bluuebunny/crossref_metadata_2025 huggingface dataset:
cis/trans‐ozonides of cycloolefins
Authors: Griesbaum Karl , Ball Volker , Beck Johannes , McCullough Kevin
Published: July 2007

Ozonolyses in pentane of the unsubstituted cycloolefins having eleven‐, twelve‐, fourteen‐ and sixteen‐membered rings (1b‐e) and of cyclohexadecen‐8‐one (12) gave the corresponding cis‐ (2b‐e; cis‐15a) and trans‐ozonides (3b‐e; trans‐15a), whereas cyclodecene (1a) gave only the corresponding cis‐ozonide (2a). Ozonolyses on polyethylene of the dimethyl‐substituted cycloolefins bearing fourteen‐ and sixteen‐membered rings (7b, c) also afforded cis‐ and trans‐isomeric ozonides (8, 9), whereas from the twelve‐membered ring (7a) only the corresponding cis‐ozonide (8a) was formed.
Electrophilic reactions of the dibenzo[a,d]tropylium ion
Authors: Henninger Joachim , Mayr Herbert , Patz Matthias , Stanescu Michaela Dina
Published: July 2007

The kinetics of the hydride transfer reactions of the dibenzo‐tropylium ion (2) with dimethylphenylsilane (5) and triphenylsilane (6) were used to determine its electrophilicity parameter E = ‐0.71. The nucleophiles 7–9 react 10–40 times faster with 2 than expected from the linear free energy relationship (1), probably due to the formation of a ‐stabilized carbocation (e.g. 15). A detailed investigation of the reaction of 2 with isobutene (4) shows that the linear addition product 13a and the cyclization products are not formed via a common intermediate.
Unexpected reaction of 4‐(2,4,6‐triphenylpyridinio)phenolate with urea in aqueous solution — structure of 1‐(4‐hydroxyphenyl)‐2,4,6‐triphenylpyridinium cyanate
Authors: Milart Piotr , Mucha Dariusz , Stadnicka Katarzyna
Published: July 2007

During crystallization of the pyridinium N‐phenolate dye 1 from a saturated aqueous solution of urea, 1‐(4‐hydroxyphenyl)‐2,4,6‐triphenylpyridinium cyanate (4) is formed unexpectedly as verified by IR, 1H‐NMR and X‐ray structural analysis. Such a course of reaction can be explained by the strong nucleophilic character of the betaine dye 1. The anion of 4, [NCO]−, is disordered between two positions; one of them can be assigned to an isocyanate and the other to a cyanate group. The nitrogen atom of the anion is involved in an intermolecular, nearly linear hydrogen bond with the hydroxy group of the cation whereas its oxygen atom is pointing towards the pyridinium ring of an adjacent pyridinium cation.
3,4‐bis(O‐tert‐butyldimethylsilyl)‐6‐O‐tosyl‐D‐glucal: A probe for the mechanism of the iodine(III)‐promoted allylic oxidation of glycals
Authors: Kirschning Andreas
Published: July 2007

The reaction of 3,4‐bis(O‐tert‐butyldimethylsilyl)‐6‐O‐tosyl‐D‐glucal 4 with the Koser reagent [PhI(OH)OTs] unexpectedly afforded tetrahydrofurfural 6 as well as 2,3‐anhydropyranose 7 as major products. This unprecedented, stereoselective transformation helps to gain further insight into the mechanism of the well‐documented hypervalent iodine‐promoted allylic oxidation of cyclic enol ethers. A novel chemoenzymatic method for the preparation of glucal 4 in high yield is presented.
Glycolipids from sponges, III. Glycosyl ceramides from the marine sponge Agelas conifera
Authors: Costantino Valeria , Fattorusso Ernesto , Mangoni Alfonso
Published: July 2007

The glycosphingolipid (GSL) composition of the marine sponge Agelas conifera was investigated. In addition to three GSLs previous isolated from Agelas clathrodes (2a‐4a), the novel α‐glycosylceramide 1a was isolated as a major component of the GSL mixture, and its structure was elucidated by extensive NMR studies and by chemical analysis.
Derivatives of natural tetrapyrroles for photodynamic therapy, 3. Oxidative degradation studies on porphyrins with chromic acid
Authors: Gauler Rainer , Hesse Ulrike , Risch Nikolaus
Published: July 2007

Until now the composition of the complex porphyrin mixtures of hematoporphyrin derivative (HPD) and Photofrin II could not be clarified in detail. We investigated the applicability of oxidative degradation to the structural assignment of HPD constituents. Therefore, some fundamental work concerning the characterization of the relevant degradation products had to be done. In this article we present the spectral and analytical data of monomeric and dimeric maleimides potentially arising from the corresponding constituents of HPD.
Cycloaddition of Functionalized Nitrile Oxides and Fulminic Acid to [60]Fullerene
Authors: Irngartinger Hermann , Weber Anton , Escher Thomas
Published: July 2007

Cycloaddition of nitrile oxides to [60]fullerene led to [60]fullereno[1,2‐d]isoxazole derivatives 1b–d. [60]Fullereno[1,2‐d]isoxazole (1a) is the corresponding cycloadduct with fulminic acid. X‐ray structure analyses of compound 1b and 1e were determined.
Phenazin‐5(10H)‐yls, 4. 10‐Ethylphenazin‐5(10H)‐yl · H2O: Crystal Structure, Magnetic Susceptibility and Intermolecular π‐π Interactions (Pimerization)
Authors: Gleiter Marco R. , Krieger Claus , Neugebauer Franz A. , Kremer Reinhard K.
Published: July 2007

The unit cell of 10‐ethylphenazin‐5(10H)yl · H2O consists of eight phenazin‐5(10H)‐yls that are arranged in four independent radical pairsA–D. All pairs show close interplanar distances (3.28–3.36 Å). Furthermore,A, B, andDare characterized by short intermolecular contacts between atoms with significant spin populations. This is not valid for the pairCwith the closest interplanar distance of 3.28 Å. Magnetic susceptibility measurements as a function of temperature indicate complete spin pairing (“pimerization”) between 20 and 100 K. Therefore, the radical pairCprovides evidence that unspecific close interplanar contacts together with a reasonable overlap of the π systems are sufficient to lead to pimerization.
Ethynylation of Aryl Halides by a Modified Suzuki Reaction: Application to the Syntheses of Combretastatin A‐4, A‐5 and Lunularic Acid
Authors: Fürstner Alois , Nikolakis Katharina
Published: July 2007

On treatment with trimethyl borate sodium acetylide undergoes a palladium‐catalyzed cross coupling with functionalized aryl halides or triflates in reasonable to good yields. The ethynylarenes thus obtained serve as building blocks for the formation of the highly effective tubulin polymerization inhibitors combretastatin A‐4 (1) and A‐5 (2) as well as for the synthesis of the plant‐growth regulator lunularic acid (36).
Synthesis of the Isotopically Labelled C‐Terminal Fragment of Zervamicin: An Approach to the Synthesis of Aib‐Containing Peptides
Authors: Ogrel Alexei , Bloemhoff Wim , Lugtenburg Johan , Raap Jan
Published: July 2007

The isotopically labelled C‐terminal fragment of zervamicin, H‐Hyp10‐[4,4‐2H2‐Gln]‐Aib‐Hyp‐Aib‐Pro‐Phl16, has been synthesized in solution by a Fmoc/tert‐butyl strategy in 28% overall yield. The Fmoc group was removed by reaction for 2 min with 0.1 M NaOH in dioxane/methanol/water, (30:9:1, v:v:v). The couplings of the sterically hindered Aib residues were achieved by means of either BOP/DMAP activation or Fmoc‐Aib‐Cl. Acid deprotection of the peptide was performed by reaction with 50% TFA in CH2Cl2 for 30 min without significant cleavage of the acid‐labile Aib‐Pro and Aib‐Hyp peptide bonds.
Transannular Cyclizations of Medium‐Sized Cycloalkynes and Cycloalkynones Induced by Electro‐ and Photochemically Generated NO3 Radicals
Authors: Wille Uta , Plath Christian
Published: July 2007

Transannular radical cyclizations of medium‐sized cycloalkynes and cycloalkynones induced by addition of NO3 radicals to the C–C triple bond were studied. In the reaction of NO3 with medium‐sized cycloalkynes oxidation of the triple bond to a carbonyl group occurred and formation of cis‐fused bicyclic alkanones by transannular cyclization was observed. In the reaction of NO3 radicals with medium‐sized cycloalkynones α,β‐epoxy ketones were formed in a transannular reaction sequence which can be formally considered as a retro Eschenmoser‐Ohloff fragmentation reaction. The scope and limitations of these reactions are presented and reaction mechanisms are proposed.
The Effect of Pressure on the Cycloadditions of Cyanoacetylene to Furan Derivatives – [2.2](2,5)Furanoparacyclophane, [8](2,5)Furanophane, and Furan
Authors: Breitkopf Volker , Bubenitschek Peter , Hopf Henning , Jones Peter G. , Klärner Frank‐Gerrit , Schomburg Dietmar , Witulski Bernhard , Zimny Bernd
Published: July 2007

At 1 bar and 160°C the reaction of cyanoacetylene (1) with [2.2](2,5)furanoparacyclophane (3) produced the unexpected “ring‐enlarged” ketones 6–11. In the reaction of 1 with [8](2,5)furanophane (4) comparable products 21 and 22 were observed, in addition to the products 19 and 20 expected from a consecutive Diels‐Alder addition, Alder‐Rickert cleavage process and the Diels‐Alder addition of 1,4‐dicyano‐1,3‐cyclobutadiene (2a) to 4, respectively. In the reaction of 1 with the parent furan 5 only the (2:1) and (1:2) Diels‐Alder adducts 23, 25, 26, and 27 were found. High‐pressure experiments and the reactivity of 2‐cyano‐7‐oxabicyclo‐[2.2.1]hepta‐2,5‐diene (24), which was prepared independently by flow‐thermolysis of the (1:2) Diels‐Alder adducts 26 and 27, provide evidence that the (2:1) adducts 20, 23, and 13 are probably formed by a sequence of Diels‐Alder and [2 + 2] cycloadditions rather than by the reverse sequence starting with [2 + 2] cyclodimerization of 1 followed by Diels‐Alder reaction with cyclobutadiene 2a as postulated by the analogy to the trimerization of 1 and the cycloaddition of 1 to paracyclophane. The high‐pressure experiments led us to propose a new mechanism of formation of the “ringenlarged” ketones 6–11.
α‐Amino Acids and N‐Protected α‐Amino Aldehydes by Stereoselective Additions of a Chiral Vinyllithium Reagent to Sulfonylimines
Authors: Braun Manfred , Opdenbusch Kersten
Published: July 2007

The chiral vinyllithium reagent (S)‐1b, readily generated from dibromoalkene (S)‐1a by bromine/lithium exchange, adds stereoselectively to mesitylsulfonylimines 2a–f so that the diastereomers 3 are obtained in ⩾98% d.e. after column chromatography. The bromoalkenes 3a–d are submitted to ozonolysis in methanol to give α‐mesitylsulfonylamino esters (S)‐8a–d which can be hydrolyzed to deliver N‐protected α‐amino acids in >95% e.e. On the other hand, α‐mesitylsulfonylamino aldehydes 12a–d are available when bromoalkenes 3a, d–f are first debrominated (→ 11a–d) and subsequently ozonized. In order to avoid reacemization, the aldehydes 12a–d are not purified but submitted to a Mukaiyamatype aldol addition whereby hydroxyesters 15a–d are formed as single diastereomers in a chelate‐controlled reaction. The relative configuration of the esters 15a–d is proven by conversion into the oxazolidinones 16a–d whose optical purity is determined to exceed 92% e.e. by 1H‐NMR measurements in the presence of chiral shift reagents. The sulfonylimine 21a and a series of para‐substituted derivatives 21b–h are also allowed to react with the vinyllithium reagent 1b to give mixtures of diastereomers 22/23. The logarithms of the diastereomeric ratios 22:23 correlate with Hammett's σ‐values.
Convenient Syntheses of 2,3,4,6‐Tetra‐O‐Alkylated D‐Glucose and D‐Galactose
Authors: Käsbeck Ludwig , Kessler Horst
Published: July 2007

Convenient syntheses of the 2,3,4,6‐tetra‐O‐benzylated and ‐allylated D‐glucopyranoses 1 and 2 and the corresponding D‐galactopyranoses 3 and 4 are described. The D‐glucose derivatives 1 and 2 were obtained from inexpensive sucrose by peralkylation and subsequent acid hydrolysis. In this reaction sequence an alkylated D‐fructofuranosyl cation is generated which was trapped by different nucleophiles to afford 4‐benzyloxymethylenefurfural (8) and the alkylated D‐fructosides 7, 8 and 10. On the other hand 2,3,4,6‐tetra‐O‐benzyl‐D‐galactose 3 was synthesized by oxidative cleavage of ethyl 2,3,4,6‐tetra‐O‐benzyl‐1‐thio‐α,β‐D‐galactopyranoside (11) with aqueous N‐bromosuccinimide. The alternative route for the preparation of 2,3,4,6‐tetra‐O‐allyl‐D‐glucopyranoside (2) via p‐methoxybenzyl β‐D‐glucoside is less attractive. However, this route was used for the synthesis of 2,3,4,6‐tetra‐O‐allyl‐d‐galactose (4).
Synthesis of rac‐ar‐Curcumen‐15‐al
Authors: Weyerstahl Peter , Schlicht Volker
Published: July 2007

Starting from p‐tolunitrile (4) via alkylation with the bromoacetal 12 (→ 8), and with MeI (→ 9), hydrolysis to 10, Wittig reaction (→ 7) and DIBAH reduction, the rac‐ar‐curcumen‐15‐al (2) was obtained. The cumin‐like, citrus odor of rac‐2 is similar to that of the isolated (−)‐2.
1,3‐Dipolar Cycloadditions, 96. – Cycloadditions of Alicyclic Thione S‐Oxides with Alicyclic Thiones
Authors: Huisgen Rolf , Mloston Grzegorz , Polborn Kurt , Sustmann Reiner , Sicking Willi
Published: July 2007

Thione S‐oxides (sulfines) harbor the allyl anion MO of 1,3‐dipoles, but fail to undergo 1,3‐cycloadditions to the usual dipolarophiles with a CC multiple bond. Thioketones stand the test as superdipolarophiles. The thione S‐oxides 3 and 9 combined with the thioketones 5 and 7 at 80–100°C, furnishing spiro‐1,2,4‐oxadithiolanes in high yields despite steric hindrance. The structures of the cycloadducts were clarified by their spectra and an X‐ray analysis of 11. Becke3LYP/6‐31G* calculations of transition structures and products for the cycloadditions of thioformaldehyde S‐oxide to thioformaldehyde support the observed regiochemistry. The activation energy amounts to 3.9 kcal mol−1, in contrast to EA = 17.4 kcal mol−1 for the corresponding addition to ethylene. The transition structures are in accordance with concerted cycloadditions.
Palladium‐Catalyzed Synthesis of Propellanes with Hexaarylethane Structure
Authors: Dyker Gerald , Körning Jutta , Bubenitschek Peter , Jones Peter G.
Published: July 2007

Areno‐anellated [3.3.n]propellanes withn= 2, 3, and 4 are easily accesible by palladium‐catalyzed domino coupling processes of the pentalene system8with various aryl iodides. The X‐ray structure investigations reveled a noteworthy elongation of the central CC single bond of these propellanes to ca. 162 pm.
2(3H)‐Oxazolones from α‐Hydroxy Amides and Keteneylidenetriphenylphosphorane via a Phoshorus Ylide Cascade
Authors: Löffler Jonas , Schobert Rainer
Published: July 2007

Upon heating in xylene α‐hydroxyamides 3 react with the cumulated phosphorus ylide 1 to give the substituted 2(3H)‐oxazolones 8 in 40–80% yield. The reaction proceeds via an addition/cyclization/intermolecular‐Wittig olefination sequence, which implies three different types of phosphorus ylides of increasing “ylide activity”. Evidence for the proposed mechanism is provided by trapping the intermediate ylide species with suitable carbonyl compounds. This technique may also be used to exclusively prepare the 2,4‐oxazolidinediones 13 in good yields.
Reactions of Sodium Cyanodithioformate with Monosubstituted Hydrazines
Authors: Drexler Kerstin , Dehne Heinz , Reinke Helmut , Michalik Manfred
Published: July 2007

Sodium cyanodithioformate (1) reacts with methylhydrazine (2) only in the presence of H2S to give the new, zwitterionic thiooxamic acid 1‐(2‐methylhydrazide) 2‐(2‐methylhydrazone) (3) in good yield. The reaction of 1 with phenylhydrazine (5) gives a mixture of the zwitterionic thiooxamic acid 1‐(2‐phenylhydrazide) 2‐(2‐phenylhydrazone) (6b) and the non‐zwitterionic glyoxylamide bis(phenylhydrazone) (7). The mechanism of the formation of 3 and 6b is discussed. X‐ray structural data of 3 and 6b are given.
A Novel Pentaannulation Reaction of Iminium Ions
Authors: Ofial Armin R. , Mayr Herbert
Published: July 2007

The preformed iminium salts (1a–1d)‐SbCl react with (1,1‐dimethylallyl)trimethylsilane 2 in dichloromethane at ambient temperature to give the pyrrolidinium salts (3a–3d)‐SbCl in high yield. In addition, small amounts of the ene products 4c‐SbCl and 4d‐SbCl have also been detected.
Synthesis of Bicyclic Homochiral Dienes by Allylic Rearrangement of Cyclohexenols – Suitable Building Blocks for The Synthesis of Nagilactones
Authors: Westermann Bernhard , Dubberke Silke
Published: July 2007

A very short and straightforward synthesis towards highly functionalized dienes is described. The homochiral starting material, unsaturated β‐oxo ester 2, can be prepared by enzyme‐catalyzed saponification. The utility of the dienes has been demonstrated in a cycloaddition with N‐phenyltriazolidinone as the dienophile. The Diels‐Alder reaction is highly diastereoselective, yielding only one diastereomer.
Bicyclic and Tricyclic Compounds with β‐Amino Alcohol Groups as Chiral Ligands in the Enantioselective Reaction of Diethylzinc with Aldehydes
Authors: Aurich Hans Günter , Biesemeier Frank , Geiger Michael , Harms Klaus
Published: July 2007

Reduction of the enantiomerically pure allyloxy esters 9 or ent‐9 with DIBAH afforded the corresponding aldehydes which were treated in situ with chiral or achiral hydroxylamines 8 to give nitrones 10. These underwent a spontaneous intramolecular 1,3‐dipolar cycloaddition, affording the bicyclic compounds 11 and 12, respectively. In an analogous manner, a mixture of the tricyclic compounds 14 and 15 was prepared. Treatment of compound 16 with cyclohexene oxide afforded a mixture of diastereomers 17 and 18. Diastereomers 14 and 15 as well as 17 and 18 could be separated by chromatography. X‐ray analyses of compounds 11Ff, 17, and 11Af · HCl were performed. The bicyclic and tricyclic compounds were used as chiral ligands in the reaction of diethylzinc with aldehydes 19, in particular with benzaldehyde (19a). Using bicyclic compounds with a tertiary β‐hydroxyalkyl substitutent at the N atom as ligands, ee's in the range of 78 to 95% were found. Whereas for the best ligands 11Ae and Af the enantioselectivity in the reaction of 4‐tolualdehyde was only slightly decreased, with the aliphatic aldehydes 19c and d distinctly lower enantioselectivities were determined.
Synthese und Konformation von Hexahydro‐isochino[1,2‐b][3]benzazepinen
Authors: Clemens Martina , Meise Werner , Himmel Klaus , Jansen Martin
Published: July 2007

Synthesis and Conformation of Hexahydro‐isoquino[1.2.‐b][3]benzazepines

The synthesis of the six hexahydro‐isoquino[1,2‐b][3]benzazepines 13a–f is described; their conformation is investigated by NMR spectroscopic methods, X‐ray analysis and dehydrogenation with mercury(II) acetate.
An Intramolecular 1,3‐Dipolar Cycloaddition Involving One Alkyne and Two Nitrone Groups
Authors: Aurich Hans Günter , Biesemeier Frank , Harms Klaus
Published: July 2007

The chiral nonracemic compound 4 was prepared from ethyl (S)‐(–)‐lactate and 1,4‐dibromo‐2‐butyne. Reduction with DIBAH at −72°C and subsequent treatment of the resulting dialdehyde with N‐methylhydroxylamine yielded the dinitrone 5, which underwent two consecutive intramolecular cycloadditions to give the chiral nonracemic compound 7. The structure of 7 was confirmed by an X‐ray analysis. Reductive ring opening afforded compound 8.
Phenazin‐5(10H)‐yls, 5. – Intermolecular π‐π Interactions (Pimerization) oftert‐Butyl‐Substituted Phenazin‐5(10H)‐yl Radicals in The Solid State: Syntheses, Crystal Structures and Magnetic Susceptibility Measurements
Authors: Gleiter Marco R. , Kanellakopulos Basil , Krieger Claus , Neugebauer Franz A.
Published: July 2007

Introduction oftert‐butyl groups into the phenazine frame‐work was accomplished by treatment of 5‐acetyl‐5,10‐dihydrophenazine (2a) withtert‐butyl chloride in the presence of AlCl3. Starting from the 2,8‐ or 3,7‐di‐tert‐butyl‐substituted derivatives2cand2b, a series of phenazin‐5(10H)‐yl radicals (1c–i) was synthesized and characterized by ESR and EN‐DOR spectroscopy. With the exception of1c, all phenazin‐5(10H)‐yls were obtained in crystalline form, and for1d–fthe long‐wavelength absorption band at λ ≈ 870 nm indicates intermolecular π‐π interactions in the solid state. For1d,1eand1hthe crystal structure could be determined. The unit cell of1dconsists of eight phenazin‐5(10H)‐yls. Surprisingly, four of them are arranged in radical pairs, whereas the other four lie independently in the lattice. In agreement with this structure, the magnetic susceptibility results correspond to a content of 50% monoradical and an almost complete spinpairing in the radical pairs up toT= 220 K. In1e, the four phenazin‐5(10H)‐yls in the unit cell are arranged in two independent radical pairs,AandB, which are characterized by close interplanar distances and short intermolecular contacts between atoms with significant spin populations. Accordingly, the susceptibility data indicate strong spin‐pairing at low temperature. Due to extensive steric shielding of the phenazin‐5(10H)‐yl framework, the crystal structure of1hgives no evidence of any π‐π interactions between adjacent radicals. As expected, the magnetic susceptibility of1hcorresponds to that of an ordinary monoradical.
Reactions of 2‐(Organylseleno)propenenitriles with Dimethyl Ethynedicarboxylate
Authors: Döpp Dietrich , Sturm Thomas
Published: July 2007

(2‐tert‐Butylseleno)propenenitrile (12a) has been prepared and treated with dimethyl ethynedicarboxylate (3) and methyl propiolate (18) to give the 2,3‐dihydroselenophenes 16 and 21, respectively. In contrast, 2‐(ethylseleno)‐, 2‐(methylseleno)‐ and 2‐(phenylseleno)propenenitrile (12b–d) tend to form polysubstituted butadienes 17b–d with 3 by net organoylseleno group transfer from 12b–d to C‐2 of 3 following attachment of C‐3 of 17 to C‐3 of 3. Five‐membered selenonium ylides are proposed as intermediates.
Carbohydrate‐Based Crown Ethers
Authors: Miethchen Ralf , Fehring Volker
Published: July 2007

Chiral 12‐crown‐4 ethers (13–16) and 18‐crown‐6 ethers (21–24) containing two and three ethylene‐bridged D‐glucopyranose moieties, respectively, have been synthesized. 2‐O‐(Acetoxyethyl)‐3,4,6‐tri‐O‐benzoyl‐α‐D‐glucopyranosyl fluoride (5), generated by treatment of 2,3,4‐tri‐O‐benzoyl‐1,2‐O‐ethylene‐β‐D‐glucose (4) with HF/nitromethane/acetic anhydride was the key building block. It was used as a glycosyl donor and/or – after modification – as an acceptor component in head‐to‐tail‐type glycosylations. Thus, the openchain precursors 9/11, 10/12, 17/18 and 19/20 of the crown ethers were prepared from reaction of 5 with 7, 11 and 12, respectively, in BF3‐catalyzed glycosylations. The stereoselectivity of the glycosylations could be influenced by the use of different solvents. α‐Selective syntheses of the crown ethers 14 (from the thioglycoside 11) and 23 (from the thioglycoside 20) were achieved in dichloromethane using NIS/trifluoromethanesulfonic acid for activation. In acetonitrile, the thioglycoside 11 yielded predominantly the 12‐crown‐4 ether 13, while thioglycoside 18 formed a mixture of the α‐and β‐anomers 21 and 22 under the same activation conditions.
Synthesis and Application of Isothiocyanato Derivatives of Nucleosides
Authors: Zehl Andrea , Cech Dieter
Published: July 2007

3′‐Deoxy‐3′‐isothiocyanatothymidine (4), 3′,5′‐protected 2′‐deoxy‐2′‐isothiocyanatouridine (8), and 2′,3′‐dideoxy‐2′‐isothiocyanatouridine (14), respectively, have been prepared from the corresponding 2′‐ or 3′‐amino derivatives. SnCl2, Bu3SnH, and dithiothreitol were employed to reduce the 2′‐ or 3′‐azido derivatives to give the aminonucleosides which served as starting materials for the thiocarbonylation. Thiocarbonylation, by either a mixture of carbon disulfide and mercuric oxide or N,N′‐thiocarbonyldiimidazole, leads directly to the target molecules in high yields. Furthermore, the direct transformation of azidonucleosides into the corresponding isothiocyanto derivatives via treatment of phosphanimine nucleosides with CS2 is described. Th activity of the isothiocyanate group is used for covalent coupling of different linking molecules or dyes to the carbohydrate moiety of the nucleosides.
Regioselective Olefination of Cross‐Conjugated 3‐Thioxosteroids by [3+2] Cycloaddition
Authors: Fiedler Beate , Weiß Dieter , Beckert Rainer
Published: July 2007

Reaction of 3‐thioxoandrosta‐1,4‐dien‐17‐one (1) with the diazo compounds 2a–i affords 4′‐substituted spiro[17‐oxoandrosta‐1,4‐diene‐3,2′‐[1,3,4]thiadiazolines], which undergo a two‐step ring contraction with extrusion of nitrogen and sulfur, leading to the substituted 3‐methylen‐ and 3‐propylidenandrosta‐1,4‐dien‐17‐ones 3a–i in good yields.
Synthetic Microbial Chemistry, XXX. Synthesis of Acetophthalidin, a Fungal Metabolite which Inhibits the Progression of the Mammalian Cell Cycle
Authors: Nomoto Shin , Mori Kenji
Published: July 2007

Acetophthalidin [(±)‐3‐acetyl‐5,7‐dihydroxyphthalide (1)] was synthesized from 6,8‐diacetoxy‐3‐methylisocoumarin (8) by its epoxidation followed by hydrolysis.
Thermal and Electron Transfer Induced Reactions of Enediynes and Enyne‐Allenes, 5. First Isolation of Two Rotamers About the PC Bond in a Phosphane Oxide
Authors: Schmittel Michael , Kiau Susanne
Published: July 2007

The thermal cyclization of the phosphane oxide substituted enyne‐allene 1d results in the formation of 4d, an unknown double‐bond shift isomer of the 11H‐benzo[b]fluorene system. Because of the completely hindered rotation about the PC bond, two rotamers could be isolated and identified on the basis of their spectral data. No thermal interconversion between the two rotamers was observed.
Flash‐Vacuum Pyrolysis of Stabilised Phosphorus Ylides, 9. Preparation and pyrolysis of β,γ‐dioxo ylides, β,β′,γ,γ′‐Tetraoxo Ylides and Hexaoxo Bis(ylides)
Authors: Aitken R. Alan , Karodia Nazira
Published: July 2007

Six examples of the β,β′,γ,γ′‐tetraoxo phosphorus ylides 6 have been prepared. While they are found, upon flash‐vacuum pyrolysis (FVP) at 500°C to decompose to give no useful products, conventional pyrolysis by distillation at 200°C gives the trioxo alkynes 12 and 13 where R1 and R2 are alkoxy groups. Three examples of the previously unknown hexaoxo bis(ylides) 7 have been obtained but, with eight contiguous C=X functions, these are too fragile to give any useful product upon FVP. The pyrolysis of the simpler β,γ‐dioxo ylides 9 used to prepare 6 and 7 has also been examined for the first time and at 600°C it gives the alkynes 11 in low yield for R1 = OMe or OEt but not Ph. The fully assigned 13C‐NMR spectra of all the ylides 6, 7, and 9 are presented.
Enzymatic Synthesis of Peptide Conjugates: Tools for the Study of Biological Signal Transduction
Authors: Kappes Thomas , Waldmann Herbert
Published: July 2007

Glyco‐, phospho‐, nucleo‐ and lipoproteins play key roles in biological signalling cascades, by which chemical signals are passed across the cell membrane and further to the cell nucleus. For the study of the biological phenomena associated with these protein conjugates, structurally well‐defined peptides containing the characteristic linkage region of the peptide backbone with the carbohydrate, the lipid or the phosphoric acid ester can be applied advantageously. The multifunctionality and the pronounced acid‐ and base‐lability of lipo‐, phospho‐, nucleo‐ and glycopeptides, however, renders their synthesis a formidable challenge to conventional organic synthesis. This review highlights the potential of enzymatic transformations, in particular for the removal of protecting groups, as central techniques for the construction of complex and sensitive biologically relevant peptide conjugates under particularly mild conditions and with high selectivity.
Pheromone Synthesis, CLXXX. Synthesis of (3S,11S)‐3,11‐Dimethyl‐2‐heptacosannone, a New Component of the Female Sex Pheromone of the German Cockroach
Authors: Takikawa Hirosato , Fujita Ken , Mori Kenji
Published: July 2007

(3S,11S)‐3,11‐Dimethyl‐2‐heptacosanone (1), a new and the fourth component of the female sex pheromone of Blattella germanica, was synthesized by starting from ethyl (R)‐3‐hydroxybutanoate (2) and (R)‐citronellol (3).
A Facile Asymmetric Synthesis of the Compactin Lactone Moiety
Authors: Schabbert Silke , Tiedemann Ralf , Schaumann Ernst
Published: July 2007

Starting from (R)‐O‐benzylglycidol and a sulfur‐stabilized allyl anion, a (3 + 3) synthesis of the α,β‐unsaturated (6S)‐δ‐lactone 7 is achieved. Subsequent diastereoselective addition of a phenyldimethylsilyl cuprate and unmasking of the latent hydroxy function provides the lactone unit of compactin.
Efficient Biomimetic Synthesis of Indole Alkaloids of the Vallesiachotamine Group by a Domino Knoevenagel Hetero Diels‐Alder Hydrogenation Sequence
Authors: Tietze Lutz F. , Bachmann Jürgen , Wichmann Jürgen , Zhou Yifa , Raschke Thomas
Published: July 2007

An efficient three‐step biomimetic synthesis of the four diastereomeric 18,19‐dihydroantirhines 4a–d starting from the tetrahydrocarboline aldehydes 5a and 5b is described. Domino reaction of the aldehydes 5a and 5b, respectively, with Meldrum's acid (6) and the enol ethers 8a and 8b in the presence of catalytic amounts of ethylenediammonium diacetate leads to the strictosidine analogues 10a–d and 11a–h, respectively, in 74–86% yield, hydrogenation of which gives mainly 15 and 16 with the skeleton of the vallesiachotamine indole alkaloids (55–86%). In addition, small amounts of 17 and 18 with the corynanthe skeleton are also formed (10–12%). Reduction of both 15 and 16 with LiAlH4 yields the diastereomeric rac‐18,19‐dihydroantirhines 4a–d in 78–86% yield.
2,5‐Bisdiazomethylfuran: A Novel Entry to the C6H4O Surface
Authors: Sander Wolfram , Albers Reinhard , Komnick Peter , Wandel Holger
Published: July 2007

Warming the dilithium salt 7 of furan‐2,5‐dicarboxaldehyde bis(tosylhydrazone) to 110°C and subsequently trapping the products in solid argon at 10 K resulted in the formation of 1‐diazo‐hex‐3‐en‐5‐yn‐2‐one (9). The intermediate 2,5‐bis(diazomethylfuran) (6) is too labile to be directly observed under these conditions. The formation of 9 from 6 is rationalized by the loss of one nitrogen molecule and rapid rearrangement of the intermediate carbene 8. Photolysis of 9 leads to loss of the second nitrogen molecule and rearrangement of the resulting carbene 12. The major path is the Wolff rearrangement to hexa‐1,3‐dien‐5‐yn‐1‐one (11); the minor path is the intramolecular cycloaddition of the carbene center to the triple bond to 1H‐bicyclo[3.1.0]hexa‐3,5‐dien‐2‐one (2). UV photolysis of 2 results in the ring opening to yield again ketene 11. The mechanism of this rearrangement was investigated by deuterium labeling.
Chemo‐, Regio‐, and Stereoselective Diels–Alder Reaction of Ambident Dienophilic Monothiomaleimide
Authors: Tamaru Yoshinao , Harayama Hiroto , Sakata Hiroya , Konishi Hironobu , Fugami Keigo , Kimura Masanari , Tanaka Shuji , Okajima Toshiya , Fukazawa Yoshimasa
Published: July 2007

Both the CS and CC functionalities of N‐arylmonothiomaleimides readily undergo a [4 + 2] cycloaddition reaction at ambient temperatures with both electron‐donating and ‐withdrawing dienes. The CS groups of N‐arylmonothiomaleimides are generally more reactive than the CC groups, especially toward dienes bearing conjugation and electron‐attracting groups, and provide mixtures of ortho,endo products 3 and ortho,exo products 4 with complete regioselectivity (100% ortho) and with high stereoselectivity (more than 86% endo). The CC groups, on the other hand, display a high stereoselectivity (100% endo) but a low regioselectivity, providing ortho,endo adducts 5 and meta,endo adducts 6 in ratios ranging from 1:1 to 6:1. Compared with N‐phenylmonothiomaleimide (1). N‐p‐nitrophenylmonothiomaleimide (11a) is more reactive and displays a higher CS vs. CC chemoselectivity in favor of CS, while N‐p‐anisyl (11b) and N‐benzyl (11c) derivatives display quite the reverse reactivity and selectivity. N‐Phenylmonothiocitraconimide (11d) serves as a CS specific dienophile and reacts with dienes to furnish ortho,endo adducts 12 with excellent regio‐ and stereoselectivities (100% ortho,endo). Both hard (BF3 · OEt2, TiCl4) and soft (CuBr · SMe2) Lewis acids enhance the reaction rate enormously and increase chemoselectivity in favor of CS. The chemo‐ (CS/CC), regio‐ (ortho/meta) and stereochemical outcomes (endo/exo) are rationalized by transition structure analysis based on AM1 calculation.
Biologically Active Glycosides from Asteroidea, 36. Re‐examination of the Structure of Acanthaganglioside C, and the Identification of Three Minor Acanthagangliosides F, G and H
Authors: Miyamoto Tomofumi , Inagaki Masanori , Isobe Ryuichi , Tanaka Yoshitsugu , Higuchi Ryuichi , Iha Masahiko , Teruya Kiichi
Published: July 2007

The structure of acanthaganglioside C (1) has been re‐examined using MQ‐COSY, TOCSY, NOESY, HSQC, HMBC and HSQC‐TOCSY experiments. As a result, it is clarified that N‐acetyl neuraminic acid (NeuAc) is linked to the C‐3 position, and not the C‐4 position, of the β‐galactopyranose. In addition, three minor acanthagangliosides, F (2), G (3) and H (4), have also been isolated from the ganglioside molecular species AG‐2. Their structures have been determined on the basis of chemical and spectroscopic evidence.
Bis(guanidinium) Receptors as Ribonuclease Active‐Site Model Systems: Structural Changes and Solvent Effects
Authors: Oost Thorsten , Filippazzi Anna , Kalesse Markus
Published: July 2007

Various bis(guanidinium) compounds have been synthesized and their abilities to cleave the RNA model compound HPNPP have been tested in acetonitrile and in water. Depending on the spacer length, the substitution of the guanidinium groups, and the presence of an internal base, different rate constants for the transesterification of HPNPP are observed in these two media. The steroid derived bis(guanidinium) compound 12 was identified as a superior system.
Stereoselective Alkylation of Sulfoxides and Sulfones Derived from (R)‐Cysteine
Authors: Dehmlow Eckehard Volker , Pieper Stefanie , Neumann Beate , Stammler Hans‐Georg
Published: July 2007

(R)‐Cysteinol was protected as its oxazoline derivatives 1a–c and oxidized to the sulfoxides 2, 3 and the sulfone 7. These compounds could be alkylated under chelate control to give tertiary and quaternary stereogenic centers in a highly stereoselective manner to yield 4a–c,5, 8a–c, 11 and 12. Starting with the sulfone 7, both configurations at the new chiral center can be constructed.
Pheromone Synthesis, CLXXXIV. Synthesis and Absolute Configuration of Sordidin, the Male‐Produced Aggregation Pheromone of the Banana Weevil, cosmopolites sordidus
Authors: Nakayama TǑRu , Mori Kenji
Published: July 2007

The racemate as well as both the enantiomers of sordidin (1‐ethyl‐3,5,7‐trimethyl‐2,8‐dioxabicyclo[3.2.1])octane were synthesized, and the natural pheromone was shown to be (1S,3R,5R,7S)‐(+)‐1.
Synthesis of γ‐Unsaturated Enamides by N‐Acylation of Imines Derived from γ‐Unsaturated Amines
Authors: Meuzelaar Gerrit J. , Van Vliet Michiel C. A. , Neeleman Ernst , Maat Leendert , Sheldon Roger A.
Published: July 2007

N‐Formyl‐N‐styryl amines (1–3) were prepared from imines derived from γ‐unsaturated amines and phenylacetaldehyde by formylation with ethyl formate in the presence of sodium methoxide. Formation of the corresponding N‐acetyl analogues was less selective, as was demonstrated by reaction of N‐[2‐(cyclohexen‐1‐yl)ethyl]‐2‐(phenyl)ethylidenimine and acetyl chloride. Some N‐acetyl‐N‐vinyl amines (7, 11) were prepared from the corresponding imines by acetylation with acetyl chloride or acetic anhydride. N‐Formyl‐N‐vinyl amines (12, 13) were synthesized from the appropriate imines using acetic formic anhydride as formylating agent.
Pyridinium N‐Phenoxide Betaines and Their Application to the Characterization of Solvent Polarities, XXIII. Determination of ET(30) Values of Supercritical Carbon Dioxide at Various Pressures and Temperatures
Authors: Eberhardt Runar , Löbbecke Stefan , Neidhart Bernd , Reichardt Christian
Published: July 2007

By means of the negative solvatochromic betaine dyes 1a, b, the UV/Vis‐spectroscopically derived empirical solvent polarity parameter ET(30) for supercritical carbon dioxide (sc‐CO2) was determined in the temperature and pressure ranges 40–80°C and 150–550 bar, respectively.
A General Method for the Synthesis of C‐Glycosides of Nojirimycin
Authors: Fuchss Thomas , Streicher Hansjörg , Schmidt Richard R.
Published: July 2007

Methyl 2,3,4,6‐tetra‐O‐acetyl‐N‐(benzyloxycarbonyl)nojirimycin (3) can be readily transformed into the corresponding azaglycal 6 or fluoride 7, which are versatile glycosyl/piperidinosyl donors. Reaction of 7 with allyltrimethylsilane, propinyltrimethylsilane, trimethylsilyl cyanide, and trimethylsilyl enol ether as carbon nucleophiles, afforded, in the presence of BF3 · OEt2 as catalyst, the corresponding C‐glycosides 8–10 and 12–14 in good yields. The anomeric configurations of the C‐glycosides are ascertained with the help of ROESY‐NMR data.
Bicyclo[4.4.0]deca‐1,6‐diene‐2,7‐diyl: A 1,4‐Didehydrobutadiene Derivative
Authors: Roth Wolfgang. R. , Wasser Thorsten , Gleiter Rolf , Weigl Hagen
Published: July 2007

From the NO‐ and O2‐dependence of the trapping rate of 1,6‐cyclodecadiyne (3) in the gas phase and in supercritical CO2 in the temperature range 160–290°C, the enthalpy profile for the equilibrium 3 ⇌ 4 has been established. For the diradical 4, a heat of formation of 116.2 kcal · mol−1 is obtained, which agrees well with the expectation value derived by the abstraction of two hydrogen atoms from hexahydronaphthalene (5).
Ozonolyses of O‐Alkylated Ketoximes in the Presence of Carbonyl Groups: A Facile Access to Ozonides
Authors: Griesbaum Karl , Liu Xuejun , Kassiaris Athanassios , Scherer Martin
Published: July 2007

Ozonolyses of O‐methyl oximes of acyclic ketones (7, 10, 19) and of cyclic ketones (16, 24, 27, 31) in the presence of acyclic ketones (8, 9, 17) or of cyclic ketones (18, 25, 26, 31) gave the corresponding tetrasubstituted cross‐ozonides (13, 21, 29, 32). Ozonolyses of O‐methylated monooximes of 1,4‐, 1,5‐, and 1,6‐dicarbonyl compounds (35b–f) gave the corresponding bicyclic ozonides 36b–f.
Diastereo‐ and Regioselective Intramolecular Heck Reaction of α‐Amino Alcohol Derivatives for the Synthesis of Enantiomerically Pure Isoquinolines and Benzazepines at Ambient and High Pressure
Authors: Tietze Lutz F. , Burkhardt Olaf , Henrich Marielouise
Published: July 2007

Alkylation and acylation of the alkenes 9b, c and 10a, b, which are easily prepared from the corresponding α‐amino alcohols, with 2‐halobenzyl and 2‐halobenzoyl halides respectively, gives 11–15. These compounds cyclize with excellent diastereo‐ and regioselectivity to the enantiomerically pure N‐heterocycles 18–20 in an intramolecular Heck reaction using 5 mol‐% of Pd(OAc)2 in the presence of PPh3, TPAB and KOAc. Under the same conditions substrate 17 leads to the enantiomerically pure benzazepine 24. The reaction of the bromoarene derivatives 14–15 must be performed under high pressure to give good results.
Facile Preparation of Novel Nonracemic Oxy‐Substituted Cyclopropanone S,S‐Acetals by γ‐Cyclisation of Glyceric Aldehyde Dithioacetal Derivatives and Studies of their Reactivity
Authors: Schwarz Hans‐Georg , Dreeßen Sylvia , Tersakian Ani , Schaumann Ernst
Published: July 2007

Easily available glyceric aldehyde dithioacetals, (R)‐1 and (R)‐2, are converted via their tosylates, (R)‐7a and b, and γ‐elimination into nonracemic oxy‐substituted cyclopropanone S,S‐acetals, (R)‐12 and (R)‐13, in the presence of suitable electrophiles for trapping of alkoxide intermediates. Treatment of cyclopropanol (R)‐14 with Burgess' reagent causes no 1,2‐elimination, but a remarkable SN etherification with retention of configuration.
Regioselective Reductive Ring Opening of 2‐(2‐Hydroxyphenyl)‐3‐[(trimethylsilyl)oxy]oxetanes at the More Substituted C‐2 Position
Authors: Bach Thorsten , Eilers Frank , Kather Kristian
Published: July 2007

The title compounds 7 were prepared in situ by deprotection of the corresponding pivaloyl‐substituted oxetanes 3 with lithium aluminium hydride in tetrahydrofuran. under these conditions a reductive ring opening at c‐2 (hydrodealkoxylation) occurred which was initiated by a nucleophilic hydride attack and which yielded the triols 8 (64–85%). the facility of the reaction and its high regioselectivity can be explained by the directing ability of the hydroxy group at the aromatic substituent. The reaction proceeds stereospecifically, as shown by deuterium labelling experiments. The prerequisite 2‐(2‐pivaloyloxyphenyl)‐3‐[(trimethylsilyl)oxy]oxetanes 3 were prepared by the Paternò‐Büchi reaction of the protected salicylaldehyde 1 and various silyl enol ethers 2. The 2‐hydroxyphenyl substituent at the C‐3 position of oxetane 6 directed the hydride attack to the C‐4 position and yielded the triol 10 in 85% yield.
Chemical and Spectroscopical Properties of Medium Sized trans‐ and cis‐Bicyclo[n.1.0]alk‐2‐ynes
Authors: Detert Heiner , Meier Herbert
Published: July 2007

Chemical and spectroscopical properties of cis‐ and trans‐cyclopropano‐anellated cycloalkynes of medium ring size are investigated and compared with results from force field calculations. IR and 13C‐NMR data of the alkynes reflect the deformation of the triple bond due to ring strain. Parallel to bending the reactivity increases with decreasing ring size, the trans fused alkynes prove to be nearly as reactive as the cis fused with a two carbon smaller ring size. The bicycloalkynes are complexed with silver triflate. 13C NMR reveals that the triple bond as well as the cyclopropane serve as ligands.
The Paternò‐Büchi Reaction of 3‐Heteroatom‐Substituted Alkenes as A Stereoselective Entry to Polyfunctional Cyclic and Acyclic Molecules
Authors: Bach Thorsten
Published: July 2007

The preparation of 3‐heteroatom‐substituted oxetanes by the Paternò‐Büchi reaction, and their application in synthesis are reviewed. 3‐Oxetanols and 3‐aminooxetanes are the two most important oxetanes in this respect. By tuning the electronic properties of the enol and enamine substrates, a successful photocycloaddition to carbonyl compounds, with high yield, is possible. Since the oxetane formation proceeds stereoselectively, diastereomerically pure products are readily accessible, which can then be used in further transformations. To this end, regioselective ring‐opening reactions have been developed, some of which will be discussed in this account.
1,3‐Dipolar Cycloadditions, 100. Nitrones and Electrophilic Acetylenes; a New Rearrangement of 2,3‐Dihydroisoxazoles
Authors: Huisgen Rolf , Giera Henry , Polborn Kurt
Published: July 2007

The readiness of 4‐isoxazolines, the 1,3‐cycloadducts of nitrones to acetylenic compounds, to undergo rearrangement is notorious. The cycloadducts of the ketonitrones 5 and 6 to dimethyl acetylenedicarboxylate, dicyanoacetylene, and methyl propiolate were isolated and characterized. The 4‐isoxazolines 7 and 8 harbor the tetramethylcyclobutanone ring; they isomerize (7 at 45°C, 8 at −10°C) to enamine β‐carbonyl compounds 16 and 17 which are derived from the ring‐enlarged tetramethylpyrrolidin‐3‐one. The structure of 16 was elucidated by X‐ray analysis.
Asymmetric Induction Effects in the Preparation of Penicillin‐Analogous Thiazepines
Authors: Klar Bernhard , Imming Peter
Published: July 2007

N‐Acyldehydroalanines 3 react with cysteine and penicillamine esters to give a single diastereomer of the thiazepines 6. By modifying this reaction, the requirements for steric control were elucidated and a series of penicillin analogs 6 and 12 prepared.
Solvent Effects in [4+2] Cycloadditions of Polyhalogenated Cyclopentadienes with 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione
Authors: Sauer Jürgen , Schuhbauer Hans Markus
Published: July 2007

Relative rates of [4 + 2] cycloadditions of cyclopentadienes 1a–1e with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione (2) in 12 different solvents vary by factors of up to 19000, but the reactions show similar solvent effects. Rate constants k2 correlate well with solvent parameters AN (positive correlation) and DN, SB (negative correlations), but not with ET values.
Flexible Molecules with Defined Shape, VII. Conformational Analysis of 3,5‐Dimethylhexene Derivatives, Subunits of Polyketide Derived Natural Products
Authors: Göttlich Richard , Schopfer Ulrich , Stahl Martin , Hoffmann Reinhard W.
Published: July 2007

2,4‐Dimethylpentane (1) is a typical biconformational backbone segment. When one methyl group in 1 is replaced by a sp2 bound residue (vinyl, formyl, phenyl), as in compounds 3–6, a small preference for conformer 2b ensues, in which the sp2 bound group resides in the sterically more hindered position. Oxygen substituents in the 3‐position do not change this conformational preference, but in concert with bulkier sp2‐hybridized groups in the 2‐position, a preference for the 2a backbone conformation may be induced, in which the sp2‐hybridized group is in the less sterically hindered end‐of‐chain position, cf. compounds 20 and 23.
Synthesis of Substituted 1,2‐Dihydro‐2‐imino‐7‐methyl‐1,6(6H)‐naphthyridin‐5‐ones
Authors: Ivanov Ivo Christov , Stoyanov Edmont Vassilev , Denkova Pavletta Stoyanova , Dimitrov Valentin Stefanov
Published: July 2007

Vilsmeier formylation of the 4‐amino‐2‐pyridinones 4a–d leads to the formation of the corresponding 3‐carbaldehydes 5a–d (the diformylated product 8 is isolated as a by‐product). A cyclizing Knoevenagel reaction of 5 with CH‐acidic nitriles 6 in the presence of piperidine gives substituted 2‐imino‐1,6(6H)‐naphthyridin‐5‐ones 7a–p which have been shown by means of 1H‐NMR and 1H‐NOE measurements not to rearrange to 9. The products 7 are resistant against hydrolysis and only the ester group can be hydrolysed to an acid, 7q. Compounds 7c, d, f display in vitro antituberculosis activity.
Organophosphorus Compounds, 121. Phosphaalkynes in Ene Reactions with Alkylidenecyclopropanes and Allenes
Authors: Mackewitz Thomas W. , Ullrich Dietmar , Bergsträßer Uwe , Leininger Stefan , Regitz Manfred
Published: July 2007

Phosphaalkynes readily participate in ene reactions both with alkylidenecyclopropanes and with allenes to furnish phosphaalkenes (the products of a simple ene reaction) and phosphanes (the products of a tandem ene reaction). Thus, irrespective of the stoichiometry, the thermal reactions of the phosphaalkynes 1a‐c with isopropylidenecyclopropane (8) or cyclopropylidenecyclopentane (11) proceed by a tandem ene process with retention of the three‐membered ring unit to furnish the corresponding bis(cyclopropyl)phosphanes 10a‐c or 12. In contrast, with cyclopropylidenecyclohexane (13) as the H‐donor, the specific formation of either the monoadducts 14a,c or of the bisadducts 15a,c can be controlled. A crystal structure analysis of 15a confirmed the structures of the tandem ene products while the constitutions and configurations of the novel P‐cyclopropylphosphaalkenes 14a,c were unequivocally elucidated by an X‐ray crystal structure analysis of the corresponding, W(CO)5‐complexed system 16. Alkylated allenes such as 1,1‐dimethylallene (17), vinylidenecyclohexane (20), tetramethylallene (22), or 1,2‐cyclononadiene (24) undergo thermal addition by way of a double ene process to afford the phosphaalkynes 1. In each case, regiospecific attack of the phosphorus atom at the central C‐atom of the cumulene system results in the formation of the structurally unique phosphanes 21, 23a,b, and 25a,b. On the other hand, thermal reactions of 1a,b in the presence of 1,1‐diethylallene (26) come to a standstill after the first ene addition and furnish the cross‐conjugated phosphatrienes 27a,b as the first representatives of the previously unknown phospha[3]dendralene system. The thermally initiated tandem ene reactions of the phosphaalkynes 1 with propadiene (28) or tert‐butylallene (30) each proceed through transfer of a vinylic hydrogen atom from the ene to the enophile to afford the bis(propargyl)phosphanes 29a,b and 31, respectively, as addition products.