues of the model cytostatic indazolinones are not able to mimic effectively the structural features of the latter.
Electron Transfer Initiated Free Radical Additions of Perfluoroalkyl Iodides and Diiodides to Alkenes
Authors: Metzger JüRgen O. , Mahler Ralf , Schmidt Andreas
Published: June 2010

Perfluoroalkyl iodides were added in very good yields to 1,2‐dialkyl substituted double bonds of e.g. petroselinic acid initiated by lead/copper(II) acetate in methanol and by copper without solvent, respectively. Using the new initiator system lead/copper(II) acetate, we also obtained good yields in the additions of perfluoroalkyl iodides to allyl alcohol and ω‐unsaturated alcohols and of perfluoroalkyl 1,ω‐diiodides to methyl 10‐undecenoate.
[2 + 2] Photocycloaddition of Two Captodative Alkenes to 3‐Acetylthianaphthene
Authors: Döpp Dietrich , Hassan Alaa A. , Henkel Gerald
Published: June 2010

Photoexcited 3‐acetylbenzo[b]thiophene (1c) adds 2‐morpholinopropenenitrile (2a) in a [2 + 2] mode at the C2C3 bond regioselectively but stereounselectively with formation of cyclobuta[b][1]benzothiophenes 3a and 4a. In addition, the isomeric adduct 5 is formed from 2a and excited 2‐acetylbenzo[b]thiophene (1b) accompanying 1c as an impurity. Similarly, 2‐(tert‐butylthio)propenenitrile (2b) undergoes a smooth and highly regioselective but stereounselective [2 + 2] photoaddition to 1c yielding a mixture of two isomeric adducts from which compound 3b may be separated by recrystallization. The configuration of 5 was unambiguously confirmed by an X‐ray crystal structure analysis. The structures of the other cycloadducts were derived by a comparison of their 1H‐NMR spectral data with those of closely related substances from other work.
Facile Synthesis of Polycyclic pyridines, Bipyridines, and Oligopyridines
Authors: Keuper Ralf , Risch Nikolaus
Published: June 2010

The preparation of polycyclic heterocycles with one or more nitrogen atoms and different binding angles by a domino reaction is described. These compounds (4–6, 8a–b) are formed by the reaction of β‐amino ketone hydrochlorides 1 or 2 (Mannich bases) with ketones 3. Especially the synthesis of the terpyridines 8a and 8b in a double domino reaction is very useful (yield 70 and 59%) and opens a route to torands.
Microwave‐Assisted Diels‐Alder Reaction Supported on Graphite
Authors: Garrigues Bernard , Laporte Christian , Laurent Régis , Laporterie André , Dubac Jacques
Published: June 2010

The coupling of graphite (as a support) with microwaves (as an energy source), a new type of “dry reaction”, was studied for some Diels‐Alder reactions involving anthracene and azadienes. Graphite is responsible for a high‐temperature gradient leading to increased reaction rates as compared to conventional procedures using a solvent.
Dimerizations of 2‐Alkylbenzotriazoles and Chemical Evidence of Radical Intermediates from X‐ray Studies
Authors: Katritzky Alan R. , Jesorka Aldo , Wang Jin , Yang Baozhen , Wu Jing , Steel Peter J.
Published: June 2010

Treatment of 2‐alkylbenzotriazoles with lithium diisopropylamide (LDA) at −78°C gave, depending on workup conditions, either dimers of the type Bt2CHRCHRBt2 (2) (Bt2 = benzotriazol‐2‐yl), or mixtures of symmetrical Z and E olefins (3) (RCHCHR), in high yields via radical intermediates. The racemic and meso isomers of 2, which differ substantially in properties such as melting points, 1H and 13C NMR, were isolated and characterized (three by X‐ray crystallography). Both the meso and racemic dimers of 2 were reduced by Na to give mixtures of Z and E olefins in high yields with the elimination of the benzotriazole anion. 2‐Alkylbenzotriazoles (1) were also converted by Na into the corresponding alkanes and benzotriazole. The intermediates were trapped by benzophenone to give, depending on the reaction procedure (see Scheme 2), adducts 6 or adducts 6 with dimers 2, benzotriazol‐2‐ylalkene 7 and compound 8 (R  H), compound 9 (R  CH3). Several compounds with dibenzotriazol‐2‐yl groups or benzotriazol‐1‐yl and benzotriazol‐2‐yl groups in the same molecule were synthesized and further investigated via lithiation followed by the addition of benzophenone or benzaldehyde. This further indicated that the radical reaction is faster than the nucleophilic reaction.
A Transannularly Bridged Bis(calix[4]arene) Forming a Multiple Ansa Compound
Authors: Siepen Astrid , Zett Andreas , Vögtle Fritz
Published: June 2010

The reaction of the chloromethylated calix[4]arene 1 fixed in the “cone” conformation with 4,4′‐dihydroxybiphenyl 2 leads to 4, which is the first example of a bis(calix[4]arene) macrocycle threaded by two intramolecular bridges. It thus contains three cavities in one multiple ansa molecule.
Photoresponsive Carboxylic Acids
Authors: Herges Rainer , Reif Wolfgang
Published: June 2010

A norbornadiene tetracarboxylic acid was synthesized the pKs of which can be changed by irradiation forming the quadricyclane derivative or by catalytical reisomerization to the norbornadiene. The pKs difference of both isomers in the second and fourth dissociation step is 0.59 and 0.68 units. Photochemical isomerization proceeds without decomposition at high pH (≥ 9.0). Reisomerization of the quadricyclane to the norbornadiene with a RhI complex is also a clean reaction, but rather slow with t1/2 = 5 d at room temperature. We attribute the pH change of an aqueous solution during isomerization to the formation or cleavage of intramolecular hydrogen bonds between the adjacent carboxyl groups and accumulation or dispersion of negative charge in the quadricyclane and norbornadiene, respectively.
A Facile Synthesis of Dinitro[2.2]metacyclophane and Its Partial Reduction
Authors: Tsuge Akihiko , Moriguchi Tetsuji , Mataka Shuntaro , Tashiro Masashi
Published: June 2010

Both aromatic rings in [2.2]metacyclophanes(MCPs) can be easily nitrated in good yields by using the HNO3/dichloromethane system under mild conditions. This facile method is clearly superior to the nitration by strong nitrating agents such as nitronium tetrafluoroborate. Partial reduction of dinitro[2.2]MCP (2a) affords the intriguing aminonitro[2.2]MCP (3) which is one of the ultimate models of intramolecular charge‐transfer interaction. Compound 3 shows a significant bathochromic shift due to through‐space interaction between two aromatic rings.
[4 + 2] Cycloaddition Reactions of a 4a,8a‐Methanophthalazine with Electron‐Rich Alkynes: A New Synthesis of Substituted 1,6‐Methano[10]annulenes
Authors: Laue Jörg , Seitz Gunther
Published: June 2010

The novel propellane3containing an electron‐rich cyclohexadiene and an electron‐deficient diazadiene system in one and the same molecule reacts site selectively with the electron‐rich alkynes4and8as well as with cyclooctyne (10) to yield the interestingly substituted novel 1,6‐methano[10]annulenes7,9, and11. In contrast to this course of reaction, benzyne (12) undergoes a cycloaddition with the cyclohexadiene moiety of3with high site selectivityantito the methano bridge to furnish the pentacyclic pyridazine derivative14. Interestingly benzyne (12) is able to react with the diazadiene system of the phthalazine17to form the triptycene19via the azo compound18.
Unexpected Pyrazole → 1,2,4‐Triazole Ring Transformation
Authors: Moderhack Dietrich
Published: June 2010

The pyrazolyl‐substituted amidrazones 3 were found to undergo slow conversion into the 1,2,4‐triazolyl ketone hydrazones 8 when kept in ethanolic solution at 20°C. The crucial step in this transformation is apparently air oxidation of 3 to the intermediate 4, since employment of an additional oxidant greatly enhanced the rate.
Tuberosides A, B, and C, Novel Triterpenoid Saponins from the Hypoglucaemic Fraction of Ullucus tuberosus
Authors: Espada Alfonso , Jiménez Carlos , Dopeso Jose , Riguera Ricardo
Published: June 2010

Three novel triterpenoid saponins, tuberoside A (1), B (2), and C (3), were isolated as sodium and choline salts from the methanolic extract of the tubers of Ullucus tuberosus Caldas (Syn.: U. kunthii H.B.K.), which shows hypoglucaemic activity. Their structures were established on the basis of 2D‐NMR and FAB‐MS experiments and were confirmed by chemical methods. This is the first chemical study of a plant of the genus Ullucus.
Reactions with Twofold Bridged Sulfone‐Substituted Dewar Benzenes – Preparation of New Dewar Benzene Derivatives
Authors: Ohlbach Frank , Gleiter Rolf , Oeser Thomas , Irngartinger Hermann
Published: June 2010

The twofold bridged sulfone‐substituted Dewar benzenes 15,16‐bis(tert‐butylsulfonyl)tetracyclo[7.5.2.01,9.02,8]hexadeca‐2(8),15‐diene (7a), 17,18‐bis(tert‐butylsulfonyl)tetracyclo[8.6.2.01,10.02,9]octadeca‐2(9),17‐diene (7b), 2,3‐bis(tert‐butylsulfonyl)‐1,4,5,6‐tetramethylbicyclo[2.2.0]hexa‐2,5‐diene (11), and 15‐(phenylsulfonyl)‐16‐(trimethylsilyl)tetracyclo[7.5.2.01,9.02,8]hexadeca‐2(8),15‐diene (13a) were treated with SmI2, methyllithium, phenyllithium, and methyl, phenyl, and benzyl Grignard reagents, respectively. In the case of the reduction with SmI2 one tert‐butylsulfonyl substituent (7a, 7b, 11) and the phenylsulfonyl group in 13a could be removed. Compound 7a reacts with methyllithium and phenyllithium with replacement of one RSO2 substituent by the alkyl or aryl group, respectively. With methyl and benzylmagnesium bromide both RSO2 groups in 7a could be replaced. The reaction of 7a with phenylmagnesium bromide leads to the mono‐ and disubstituted products and in addition to dimers of substituted phenyl Dewar benzenes. For the reaction with organolithium and Grignard compounds there are indications of a SET mechanism. The X‐ray structures of 15,16‐dimethyltetracyclo[7.5.2.01,9.02,8]hexadeca‐2(8),15‐diene (32a) and the corresponding dibenzyl derivative 834a) were investigated by using single crystals.
Synthesis of rac‐Presilphiperfolan‐9‐ol
Authors: Weyerstahl Peter , Marschall Helga , Schulze Matthias , Schwope Ina
Published: June 2010

rac‐Presilphiperfolan‐9‐ol (2) and three of its epimers (24, 29, 30) were synthesized by starting from the known 8‐hydroxy‐3,3,5‐trimethylbicyclo[3.3.0]octan‐2‐one (10). The spectroscopic data of rac‐2 are identical with those of the natural (‐)‐presilphiperfolan‐9‐ol, previously isolated from Artemisia laciniata. rac‐2 has a strong woody, amber odor whereas the 9‐epimer 24 smells strongly patchouli‐like.
Structure‐Odor Correlation, XXIV. Synthesis and Olfactory Properties of Damascone and Damascenone Analogs
Authors: Weyerstahl Peter , Licha Kai
Published: June 2010

The aldehydes rac‐1, rac‐2, and 3 were conveniently prepared by starting from isophorone (4). Reaction of 1–3 with (E,Z)‐1‐bromo‐1‐propene (14) afforded the rac‐allylic alcohols (E,Z)‐15, ‐18, and ‐20. The alcohols were oxidized to the damascone/damascenone analogs 1‐(3,5,5‐trimethyl‐2‐cyclohexen‐1‐yl)‐ (rac‐16), 1‐(3,5,5‐trimethyl‐1‐cyclohexen‐1‐yl)‐ (rac‐19), and 1‐(3,5,5‐trimethyl‐1,3‐cyclohexadien‐1‐yl)‐2‐buten‐1‐one (21), and the (E/Z) isomers were separated by FC. Their olfactory evaluation shows that the highly estimated odor of damascone (A, B) and damascenone (C) is more or less lost. This result can be explained by force‐field calculation of the lowest energy conformation of 16, 19, and 21 in comparison with those of A–C.
Thermal Isomerisations, XXIV. Gas Phase Kinetics of the Pyrolysis of Some 3,3‐Dimethyl‐1‐alkyl‐cyclopropenes: Some Surprising Substituent Activation Effects and the Intramolecular Trapping of Vinylidene Intermediates
Authors: Hopf Henning , Plagens Andreas , Walsh Robin
Published: June 2010

The gas phase pyrolyses of four 3,3‐dimethyl‐1‐alkylcyclopropenes were studied for which the 1‐alkyl substituents are ethyl‐ (6), isopropyl‐ (7), 1′‐butyl‐ (8) and 1′‐isoamyl‐ (9). Rate data over a 50°C temperature range were obtained and Arrhenius parameters are reported both for overall reactions and individual pathways for all compounds. Tests confirm all reactions to be unimolecular and homogeneous. For 8 and 9, noteworthy products are cyclopentenes, whose presence demonstrates the involvement of vinylidene intermediates. The substantial product yields of 2,4‐alkadienes together with dramatic rate enhancement effects of these 1‐alkyl substituents (relative to 1‐methyl) are explained by the involvement of vinylcarbene intermediates in this pathway. Minor, transient products from 6, 8 and 9 are probably isomeric cyclopropenes. This suggests further pathways for vinylidene intermediates, whose reactivity pattern is briefly reviewed.
Biologically Active Glycosides from Asteroidea, 35. Isolation and Structure of Four New Steroid Glycoside Di‐O‐sulfates from the Starfish Asteropecten latespinosus
Authors: Higuchi Ryuichi , Fujita Masanori , Matsumoto Shuji , Yamada Koji , Miyamoto Tomofumi , Sasaki Takuma
Published: June 2010

Four new steroid di‐O‐sulfates, latespinoside A (1), B (2), C (3), and D (4), were isolated from the crude glycoside fraction of the chloroform/methanol extract of the starfish Asteropecten latespinosus as minor components. Their structures were determined on the basis of spectral data as disodium salts of (20S)‐20‐hydroxy‐6α‐(4‐O‐sulfo‐β‐D‐quinovopyranosyloxy)‐3β‐sulfooxy‐5α‐cholesta‐9(11),24‐diene (1), (20S)‐20‐hydroxy‐6α‐(4‐O‐sulfo‐β‐D‐quinovopyranosyloxy)‐3β‐sulfooxy‐5α‐cholest‐9(11)‐ene (2), 6α‐(4‐O‐sulfo‐β‐D‐quinovopyranosyloxy)‐3β‐sulfooxy‐5α‐cholesta‐9(11),17(20)Z,24‐trien‐23‐one (3), and 6α‐(4‐O‐sulfo‐β‐D‐quinovopyranosyloxy)‐3β‐sulfooxy‐5α‐androst‐9(11)‐en‐17‐one (4). Compound 4 is, to the authors' knowledge, the first androstane derivative isolated from starfish. In addition, compounds 3 and 4 show weakly cytotoxic activity against murine lymphoma L1210 cells in vitro.
Cycloadditionen von 6H‐1,3,4‐Oxadiazin‐6‐onen (4,5‐Diaza‐α‐pyronen), 15.Reaktionen von 6H‐1,3,4‐Oxadiazin‐6‐onen mit Norbornadien. Ein neuer Weg zu 3,6‐disubstituierten α‐Pyronen
Authors: Christl Manfred , Bodenschatz Gabriele , Feineis Erich , Hegmann Joachim , Hüttner Gerhard , Mertelmeyer Stefan , Schätzlein Klaus
Published: June 2010

Cycloadditions of 6H‐1,2,4‐Oxadiazin‐6‐ones (4,5‐Diaza‐α‐pyrones), 15.

Part 14: Ref.[1].

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Reactions of 6H‐1,3,4‐Oxadiazin‐6‐ones with Norbornadiene. A New Route to 3,6‐Disubstituted α‐Pyrones

Upon reaction with norbornadiene, ten disubstituted 1,3,4‐oxadiazin‐6‐ones 1 were converted into 3,6‐disubstituted α‐pyrones 6. For this purpose, solutions of the substrates were treated with boron trifluoride‐ether or trifluoroacetic acid. The smooth formation of 6 was also observed when a γ‐oxo ketene, initially generated by heating a solution of the substrates in the absence of boron trifluoride–ether, was allowed to react with the Lewis acid. Without use of an acid, only 6f could be obtained free from further compounds, whereas in the other cases enol lactones and 1:2 products of the types 8 and 7 were formed additionally. Oxadiazinone 1j gave enol lactone 10 in the noncatalysed reaction.
Triazolo[4,5‐b]‐ and Imidazo[4,5‐b]pyridines as Substrates of NAD Glycohydrolase: Evidence for Two Competitive Transglycosylatin Reaction Sites
Authors: Tono‐Oka Shuichi , Azuma Ichiro
Published: June 2010

The NAD+ glycohydrolase‐catalysed transglycosidation reaction of pyrido‐annulated triazole 1 and imidazole 2 was investigated. In both cases two regioisomers, N1‐ribosylated (3 and 5) and N3‐ribosylated products (4 and 6), were efficiently obtained in roughly equal ratio. The regioisomers were distinguished from each other on the basis of 15N‐NMR data. The present study furnished evidence of two competitive sites of transglycosidation in the triazole 1 and the imidazole 2. The occurrence of competition is probably attributable to a tautomeric equilibrium between 1a and 1b (2a and 2b).
New Types of Nonionic Surfactants with Sugar Head Groups
Authors: Schmidt Richard R. , Jankowski Karin
Published: June 2010

The head group/lipophilic tail ratio is used to categorize amphiphilic compounds into different types. Some representatives of the 2/1 type with two sugar head groups and one lipophilic chain, namely compounds 6a–d, were synthesized from readily available precursors. Similarly, from 2,3‐di‐O‐alkyl and 1,3‐di‐O‐alkyl derivatives of D‐threitol 2/2‐type amphiphiles 13a–d, 15a–d and 20a–d, respectively, were obtained. Due to the different spatial demand of the sugar moieties relative to the lipophilic part, surface tension (σ) and critical micelle concentration (cmc) are clearly distinguished in these different structural types of nonionic surfactants.
3H‐Azepines by Intramolecular Condensation Reaction of 1,6‐Diamino‐1,3,5‐hexatrienes
Authors: Kowalski Dorothee , Erker Gerhard , Kotila Sirpa
Published: June 2010

2,7‐Disubstituted 3H‐azepines (2a–d) are obtained by acidcatalyzed thermolytic deamination of 1,6‐disubstituted 1,6‐diamino‐1,3,5‐hexatrienes 1a–d in moderate yields. The reaction probably involves reversible conjugated enamine ⇌ imine tautomerization indicated by the formation of the respective five‐membered ring competition products 3. Compounds 2a and 3b were characterized by X‐ray diffraction.
The Use of Vicinal Twofold Heck Reaction Products in Diastereoselective Sequential Michael Additions — A Convenient Access to Enantiomerically Pure Six‐Ring Anellated Cispentacin Derivatives
Authors: Voigt Katharina , Lansky Annegret , de Meijere Armin , Noltemeyer Mathias
Published: June 2010

The palladium‐catalyzed coupling reactions of various acrylic acid derivatives 2a–e (e.g. methyl, tert‐butyl, benzyl, menthyl esters) with 1,2‐dibromobenzene (1), 1,2,3‐tribromobenzene (4) and 1,2‐dibromocyclohexene (6) yielded the correspondingly substituted ortho‐diethenylarenes 3a–e, 1,2,3‐triethenylarenes 5a,b and (E,E)‐1,3,5‐hexatriene derivatives 7a,b. Some of these vicinal diacrylates (3a–d, 5b, 7a,b) were converted to 1,2,3‐trisubstituted indane‐ and tetrahydroindane derivatives 10a–d, 15a,b, 18, 20, 23, and 12a,b, 16b by domino conjugate addition of nitrogen, carbon, and sulfur nucleophiles. With benzyl(trimethylsilyl)amine (9) as an ammonia equivalent, the relative configuration of all three newly formed stereogenic centers was controlled (d.e. >90%). Therefore, with chiral non‐racemic ammonia equivalents like benzyl[(S)‐phenylethyl]amine (14) and TMS‐(R)‐AMP (17), protected diastereomerically pure β‐amino esters were obtained, which could easily be deprotected by standard methods to yield the enantiomerically pure β‐amino acids 27 and 28.
Porphyrin Blocking Groups in Amide‐Based Rotaxanes
Authors: Vögtle Fritz , Ahuis Friedrich , Baumann Sven , Sessler Jonathan L.
Published: June 2010

The synthesis of amide‐based symmetrical rotaxanes2a,bbearing porphyrin blocking groups is firstly described. These compounds can be obtained by a one‐step one‐pot reaction only if the macromonocyclic host template complementary to the threading guest is found. The symmetry of the axle is removed by introducing an unsymmetrical central part, leading to the formation of rotaxane2c. Different blocking groups were used to obtain the non‐symmetrical rotaxane3a. The bis‐Zn2+complex10aof the rotaxane2awas isolated. A nonionic supramolecular complex7was assumed as threaded intermediate, which was blocked by reaction with the stopper components. The amide‐type rotaxane system thus proved to be variable with respect to all its parts including stopper components of different reactivity, bulkiness and supramolecular functionality.
Transesterification of Phosphodiester by a Zinc‐Containing Cyclen Derivative: Identification of the Active Species
Authors: Kalesse Markus , Loos Andrea
Published: June 2010

The active site analogue 2 of alkaline phosphatase was synthesized and its hydrolytic activity was tested. Efficient hydrolysis was observed at pH > 8 at various concentrations of the hydrolytic species. The cyclic phosphate 3 derived from transesterification could be identified by 31P‐NMR spectroscopy. A comparison of the hydrolysis results with the species distribution curve revealed the ZnLOH species as the active complex. The complex stability constant (log KZnL) of ligand 7 was determined to be 13.7 (± 0.5). K′ for the hydrolysis of the p‐nitrophenyl phosphate ester of propylene glycol (1) with 2 (0.02 M, pH = 8.35) is 1.5 × 10−3 s−1 at 50°C.
Identification and Synthesis of Elymniafuran, a New Monoterpene from the Butterfly Elymnias thryallis
Authors: Schulz Stefan , Steffensky Mirjam , Roisin Yves
Published: June 2010

The main constituent of the scent gland secretion of the tropical butterfly Elymnias thryallis (Lepidoptera: Satyridae) could be identified as (S)‐2‐methyl‐1‐(4‐methyl‐2‐furyl)‐3‐buten‐2‐ol (elymniafuran, 3). It is accompanied by small amounts of (E)‐ and (Z)‐4‐methyl‐(2‐methyl‐1,3‐butadienyl)‐furan (4) as well as the spiro acetal 3,9‐dimethyl‐1,6‐dioxaspiro[4.5]dec‐3‐ene (10). The structural assignment of these new natural products as well as the synthesis and enantiomeric separation by chiral gas chromatography are described.
Determination of the Rotational Energy Barrier of Planar‐Chiral Cyclophanes Using Dynamic Enantioselective Gas Chromatography and Computer Simulation
Authors: Hochmuth Detlev H. , König Wilfried A.
Published: June 2010

We synthesized numerous new monosubstituted dioxa[11]‐paracyclophanes, which are planar‐chiral atropisomers due to the hindered rotation of the bridge about the aromatic plane, and we were able to resolve the enantiomers of these compounds by enantioselective gas chromatography with selectively modified cyclodextrins as chiral stationary phases in polysiloxane solution. As a consequence of the competition between enantiomeric resolution and enantiomerization (interconversion) during the gas chromatographic process, coalescence phenomena or formation of plateaus between the peaks of both enantiomers are observable. The combination of these dynamic gas chromatographic investigations with computer simulation of elution profiles allows the facile and precise determination of the energy barrier of the enantiomerization reaction and the elucidation of the influence of substituents on the energy barrier.
An Unusual C‐1C‐2 Ring‐Splitting of Pyranosides by a Retro‐Aldol Reaction — a Route to New Chiral Building Blocks
Authors: Peseke Klaus , Aldinger Stephan , Reinke Helmut
Published: June 2010

The treatment of the α‐oxoketene dithioacetal sugar derivatives 2 and 7 with concentrated hydrochloric acid in THF leads to the open‐chain uloses 3 and 8. The reaction mechanism can be rationalized as a retro‐aldol reaction. This rationalization was supported by reacting 2 and 7 with DCl/D2O. Compound 3 was converted into the chiral pyrazoles 12 and 13. The branched‐chain ulose 2 forms the thiopyranosidulose 15 when treated with diluted aqueous sulfuric acid in THF. The mechanism of this reaction was investigated by 13C‐labelling of the starting compound 2.
Functionalized Derivatives of Benzocrown Ethers, I. Ionophores Containing Amino and Pyridinium Groups Derived From Benzo‐15‐crown‐5, Benzo‐18‐crown‐6, and Dibenzo‐18‐crown‐6
Authors: Barboiu Mihai , Popescu Georgeta , Barboiu Camelia , Supuran Claudiu T. , Luca Constantin
Published: June 2010

Acylation reactions of benzocrown ethers with N‐phthalimido‐protected derivatives of β‐alanine and 11‐aminoundecanoic acid, respectively, were investigated in acid catalysis by using the Eaton reagent. Deprotection of the obtained compounds by hydrazinolysis afforded derivatives with free amino groups the reaction of which with one or two equivalents of 2,4,6‐trisubstituted pyrylium salts furnished pyridinium derivatives. All these new benzocrown ether derivatives were characterized by elemental analysis and IR and NMR spectroscopy.
Synthesis of the First Chiral Bisindolyl Monomethinium Cyanine Dyes
Authors: Eggers Lutz , Buß Volker
Published: June 2010

The synthesis of the chiral monomethine cyanine dyes 8 and 9 starting with the achiral indole 1 is described. Key intermediates are the new chiral Fischer bases R‐ and S‐4, which were separated after diastereomeric salt formation. The conformation of the dyes 8 and 9 is twisted di‐Z, according to NOE and dynamic NMR spectroscopy. The free energy difference between oppositely twisted conformations is ca. 2.5 kJ mol−1.
Syntheses and Structures of 2,6‐Substituted Barbaralanes
Authors: Quast Helmut , Becker Christian , Witzel Martina , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: June 2010

Several 2,6‐substituted barbaralanes, viz. 1d–g, have been synthesised from Meerwein's diketone (2). Treatment of dinitrile 3 with hydrochloric acid in boiling methanol followed by hydrolysis of the intermediate Pinner salt yields the dimethyl dicarboxylate 4 which is brominated to afford the exo,exo dibromo diester 5. Reductive cyclisation of 5 gives rise to the formation of dimethyl 2,6‐barbaralanedicarboxylate (1d). – Addition of (phenylethynyl)cerium(III) chloride to 2 followed by acid‐induced dehydration of the resulting endo,endo diol 6 yields the bis(phenylethynyl)diene 7, which is cyclised to the bis(phynylethynyl)barbaralane 1e by allylic bromination and subsequent treatment of the exo,exo dibromide 8 with the zinc‐copper couple. Likewise, the exo,exo dibromo disulphone 11, which is obtained from 2 via the bis(vinyl sulphide) 9 and the bis(vinyl sulphone) 10, is converted into the bis(phenylsulphonyl)barbaralane 1f. – Trifluoromethylation of diketone 2 with trimethyl(trifluoromethyl)silane in the presence of a source of fluoride ions affords a mixture of the O silylated endo,endo diol 12 and the oxatwistane 13. Hydrochloric acid converts the latter into the hydroxy ketone 16, which yields 12 on treatment with trimethyl(trifluoromethyl)silane and tetrabutylammonium fluoride. Desilylation of 12 to furnish the endo,endo diol 14 requires prolonged treatment with hydrofluoric acid under phase‐transfer catalysis. Vigorous conditions are also necessary for the dehydration of 14 with phosphorus oxychloride in pyridine to afford the bis(trifluoromethyl)diene 15. Cyclisation of 15 to the bis(trifluoromethyl)barbaralane 1g is performed in the usual way by allylic bromination and subsequent reduction of the dibromide 17 with the zinc‐copper couple. – The configurations and conformations in the crystals have been elucidated by X‐ray diffraction analyses for the bicyclo[3.3.1]nonane derivatives 5, 8, and 11 as well as the barbaralanes 1f and h. In the solid state, 1f appears to exist as a single non‐rearranging valence tautomer. The atomic distances found for 1h indicate the presence of equilibrating non‐equivalent valence tautomers. The results are compared to those from X‐ray diffraction analyses of other degenerate barbaralanes and heterobarbaralanes.
Reaction of 4′‐Benzyloxy‐2‐(4‐pyridinyl)acetophenone with Ethylmagnesium Chloride: UnusualC‐Benzylation and in situ Reduction by β‐Hydrogen Transfer
Authors: Haroutounian Serkos A. , Couladouros Elias A.
Published: June 2010

In solution, 4′‐benzyloxy‐2‐(4‐pyridinyl)acetophenone (1) mainly exists as enol4which does not undergo typical Grignard addition reactions. Treatment with an excess of ethylmagnesium chloride, however, initiates an unusual sequence of transformations leading to formation of theC‐benzylated compounds2and3.
Rearrangement of a Bicyclo[3.2.0]hept‐2‐ene to a Bicyclo[4.1.0]hept‐4‐ene
Authors: Behrendt Uwe , Gabor Barbara , Mynott Richard , Butenschön Holger
Published: June 2010

The chemistry of the highly substituted cyclobutanone derivative 2, which is easily accessible from 1, is dominated by the steric hindrance caused by the substitutents: Reduction with hydride reagents and nucleophilic additions with methyllithium are less stereoselective than corresponding reactions with less substituted bicyclo[3.2.0]hept‐2‐en‐6‐one derivatives, but under certain conditions, the exo product predominates, with methyl‐, benzyl‐, ethenyl‐, and ethynylmagnesium halides no nucleophilic addition at the carbonyl group is observed, presumably as a result of the steric hindrance. Instead, an unexpected rearrangement to the bicyclo[4.1.0]heptane carbon skeleton occurs with complete diastereoselectivity and high yields. The rearrangement is rationalized by an increase of the carbocationic character of the carbonyl carbon atom as a result of a coordination of the carbonyl oxygen atom at the Lewis acidic magnesium. This facilitates rearrangement of a cyclobutyl carbenium ion to a cyclopropylmethyl carbenium ion, the latter being stabilized by the amino group. Remarkably, with Grignard reagents derived from propargyl or allyl halides, no rearrangement is observed. The constitutions and configurations of the products were determined by 1H‐ and 13C‐NMR spectroscopy using techniques including NOESY and 2D‐INADEQUATE.
Fluoroselenenylation of Acetylenes with Xenon Difluoride–Diorganyl Diselenides; Synthesis and Structure Elucidation of Functionalized Vicinal (E)‐Fluoro(organylseleno)olefins
Authors: Poleschner Helmut , Heydenreich Matthias , Schilde Uwe
Published: June 2010

We carried out the fluoroselenenylation of hex‐3‐yne with xenon difluoride and functionalized diselenides (dimethyl acetal‐ and carboxylic acid ester‐substituted) to the corresponding substituted vicinal (E)‐fluoro(organylseleno)olefins. Consecutive reactions afforded crystalline 2,4‐dinitrophenylhydrazone and carboxylic acid derivatives. Nonfunctionalized vicinal (E)‐fluoro(organylseleno)olefins were alkylated with trimethyloxonium tetrafluoroborate, triethyloxonium tetrafluoroborate, and methyl trifluoromethanesulfonate to the corresponding fluoroalkenyldiorganylselenonium salts which were characterized either as tetrafluoroborate or as tetraphenylborate salts. X‐ray analysis of [(E)‐4‐fluorooct‐4‐en‐5‐yl]dimethylselenonium picrate (11) proved unambiguously that the fluoroselenenylation of acetylenes with XeF2–R2Se2 and XeF2–PhSeSiR3 reagents proceeds via trans additions.