bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hormone‐Receptor Interactions. Carboranylalanine (Car) as a Phenylalanine Analogue: Reactions with Chymotrypsin
Authors: Fischli Walter , Leukart Othmar , Schwyzer Robert 
Published: December 2004

AbstractIn order to test the effects of the replacement of phenylalanine by carboranylalanine (Car) in biological ligand‐acceptor interactions, Z · Ala‐Ala‐Car · OH (1) and Ac · Car · OEt (2) were synthesized and their reactions with chymotrypsin studied. The two compounds proved to be good inhibitors with K(i) values of 3 · 10−4M (1) and 8.6 · 104M (2); the K(i) of Z · Ala‐Ala‐Phe · OH (1a) is 1 · 10−3M. The inhibition constants were determined by a new photolytic technique, inhibition of photoaffinity labelling by Z · Ala‐Ala‐Phe(pN3) · OH. Ac · Car · OEt is not hydrolysed by chymotrypsin. The findings indicate that the carboranyl group can interact with the ‘phenyl recognition site’ of the enzyme to produce the binding that is characteristic of aromatic amino acid residues. However, some kind of distortion in the region of the ‘mechanistic site’ must be postulated in order to account for the failure of hydrolysis. Some possible effects of the replacement of aromatic amino acids by Car in peptide hormones on hormone‐receptor interactions are discussed.
Synthesis of 4‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐pentanal and its Conversion into Derivatives of Spiro[4.5]decane and of 1,6,7,7a‐Tetrahydro‐2H‐indene
Authors: Goldberg Ora , Dreiding André S. 
Published: December 2004

Synthese von 4‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐pentanal und dessen Umwandlung in Spiro[4.5]decan‐ und 1,6,7,7a‐Tetrahydro‐2H‐inden‐DerivateEs wird die Synthese von 4‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐pentanal als ein (1:1)‐Gemisch von zwei Diastereoisomeren 10A und 10B auf folgendem Weg beschrieben: Die Umsetzung des Grignard‐Reagens von 1,1‐Äthylendioxy‐3‐brom‐propan (2) mit 2‐Methoxy‐4‐methyl‐acetophenon (1) ergab 1,1‐Äthylendioxy‐4‐hydroxy‐4‐(2′‐methoxy‐4′‐methyl‐phenyl)‐pentan (3), welches sich mit methanolischer Salzsäure in 2‐Methoxy‐5‐(2′‐methoxy‐4′‐methyl‐phenyl)‐5‐methyl‐tetrahydrofuran (7A,B) umwandeln liess. Durch Birch‐Reduktion von 7A,B wurde 4‐(2′‐Methoxy‐4′‐methyl‐cyclohexa‐1′,4′‐dien‐1′‐yl)‐pentan‐1‐ol (8), und danach durch milde Hydrolyse 4‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐pentan‐1‐ol (9A,B)2 erhalten. Oxydation von 9A,B lieferte schliesslich den erwähnten Keto‐aldehyd 10A,B. Einige Produkte von Nebenreaktionen, nämlich 4, 5, 11, 12 und 13A,B, sind auch beschrieben.Der Keto‐aldehyd 10A,B liess sich in ein Gemisch, bestehend aus drei Diastereo‐isomeren A, B und C von 1‐Hydroxy‐4,8‐dimethyl‐spiro[4.5] dec‐7‐en‐6‐on (15) und aus zwei Diastereoisomeren A und B von 1,5‐Dimethyl‐1,6,7,7a‐tetrahydro‐2H‐inden‐3‐carbaldehyd (14), umwandeln. Für diese aldolartigen Cyclisierungen wurden vier verschiedene Methoden verwendet: (a) Stehenlassen in Tetrachlorkohlenstoff‐lösung, (b) Behandlung mit etwas Trifluoressigsäure in Chloroformlösung, (c) und (d) Schütteln einer Ätherlösung mit wässeriger Salzsäure oder Natronlauge. Oxydation von 15A und 15C lieferte eines der Diasteroisomeren von 4,8‐Dimethyl‐spiro[4.5]‐dec‐7‐en‐1,6‐dion (16A), und Oxydation von 15B führte zum anderen (16B).
1,3‐Cyclobutandionderivate aus Keten
Authors: Tenud Leander , Weilenmann Max , Dallwigk Edgar 
Published: December 2004

1,3‐Cyclobutanedione derivatives from keteneThe dimerisation of ketene leads mainly to the methylidene‐β‐lactone ‘Diketene’ 2c. It is shown, that also a small amount of the symmetrical dimer, 1,3‐cyclobutadione 1c is produced, which under the reaction conditions is acetylated to 3‐acetoxycyclo‐butenone (5).
Synthese von Benzofulvenen und Dibenzofulvenen über 1‐Chloralkyl‐acetate
Authors: Neuenschwander Markus , Vögeli Rudolf , Fahrni Hans‐Peter , Lehmann Hans , Ruder Jean‐Pierre 
Published: December 2004

Synthesis of benzofulvenes and dibenzofulvenes via 1‐chloroalkyl‐acetates1,2‐Benzofulvene (6a) and 1,2,3,4‐dibenzofulvene (7a) as well as the corresponding 6‐methyl‐ and 6‐phenyl‐derivatives are prepared by reaction of sodium indenide and sodium fluorenide with 1‐chloroalkyl acetates (3), followed by elimination with KOC(CH3)3. The over‐all yields are comparable with the results of the fulvene series and are in most cases considerably higher than the yields of the Thiele‐method.
Thermische und photochemisch induzierte intramolekulare, 1,3‐dipolare Cycloadditionen von 4‐Phenyl‐3‐(2‐allylphenyl)‐sydnon. Vorläufige Mitteilung. 53. Mitteilung über Photoreaktionen
Authors: Meier Hansruedi , Heimgartner Heinz , Schmid Hans 
Published: December 2004

Thermal and photochemically induced intramolecular 1,3‐dipolar cycloaddition reactions of 4‐phenyl‐3‐(2‐allylphenyl)‐sydnoneThe title compound 9 was synthesised in the usual way, starting from 2‐allylaniline and ethyl 2‐bromo‐2‐phenylacetate, via the nitrosaminacid 8 (Scheme 2). 9 reacts at room temperature with its potential azomethinimine‐function in an intramolecular [3+2]‐cycloaddition to give the tricyclic compound 11 (Scheme 2). On irradiation, 9 yields the dihydro‐3H‐pyrazolo[2,3‐a]indole 10 which probably arises by intramolecular [3+2]‐cycloaddition of the corresponding intermediate nitrilimine.
High‐Pressure, High‐Resolution Nuclear Magnetic Resonance (HPHR‐NMR.): A Tool in Chemical Kinetics
Authors: Merbach André E. , Vanni H. 
Published: December 2004

AbstractIn recent years the volume of activation Δ V* has become a powerful tool in chemical kinetics. High resolution NMR. spectroscopy is now one of the most common techniques used in the study of the kinetics of labile chemical systems. In order to measure Δ V* by this technique, we have built a 1H‐probe‐head, for a Fourier transform spectrometer, working up to 4 kbar and with a resolution of 0.6 Hz. The temperature is regulated and measured with an accuracy better than 0.2°. The high pressure probe‐head has been tested on a chemical system showing a dissociative‐associative crossover for the ligand substitution mechanism. It had been shown previously that the ligand exchange TaBr5 · L + *L ⇄ TaBr5 · *L + L proceeds via a D mechanism when L=Me2O, and via an Ia mechanism when L=Me2S. As expected, ΔV is positive (+30.5 ± 2.0 cm3 mol−1) for the dissociative process and negative (−12.6 ± 1.0 cm3 mol−1) for the associative one.
Synthese von vier chiralen, elektrophilen C3‐ und C4‐Synthesebausteinen aus Hydroxycarbonsäuren
Authors: Seuring Bernhard , Seebach Dieter 
Published: December 2004

Synthesis of four chiral electrophilic C3‐ and C4‐synthons from hydroxycarboxylic acidsThe chiral alkylating reagents4,6c, and10a/bare prepared from lactic, β‐hydroxy butyric, and malic acid, respectively. Their use in natural product synthesis is referred too.
Nucleoside und Nucleotide. Teil 10. Synthese von Thymidylyl‐(3′‐5′) ‐thymidylyl‐(3′‐5′)‐1‐(2′‐desoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyridon
Authors: Cerletti Nico , Tamm Christoph 
Published: December 2004

Nucleosides and Nucleotides. Part 10. Synthesis of Thymidylyl‐(3′‐5′)‐thymidylyl‐(3′‐5′)‐1‐(2′‐deoxy‐β‐D‐ ribofuranosyl)‐2(1 H)‐pyridoneThe synthesis of 5′‐O‐monomethoxytritylthymidylyl‐(3′‐5′)‐thymidylyl‐(3′‐5′)‐1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1H)‐pyridone ((MeOTr)TdpTdp∏d, 5) and of thymidylyl‐(3′‐5′)‐thymidylyl‐(3′‐5′)‐1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1 H)‐pyridone (TdpTdp∏d, 11) by condensing (MeOTr) TdpTd (3) and p∏d(Ac) (4) in the presence of DCC in abs. pyridine is described. Condensation of (MeOTr) TdpTdp (6) with Πd(Ac) (7) did not yield the desired product 5 because compound 6 formed the 3′‐pyrophosphate. The removal of the acetyl‐ and p‐methoxytrityl protecting group was effected by treatment with conc. ammonia solution at room temperature, and acetic acid/pyridine 7 : 3 at 100°, respectively. Enzymatic degradation of the trinucleoside diphosphate 11 with phosphodiesterase I and II yielded Td, pTd and p∏d, Tdp and Πd, respectively, in correct ratios.
An Efficient Approach to Patchouli Alcohol Analogues
Authors: Näf Ferdinand , Decorzant René , Thommen Walter 
Published: December 2004

AbstractA short approach to the tricyclo [5.3.1.03,8] undecane derivatives 1, 10, 11 and 12 and to the tricyclo [4.3.1.03,7] decane derivative 2, starting from industrially available intermediates, is described. Of the compounds 1, 10, 11, and 12, which possess the ring system of patchouli alcohol, 12 also exhibits a woody, patchouli‐like note. The 1H‐NMR.‐spectra of 1, 2 and 8–12 are discussed.
Stereoselektivität und Reaktivität bei der 1,3‐dipolaren Cycloaddition chiraler N‐(Alkoxyalkyl)nitrone
Authors: Vasella Andrea 
Published: December 2004

Stereoselectivity and Reactivity in the 1,3‐Dipolar Cycloaddition of Chiral N‐(Alkoxyalkyl)nitronesThe stereoselectivity in the reaction of hydroxy‐oxime 1 with acetaldehyde and methyl methacrylate yielding the diastereomeric isoxazolidine‐ribosides 9–12 was determined to be 93%. The predominant adducts 9 and 10 were cleaved to the diastereomeric isoxazolidines 19 and 20, respectively, which upon oxidation gave the same optically active 2‐isoxazoline 21, thus demonstrating the participation in the cycloaddition of both (E/Z)‐isomeric nitrones 13 and 14. Based upon comparison of the optical rotations, the isoxazolidines 7, 8, 19 and 20 and the 2‐isoxazolines 21 and 22 possess the same chirality, found to be R by correlating 7 with (+)‐(S)‐citramalic acid. ‐ Since the hydroxy‐oximes 1 and 36 showed the same stereo‐selectivity in the reaction with formaldehyde and methyl methacrylate, the trityl group of 1 does not influence the stereoselectivity in the cycloaddition. The hydroxyoxime 38 led in the same type of reaction to the isoxazolidines 7, 8, 19 and 20 possessing (S)‐chirality, the stereoselectivity (79–95%) being similar to the one observed with 1 (67–95%). The explanation of this stereoselectivity is based upon a stereoelectronic effect in the transition state of the cycloadditions (kinetic anomeric effect). As predicted, the N‐(alkoxyalkyl)nitrones showed enhanced reactivity in the cycloaddition with unactivated olefins (leading to 47, 48, 50 and 51). The importance of exo vs. endo approach of the dipolarophile was evidenced by reacting 1 with formaldehyde and methyl acrylate giving predominantly 57 with (5S)‐configuration. ‐ Use of the hydroxy‐oxime 65 allows synthesis of optically active isoxazolidines with regeneration of the starting hydroxy‐oxime.
Diénamines hétérocycliques. III. Réexamen de la réaction de la base de Fischer avec le tétracyanoéthylène
Authors: Hubschwerlen Christian , Fleury Jean‐Pierre , Fritz Hans 
Published: December 2004

Heterocyclic dienamines III. A re‐examination of the reaction of Fischer's base on tetracyanoethyleneDepending on the order of addition, Fischer's base 5 (1,3,3‐trimethyl‐2‐methylidene‐indoline) reacts 1:1 with tetracyanoethylene to give either the tricyanovinylation product 6 or the spiro compound 7. A skeletal rearrangement of a zwitterionic intermediate can explain the formation of the spiro compound. The latter undergoes a thermal isomerization yielding by ring expansion the tetrahydroquinoléine 8. On reaction with LiAlH4 or CH3ONa 7 and 8 lead both to triazatetracycles. All structures are assigned on the basis of spectral data.
Note sur quelques complexes entre nicéthamide (N,N‐diéthyl‐nicotamide) et/ou de la pémoline (phényl‐5‐imino‐2‐oxazolidone‐4) et divers sels, particulièrement de sels calciques de monoesters aminoalkylphosphoriques
Authors: Rabinowitz J. , Thorndahl S. , Gold‐Aubert Ph. 
Published: December 2004

Note on some complexes between nikethamide and/or pemoline with various salts, especially calcium aminoalkylphosphatesA number of binary and ternary complexes of nikethamide and/or pemoline with various calcium salts, particularly calcium aminoalkylphosphates, have been prepared in order to assess their pharmacological properties. The formation of such complexes has been established by IR. spectroscopy.
Zum basenkatalysierten H/D‐Austausch des acetylenischen Wasserstoffatoms in aromatischen Alkinylverbindungen
Authors: Kramis Jost , Hansen Hans‐Jürgen 
Published: December 2004

On the Base‐Catalysed H/D‐Exchange of the Acetylenic Hydrogen Atom in Aromatic Alkynyl CompoundsH/D‐exchange rates for a number of compounds of the general type 1 (X = p‐CH3O, m‐CH3O, p‐CF3, m‐CF3, p‐CH3, p‐Cl, H; Z  O, NH, CH2) were determined in N‐methyl‐pyrrolidine (NMP)/D2O mixtures at 25° (see Table 1).It is shown that the log k values of the H/D‐exchange correlate nicely (r = 0.995) with the chemical shift of the acetylenic proton in 1. Thus, the H/D‐exchange rate is given by log k (min−1) = 2.91 · δ (ppm) ‐ 7.79 for the NMP/D2O mixture at 25°.
Neue 18‐substituierte Steroide. I. 18‐Methylidenprogesteron über Steroide 232. Mitteilung
Authors: Kalvoda Jaroslav , Grob Jürgen , Anner Georg 
Published: December 2004

New 18‐Substituted Steroids. I. 18‐MethylideneprogesteroneThree independent syntheses of 18‐methylideneprogesterone, the first representative of a new group of biologically highly active steroidal compounds, are described. In the first approach 3‐acetoxy‐20‐oxo‐5‐pregnen‐18‐carbonitril (2) is transformed into the final product by a reaction sequence involving the Cope degradation of the N‐oxide 6 of the corresponding tertiary aminomethyl derivative. The Wittig reaction 3,3,20,20‐Bis(äthylendioxy)‐5‐pregnen‐18‐al (11) represents the crucial step in the second synthesis. In the last procedure the 18‐methylidene‐20‐oxo grouping is generated by fragmentation of an 18,21‐bridged 1,3‐diol system (19). The two former methods are very versatile and generally applicable for the synthesis of other analogues.
Ringschlussreaktionen mit 2‐(β‐Styryl)benzylaminen 5‐Phenyl‐1H‐2‐benzazepine. 23. Mitteilung über siebengliedrige Heterocyclen
Authors: Gast Gérard , Schmutz Jean , Sorg Dieter 
Published: December 2004

Cyclization reactions with 2‐(β‐styryl)benzylamines 5‐Phenyl‐1H‐2‐benzazepinesCyclization of the urea derivative 3 with POCl3 to give 2‐(4‐methyl‐1‐piperazinyl)‐4‐phenylquinoline (4) was carried out in analogy to the quinoline synthesis of Foulds & Robinson. This reaction was used for the preparation of 2‐benzazepines. The trisubstituted ureas 6 and 8, derived from the 2‐(β‐styryl)‐benzylamines 5, were cyclized with POCl3 to yield the 3‐amino‐5‐phenyl‐1H‐2‐benzazepines 7 and 9, respectively. Similarly, cyclization of the corresponding acetyl‐derivatives 10 gave the 3‐methyl‐5‐phenyl‐1H‐2‐benzazepines 12. On the other hand, the disubstituted urea 15, cyclized under the same conditions to the 1‐methyl‐1‐phenylisoindoline derivative 16, and 2‐(β‐styryl)benzylamine (5a) on treatment with phosgene gave the isoindoline 17 in an analogous manner.
Solvolytic Ring‐opening of Alkoxychlorofluorocyclopropanes: A Ready Access to Fluorinated α,β‐Unsaturated Aldehydes and Ketones
Authors: Bessière Yvonne , Savary Dang Ngoc‐Huê , Schlosser Manfred 
Published: December 2004

AbstractAlkoxychlorofluorocyclopropanes are easily prepared by chlorofluorocarbene addition to en‐ethers in a two‐phase system and converted by simple heating in an aqueous solvent mixture to 2‐fluoro‐2‐alkenals which can be reduced to the corresponding alcohols.
Zur Biogenese des Muscarins in Mycelkulturen von Clitocybe rivulosa
Authors: Nitta Keiichi , Stadelmann René Josef , Eugster Conrad Hans 
Published: December 2004

Studies on the biosynthesis of muscarine in mycelial cultures of Clitocybe rivulosaThe incorporation and distribution of several 14C‐labelled simple compounds into muscarine has been investigated with mycelial cultures of Clitocybe rivulosa. Specifically, the carbon atoms 1, 2 and 3 of pyruvate are incorporated into CH3‐C(2), C(2) and C(3), and the carbon atoms 2, 3 and 4 of glutamate into C(4), C(5) and CH2‐C(5) of muscarine. The carbon atoms 1 and 5 of glutamate are lost during the biosynthesis. Therefore, muscarine can be regarded as a derivative of glutamate.
Zur Kenntnis des Aminal‐Enamin‐Gleichgewichtes bei Cyclopropan‐carbaminalen
Authors: Huber Martin K. , Martin Roger , Rey Max , Dreiding André S. 
Published: December 2004

The Aminal‐enamine Equilibrium in Cyclopropane‐carbaminals.The following cyclopropane‐carbaminals were synthesized: N,N′‐(T‐2,t‐3‐dimethyl‐r‐1‐cyclopropyl)methylene‐dipyrrolidin (15), the corresponding (c‐2, c‐3)‐isomer 16, N,N′‐(cyclopropyl)methylene‐dipyrrolidin (17) and N,N′‐(c‐2, t‐3‐diphenyl‐r‐1‐cyclopropyl)methylene‐dipyrrolidin (18). Their constitutions and configurations were derived from the method of synthesis and from 1H‐NMR.‐spectra. The c‐c‐r‐1‐dimethyl‐aminal 16 rearranged at room temperature to its t‐t‐r‐1‐dimethyl‐isomer 15. This demonstrates the existance of an aminal‐enamine equilibrium for cyclopropane‐carbaminals although cyclopropane‐carbenamines have not been isolated as yet. The kinetic data found for the rearrangement of 16 to 15 are compatible with two mechanisms: In the first one, the protonated aminal 21 decomposes into the iminium‐ion 22, which, in turn, yields the enamine 19. In the second one, 21 is converted to 19 in a single step. The formation of cyclopropyl‐pyrrolidino‐acetonitrile (26) and dipyrrolidino‐ethylene‐1,1‐dicarbonitrile (27) from the reaction of the aminal 17 with tetracyanoethylene may also be explained with an aminal‐enamine equilibrium. ‐ This equilibrium lies strongly on the side of the aminal. Investigations of the aminal‐enamine ratio of several cycloalkanecarbaminals, namely of the 3‐ring derivative 17, the 4‐ring derivative 35 and the bicyclic 5‐ring derivative 38, show that ring strain is a determining factor for the equilibrium bias. This strain may also explain that the aminomethanol 41 was isolable.Some of the aminals were synthesized from previously unknown aldehydes. t‐2, t‐3‐dimethyl‐r‐1‐cyclopropane‐carbaldehyde (11) and its (c‐2, c‐3)‐isomer 12 were obtained by stereoselective ring‐contraction of the 2‐chloro‐cyclobutanols 46 and 48/49, respectively. The configurations of the aldehydes 11 and 12, of the starting cyclobutanones 44 and 45 and of the cyclobutanol 46 were established by 1H‐NMR. measurements. From the steric course of the ring contraction it can be concluded that it is the fastest rearrangement of 2‐halo‐cyclobutanols with base, when the conformation having an equatorial halogen atom is not obstructed. c‐2, t‐3‐diphenyl‐r‐1‐cyclopropane‐carbaldehyde (14) and 3‐phenyl‐1‐cyclobutane‐car‐baldehyde (34) were synthesized by reduction of the corresponding ester 50 and acid 52, respectively, followed by Sarett‐oxidation.
Umlagerung von Vinyl‐Cyclopropan‐Carbaminalen
Authors: Huber Martin K. , Martin Roger , Dreiding André S. 
Published: December 2004

Rearrangement of Vinyl‐Cyclopropane‐CarbaminalsBoth (c‐2, t‐3‐diphenyl‐r‐1‐cyclopropyl)methylene‐dipyrrolidine (4) and its (t‐2, t‐3)‐isomer 10 underwent a thermal rearrangement to (E)‐N‐2‐benzylidene‐1‐indanyl‐pyrrolidine (5). Under the conditions of the rearrangement, 5 was partially converted into 2‐benzyl‐1‐indanone (6) in a base catalysed reaction. The structures of 5 and 6 were derived from spectroscopic data and from degradation reactions.‐ N,N′‐(t‐2‐Vinyl‐r‐1‐cyclopropyl)methylene‐dipyrrolidine (11) rearranged thermally to N‐(2‐methylidene‐3‐cyclopenten‐1‐yl)pyrrolidine (12), the structure of which was established from spectroscopic evidence and from a hydrogenation to N‐(2‐methylcyclopentyl)pyrrolidine (13, cis/trans mixture 3:2).The aminal 4 was reduced with formic acid to give N‐(c‐2, t‐3‐diphenyl‐r‐1‐cyclopropyl)methyl‐pyrrolidine (14). If perdeuterio formic acid was used, the mixture product 14‐d/14‐d2 was obtained which contained exactly one deuterium atom in its methylene group and about half a deuterium atom on C(1). This labeling pattern is mechanistically explained with the existence of a fast equilibrium between the iminium ion 19 and the enamine 18, so that 18 and 19 are considered to be plausible reactive intermediates in the above mentioned thermal rearrangement. ‐ Based on this, several mechanisms for the rearrangements 4 → 5, 10 → 5 and 11 → 12 were considered: A Pictet‐Spengler‐ or Mannich‐type reaction, which starts from the iminium ion 23 and is followed by a cyclopropylmethyl‐homoallylic rearrangement and by deprotonation (path a, Scheme 5), was judged to be improbable because the postulated intermediates could lead more easily to other stable products than the observed ones. If the reaction is formulated as a [3,3]‐sigmatropic shift occurring on exclusively the (E)‐isomer 5 suggests a concerted process whose steric course is predominantly controlled by strain factors. Alternatively, the reaction could be formulated via a dipolar (27) or a diradical (26) species derived from the enamine 22 (paths c and d, Scheme 5); attempts to trap such species by a number of agents were unsuccessful. ‐ The previously unknown aminals 10 and 11 were synthesized by standard methods.
MO‐Calculation of the Optical Activity of Oligopeptides. I. Computational Procedure and Application to Small Helices
Authors: Wagnière Georges , Iseli Max , Geiger Rudolf , Gans Werner 
Published: December 2004

AbstractAll‐valence electron calculations on the chiroptic properties of oligopeptides rapidly become intractable, as the size of the molecule increases. A Frozen Core procedure is here proposed, which is inspired by the PPP method. It takes explicitly into account only the (pseudo) π electrons and oxygen n electrons of the amide moieties, as well as the π electrons of eventual long‐wavelength absorbing sidegroups. Local n‐π interaction is taken into account by an adjustable parameter. Other parameters are calibrated on the isolated amide and carbonyl chromophores. The method then follows the usual SCF‐CI procedure. Rotatory strengths and f‐values for the transitions are computed without further approximations, as previously described. Comparisons with results from exciton calculations and experimental data on polypeptides show the computed quantities to have a consistent and satisfactory order of magnitude.
Proximity Effects in Acid and Base‐Catalysed Ether Formation
Authors: Grob Cyril A. , Katayama Hajime 
Published: December 2004

AbstractWhen heated with sodium ethoxide in ethanol 7‐methylidenebicyclo[3.3.1]nonan‐3‐endo‐ol (endo‐1) is converted into 1‐methyl‐2‐oxa‐adamantane (3). This reaction involves nucleophilic addition of a hydroxy group to an unactivated olefinic bond. Formation of the cyclic ether 3 also takes place when endo‐1 is heated in aqueous ethanol. This electrophilic addition is strongly catalysed by weak acids and suppressed by weak bases. These unusual reactions proceed more slowly with 7‐methylbicyclo[3.3.1]non‐6‐en‐3‐endo‐ol (endo‐2) and can be ascribed to a proximity effect. This follows from the IR. and NMR. spectra of endo‐1 and endo‐2 which show strong intramolecular hydrogen (OH‐π) bonding. The unsaturated endo‐ and exo‐alcohols 1 and 2, respectively, undergo only exo‐complexation with silver ion.
π‐Spin distribution in the radical anion of benzo[2.2]paracyclophane and its relation to those in the radical anions of [2.2](1,4)naphthalenophanes
Authors: Bruhin Jürg , Gerson Fabian , Martin William B. , Wydler Christoph 
Published: December 2004

AbstractRadical anions of benzo[2.2]paracyclophane (V) and its 1,2,12,12,14,15,17,18‐octadeuterio derivative (V‐d8) in three ethereal solvents (DME, THF and MTHF) and in the temperature range of −90 to −50° have been studied by ESR. and ENDOR. spectroscopy. The resulting hyperfine data provide a detailed picture of the π‐spin distribution in V · ⊖ which is in full accord with expectation. In particular, it is noteworthy that the naphthalene moiety accommodates almost the entire π‐spin population, as may be anticipated by the higher electron affinity of this π‐system relative to benzene. The proton coupling constants for V · ⊖ have been compared with those values for the radical anions of anti‐ and syn‐[2.2](1,4)‐naphthalenophanes (II and III, respectively) which were obtained under conditions of low frequency electron transfer between the two equivalent naphthalene moieties. Such a comparison corroborates the interpretation of the results reported previously for II · ⊖ and III · ⊖.