摘要:

AbstractThe N(α), N(β)‐rearrangement of the two N‐atoms which can be observed in solutions of [β‐15N]‐labelledp‐substituted benzenediazonium ions follows dual substituent parameter treatments. The reaction yields a negative field and a positive resonance reaction constant (pF=−3.35,pR= 2.47). The magnitude of these constants is, within experimental error, the same as the respective reaction constants for solvolytic dediazoniation. The exchange of the diazonio group of15N‐labelledp‐substituted benzenediazonium ion yields, however, field and resonance reaction constants which are close to zero. This result is attributed to cancellation of the reaction constants for the forward and reverse steps in the complex mechanism of the

ISSN:0018-019X    

DOI:10.1002/hlca.19880710302

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe N2‐molecule‐aryl‐cation pair formed as the first intermediate in dediazoniations of arenediazonium ions can be trapped with CO in H2O with formation of the corresponding arenecarboxylic acids. This reaction is considered as a model for the reverse of dediazoniation, since CO is isoelectronic with N2. The evaluation of the yields of arenecarboxylic acids formed from substituted benzenediazonium ions usingTaft's dual substituent parameter treatment demonstrates that the field reaction constantpFand the resonance reaction constantpRare positive and negative, respectively, as expected for a reaction which corresponds electronically to the addition of N2to aryl ca

ISSN:0018-019X    

DOI:10.1002/hlca.19880710303

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

15N‐Labelled 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirine for Mechanistic Studies of Reactions with NH‐Acidic HeterocyclesThe synthesis of 3‐(dimethylamino)‐2,2‐dimethyl(1‐15N)‐2H‐azirine (1*) was accomplishedviareaction of 1‐chloro‐N,N,2‐trimethyl‐1‐propenylamine (9) and sodium (1‐15N) azide (Scheme 3). The earlier reported reactions of1with saccharin (10,Scheme 4), phthalimide (12,Scheme 5), and2H‐1,3‐benzoxazin‐2,4(3H)‐dione (16,Scheme 6) were repeated with1*, and the position of the15N‐label in the products was determined by15N‐NMR spectroscopy. Whereas the postulated reaction mechanisms for10and12were confirmed by these experiments, the mechanism for the reaction of16had to be revised. With respect to the position of15N in the products17and18, a new mechanism is formulated inScheme 7. Treatment of 5,5‐dimethyl‐1,3‐oxazolidine‐2,4‐dione (19) with1* led to 3,4‐dihydro‐2H‐imidazol‐2‐on20in which only N(3) was labelled. The mechanism of a ring expansion and transannular

ISSN:0018-019X    

DOI:10.1002/hlca.19880710304

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractA new synthesis of deoxysepiapterin (2), one of the two yellow eye pigments of theDrosophilamutantsepia, is described. The synthetic approach makes use of a homolytic nucleophilic acylation of 7‐(alkylthio)pteridine derivatives (11, 13, 15, 18, 20) leading to the corresponding 6‐acyl derivatives (21–27). Desulfurizations have been achieved for the first time in the pteridine series usingRaney‐Co,Raney‐Cu, or CuAl alloy in alkaline medium. Besides cleavage of the C(7)S bond, further reductions of the CO group at C(6) and the C(7)N(8) bond are detected as side reactions leading to 6‐(1‐hydroxyalkyl) (34, 35, 42, 43) and 6‐acyl‐7,8‐dihydro derivatives (2, 36, 37), respectively, The newly synthesized compounds have been characterized by elemental analysis, pKdetermin

ISSN:0018-019X    

DOI:10.1002/hlca.19880710305

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe stereochemistry of theDiels‐Alderreaction of 1,2‐dichloro‐3,3‐difluorocyclopropene (5a) to 1,4‐diphenyl‐1,3‐butadiene (6) and 1,3‐diphenylisobenzofuran (7) was unambiguously established by X‐ray structure determination. In all cases known so far, tetrahalogenocyclopropenes addexoto open‐chain dienes and furans. The previously reportedexo‐addition product (2a) of l‐bromo‐2‐chlorocyclopropene (5b) to7allows assignments of the stereochemistry of other additions of5bto furans.exo‐Addition usually predominates, but in some casesendo‐ adducts are also formed. This contrasts with reports in the literature that5badds prefere

ISSN:0018-019X    

DOI:10.1002/hlca.19880710306

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractOn irradiation in the presence of Fe(CO)5, the allenecarboxylates1afforded binuclear carbonyliron complexex6(Scheme 3), whereas the allenic lactone 7 under similar conditions gave a mixture of one binuclear and two mononuclear carbonyliron complexes (9,8, and10;Scheme 4). The structure of the complexes has been elucidated by X‐ray crystallography. The structure of the binuclear complex9corresponds to that of6, while8has been shown to be a 1,3‐butadiene(tricabonyl)iron complex. The unique structure of the10represents a new type of allenic complex. A stepwise formation of the complexesviaintermediate allene(tetracarbonyl) iron complexes type11and13is suggested. Treatment of the binuclear complex6bwith FeCl3led to the formation of the free ligand and a mixture of mononuclear complexes13and14(Scheme 5). On heating, the 1,3‐diene complex8yielded the free ligand15, the prouduct of a (1,3) H shift in the allene7; the complex10on the other hand liberates 7 on treatment with ethylenetracarbonitrile (TCNE)(Sche

ISSN:0018-019X    

DOI:10.1002/hlca.19880710307

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe hexadentate ligands 1,4,7,12,15,18‐hexaazacyclododecosane ([2]aneN6) and 1,4,7,14,17,20‐hexaazacyclohexacosane ([26]aneN6) both form eight complexes with Cu2+, three of them being binuclear. The corresponding stability constants have been determined potentiometrically, and the electronic absorption spectra have been obtained from spectrophotometric data. Possible interactions of the Cu2+pairs in the three binuclear complexes have, in addition, been investigated by ESR and and linear ‐sweep voltammetry (LSV). The binuclear complex of [22]aneN6with one addditional OH group is exceptionally stable, ESR‐silent, and the results of the LSV‐experiments are characteristically different from those of the other binuclear complexes with both ligands. This indicates that [22]aneN6forms a very stable hydroxo‐bridged binuclear Cu2+complex Cu2L(OH)3+, whereas in the case of [26]andN6no bridged Cu2+

ISSN:0018-019X    

DOI:10.1002/hlca.19880710308

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe angular triquinane (−)‐silphiperfol‐6‐en‐5‐on ((−)‐14) has been synthesized for the first time time in enantiomerically pure form. A highly efficient triplet‐sensitized photoreaction, the oxadi‐π‐methane rearrangement of the complex β,γ‐enone(+)‐6to (−)‐7, constitutes the key step. The know staring material, (1R, 7aR)‐3,6,7,7a‐tetrahydro‐1‐hydroxy‐7a‐methyl‐1H‐inden‐5(2H)‐one ((−)‐2), is readily accessible in>97% enantiomeric purity. This new approach should enable access also to other angularly fused t

ISSN:0018-019X    

DOI:10.1002/hlca.19880710309

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

Fredericon A, B, C, and D, Novel and Highly Functionalized Abietanoids from Leaf‐Glands ofColeus fredericiiFrom the leaf‐glands of the title plant (fam. Labiatae) two novel, genuie spirocycloopropyl‐coleons have been isolated and structurally characterized. Fredericon A (1) bears the unusal 1,1,2‐tricarbonylcyclopropane substructure that renders the molecule very suseptible to nucleophile‐promoted rearrangements. Biogenetically intriguing is the presence of a 3‐acetoxypropyl side‐chain in fredericon B (3). Its formation from the well known isopropyl group is explained by transformation of the latter into a spirocyclopropane, followed by a reductive opening of the cyclopropane and reducation of the aldehyde, MeOH addition to1, yields fredericon C (5), a derivative of 1H‐phenanthro[3,2‐b]pyran‐7,12(2H,8H)‐dione by two consecutive introlecular nucleophilic openings of the cyclopropane ring and the derived methoxy‐oxirane. Similar methanolysis of a crude fraction of1, produced, in addition to5, the fredericon D, a novel derivative of 3H‐phenanthro[

ISSN:0018-019X    

DOI:10.1002/hlca.19880710310

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractSambucinic acid (5), a C15‐trichothecene with a modified strure, has been isolated from cultures ofFusarium sambucinum. The structure is established by spectroscopic data and X‐ray diffraction analysis. A hypothetical biogenetic pathway is propo

ISSN:0018-019X    

DOI:10.1002/hlca.19880710311

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY