摘要:

Abstract(−)‐(S)‐2‐Hydroxy‐β‐ionone (33), (+)‐(2S, 6S)‐2‐hydroxy‐α‐ionone (34), and their acetates35and36have been synthesized from (+)‐(S)‐6‐methylbicyclo [4.3.0]‐non‐1‐ene‐3, 7‐dione (3). The key intermediate (+)‐(1R, 3S, 6S)‐2, 2, 6‐trimethyl‐7‐oxobicyclo [4.3.0]non‐3‐yl acetate (7) was correlated with a degradation product of the pentacyclic triterpene ursolic acid (16). Compound33was also synthesized by an al

ISSN:0018-019X    

DOI:10.1002/hlca.19810640402

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

WittigReactions of Phosphoniomethylaryl Compounds with Sulfonated Aromatic and Heteroaromatic AldehydesBis (triphenylphosphoniomethyl)aryl dichloride derivatives react with aromatic or heteroaromatic aldehydes which have a sulfonic or carboxylic group attached to the ring system, to yield stilbene compounds of a betaine‐type structure. These betaines are reacted further with various aromatic or heteroaromatic aldehydes yielding asymmetrically substituted derivatives in excellent yields. This new method is widely applicable to the preparation of water‐soluble, fluorescent whitening agents of the bis‐stilbene

ISSN:0018-019X    

DOI:10.1002/hlca.19810640403

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractConformational effects on the one‐bond Cα, H coupling constant have been studied in cyclic oligopeptides containing glycine, alanine, sarcosine and proline. The conformational contribution to1J(Cα, H) can be described as being composed of apositivehyperconjugative term from the neighbouring N‐pzorbital and anegativeone from the carbonyl π‐system. For glycyl units, a quantitative relation between1J(Cα,H) and the vicinal interorbital angles Φ′ and Ψ′ is derived with maximum values ΔJ(Ψ′) = + 14.0 Hz and ΔJ(Ψ′) = −4.9 Hz. Applications to conformational analysis of cyclo (L‐Pro‐Gly)3, cyclo (D‐Ala‐D‐Ala‐L‐Ala‐D‐Ala

ISSN:0018-019X    

DOI:10.1002/hlca.19810640404

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractPhotodecomposition of dimethylnitrosamine in the gas phase ( ∼ 1 Torr) has been investigated following irradiation into the S1(nπ*) ← S0(363.5 nm) and S2(ππ*) ← S0(248.1 nm) transitions at room temperature. With a quantum yield of unity, excitation into the S1state yields the fragments (CH3)2N⋅ and NO which then recombine leaving no photoproducts. The addition of O2results in only one photoproduct, (CH3)2NNO2. Irradiating into the S2state, the products CH2NCH3, (CH2NCH3)3, CH2NOH, N2O, NO, H2, and N2were identified by capillary gas chromatography mass spectrometry. In the presence of N2as a buffer gas the photoproducts are only CH2NCH3, (CH2NCH3)3, N2O, and H2. For both excitation conditions a mechanism is proposed involving cleavage of the N, N‐bond as the m

ISSN:0018-019X    

DOI:10.1002/hlca.19810640405

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Heterodiamantanes and Structurally Related Compounds. Part III. The Pentacyclic C11‐Diethers 5, 13‐Dioxapentacyclo [6.5.0.02,6.03,12.04,9]tridecane, 4, 13‐Dioxapentacyclo [6.4.1.02,7.03,10.05,9]tridecane, and 3, 10‐Dioxapentacyclo [7.3.1.02,7.04,12.06,11]tridecaneIn connection with the studies on heterodiamantanes and structurally related compounds the three novel pentacyclic diethers3–5were prepared starting from the cyclopentadienone dimer6. All four compounds have as common features a central carbocyclic 6‐membered ring with four axial alkyl substituents and two oxygen functions in 1, 4 position. The required eleventh C‐atom was introduced by dichlorocarbene addition either to6( →7)(Scheme 2)or to29( →28)(Scheme 4).Diether3was obtained by reduction of26(Scheme 2), a suitable precursor prepared either by intramolecular addition (24→26;Scheme 2) or substitution (30→26,31→26;Scheme 4), as well as by direct substitution (44→3,42→3;Scheme 5). Diether4was the product of a direct substitution (39→4,36→4;Scheme 5). The synthesis of diether5was achieved from the addition product51(resulting from the alcohols47and48;Scheme 6).Diether4is the thermodynamically least stable of the three diethers3–5. It was easily isomerized to5on treatment with concentrated sulfuric acid in benzene whereas3and5remained

ISSN:0018-019X    

DOI:10.1002/hlca.19810640406

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractDeprotonation of ethyl (E)‐2‐alkenoates1,3and4yields after protonation the double bond migrated (3Z)‐isomers5,7and9as major products. In contrast, deprotonation and reprotonation of ethyl (Z)‐2‐pentenoate (2) gives the (3E)‐isomer6exclusively. These findings are explained by reaction paths starting from different ester co

ISSN:0018-019X    

DOI:10.1002/hlca.19810640407

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

A New Route to 1, 3‐Dicarbonyl Derivatives, Model Investigations on the A/B‐Part of‐3‐Oxo‐5α‐steroidsStarting from1the 1, 3‐dicarbonyl compounds4a–dwere synthetizedviathe enynes2a–eand the relatively unstable epoxides3a–d. The latter were reacted with 95% formic acid to gave4a–d; small amounts of the furane derivatives5a–cwere identified as by‐products in this last step. In the presence of catalytic amounts of HgSO4the epoxides3a–cyielded with 95% formic acid the furanes5a–c, bu

ISSN:0018-019X    

DOI:10.1002/hlca.19810640408

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractIt was found that analysis of the1H‐NMR. signals (at 360 (preferably) and/or 100 MHz) of the protons at C (4) and of the equatorial α‐proton at C (6), particularly when these are located in the 2–3 ppm region and therefore convenient for detection and identification, may be of valuable aid in the structural and configurational characterization of 5‐hydroxy‐ and 5‐acetoxy‐steroids (unsubstituted or containing a hydroxy or acyloxy substit

ISSN:0018-019X    

DOI:10.1002/hlca.19810640409

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Spherical Cryptates. Synthesis and Inclusion‐Complexes of Spherical Macrotricyclic LigandsA general strategy for the synthesis of spherical macrotricyclic ligands has been developed. Four spherical cryptands,SC‐24,SC‐25,SC‐26andSC‐27have been obtained by this route. The synthesis and cation‐complexing properties of these compounds are described in detail. Stability constants and cation exchange rates of the spherical cryptates obtained with alkali and alkaline‐earth cations have been determined. Highly stable complexes are formed bySC‐24; the Rb+and Cs+cryptates ofSC‐24are the most stable complexes of these cations known to date. The size of the intramolecular cavity affects the complexation selectivity. The cation exchange rates are very slow, and the corresponding free energies of activation are even larger than, for macrobicyclic cryptates of similar stability. Both the high complex stabilities and the high activation energies required for cation exchange indicate a marked ‘spherical cryptate effect’ resulting from the highly connected nature of the molecular architecture of spherical m

ISSN:0018-019X    

DOI:10.1002/hlca.19810640410

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractThe rates of proton transfer from 2, 4‐hexadiene, 1, 3‐cycloheptadiene, cyclopentadiene and acetone tot‐butoxide have been measured in the gas phase using pulsed‐ion‐cyclotron‐resonance spectroscopy. The rate constants are (units of 10−10cm3molecule−1s−1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile fort‐butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central bar

ISSN:0018-019X    

DOI:10.1002/hlca.19810640411

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY