bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract(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

AbstractStarting 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

AbstractAn 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

AbstractWarming 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

AbstractBoth 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

AbstractThe 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

AbstractVarious 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

Abstract(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

AbstractThe 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

AbstractN‐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

AbstractBy 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

AbstractMethyl 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

AbstractFrom 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

AbstractOzonolyses 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

AbstractAlkylation 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

AbstractEasily 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

AbstractThe 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

AbstractChemical 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

AbstractThe 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

AbstractThe 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

AbstractN‐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

AbstractRelative 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

Abstract2,4‐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

AbstractVilsmeier 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

AbstractPhosphaalkynes 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.
Singlet Oxygen Quenching Abilities of Carotenoids
Authors: Baltschun Dietmar , Beutner Stefan , Briviba Karlis , Martin Hans‐Dieter , Paust Joachim , Peters Manfred , Röver Stephan , Sies Helmut , Stahl Wilhelm , Steigel Alois , Stenhorst Frank 
Published: July 2007

AbstractThe bimolecular rate constantskqfor quenching of singlet oxygen (1Δgstate) by 26 different natural and novel synthetic carotenoids were determined at 37 °C in a mixture of chloroform and ethanol. The steady‐state technique used involves the generation of1O2by thermal decomposition of disodium 3,3′‐naphtalene‐1,4‐diyl‐dipropionate endoperoxide (NDPO2) and the detection of its luminescence intensity at 1270 nm. Excitation energies (π,π*, 11Ag → 11Bu) and absorption maxima (430–590 nm) vary in the broadest range. Deeply coloured blue carotenoids are also included in the studies for the first time. An empirical correlation between the π,π* (11Ag→ 11Bu) excitation energy and carotenoid structure (effective chain lengthNeff) was found:E(S) = 12642 cm−1+ 92027 cm−1× 1/Neff. The quenching ability of the investigated carotenoids depends on the excitation energy of their transition at long wavelengths in a characteristic way showing as limiting factors either the thermal Arrhenius activation or the diffusion‐controlled rate. This dependence and the suspected relationship between singletE(S) and tripletE(T) energies, respectively, are discussed.
Supramolecular Adducts of Ferrocene and Five Bile Acid Derived Triolides
Authors: Lappalainen Kari , Kolehmainen Erkki 
Published: July 2007

AbstractFormation of supramolecular adducts of ferrocene (guest) and cyclic head‐to‐tail trimers (hosts) derived from bile acid: 3α‐hydroxy‐5β‐cholan‐24‐oic acid triolide (1), 3α‐hydroxy‐7‐oxo‐5β‐cholan‐24‐oic acid triolide (2), 3α‐hydroxy‐12‐oxo‐5β‐cholan‐24‐oic acid triolide (3), 3α‐hydroxy‐7α‐trifluoroacetoxy‐6β‐cholan‐24‐oic acid triolide (4) and 3α‐hydroxy‐12α‐TFA‐5β‐cholan‐24‐oic acid triolide (5) (TFA = trifluoroacetoxy) have been studied by 1H NMR. The best computer‐assisted data fitting on the 1H‐NMR chemical shift data was given by a 1:2 (guest/host) association model. The association constants vary in the range 170–990 M−1, 7‐oxo‐substituted triolide 2 and 12α‐TFA triolide 5 showing the largest and smallest values respectively. Generally, triolides bearing substituents at the position C‐7 (2 and 4), when compared with the 12‐substituted derivatives 3 and 5, seem to favour adduct formation, while a TFA group at the position C‐7 or C‐12 seems to hinder the adduct formation in comparison with the oxo‐substituted congeneers. This finding may be accounted for by the bulky character of the TFA group when compared to the oxo group.
Rearrangement Reactions, 6. New Functionalized Allenes: Synthesis Using Sigmatropic Rearrangements and Unusual Reactivity
Authors: Banert Klaus 
Published: July 2007

AbstractThe present article summarizes the synthesis of allenes, which bear a functional group with at least two heteroatoms, by [2,3] or [3,3] sigmatropic rearrangements of appropriate propargyl precursors. Recently, this method has been extended to prepare new types of functionalized allenes such as isocyanates, isothiocyanates, isoselenocyanates, azides, thiocarbonates, and azo compounds. The title compounds are very reactive as shown by rapid intra‐ and intermolecular consecutive reactions. This reactivity can be used to synthesize heterocycles and doubly functionalized 1,3‐butadienes.