摘要:

Synthesis of ‘Push‐Pull’ DiacetylenesThe first synthesis of push‐pull diacetylenes of type1is described. Reaction of perchlorobutenyne (8) with two equivalents of dialkylamine, followed by dechlorination using two equivalents of butyllithium gives lithio‐dialkylamino‐diynes7. Final acylation of these intermediates leads to push‐pull diacetylenes1b–1ein good yields. The method allows the introduction of both push and pull substituents in a simple one‐pot‐procedure. In addition,1ais prepared by hydroxymethylation of lithio‐morpholino‐diyne7c, followed by oxidation with manga

ISSN:0018-019X    

DOI:10.1002/hlca.19830660602

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractOn singlet excitation (λ=254 nm, acetonitrile) the diepoxydiene (E)‐7undergoes photocleavage to the carbonyl ylideVIIand the carbenesXandXI. The carbonyl ylideVIIrearranges to the thermally labile dioxabicyclo [3.2.1]octene20or fragmentsviaVIIIto the aldehyde9and propyne. The carbeneX, showing behaviour typical of vinyl carbenes, undergoes addition to the adjacent double bond furnishing the cyclopropene11. The carbeneXI, however, undergoes an insertion reaction into the neighbouring oxirane C,C‐bond leading to the oxetene (E)‐21which can be isolated at −78°, but at room temperature is rapidly transformed to the aldehyde10. On triplet excitation (acetone, λ>280 nm), however, (E)‐7shows the typical behaviour of epoxydienes, undergoing C, O‐cleavage of the oxirane and isomerization to22,

ISSN:0018-019X    

DOI:10.1002/hlca.19830660603

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe stereochemical course of the intramolecular allylsilane‐aldehyde condensation of1ahas been investigated. A modest preference for the product arising from a synclinal orientation of double bonds was observed withLewis‐acid catalysts. Cyclization induced by fluoride ion resulted in stereochemical rever

ISSN:0018-019X    

DOI:10.1002/hlca.19830660604

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe31P{1H}‐NMR characteristics of the complexes [HgX2(1)] and [HgX2‐(PPh2Bz)2] (X = NO3, Cl, Br, I, SCN, CN) and the solid state structures of the complexes [HgCl2(1)] and [HgI2(1)] (1= 2,11‐bis (diphenylphosphinomethyl)benzo‐[c]phenanthrene) have been determined.The1J(199Hg,31P) values increase in the order CN

ISSN:0018-019X    

DOI:10.1002/hlca.19830660605

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe structure of a colorless dimer (4a) of puupehenone (1), which was isolated from Pacific marine sponges, has been elucidated from spectral data.

ISSN:0018-019X    

DOI:10.1002/hlca.19830660606

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractLigand substitution reactions on square‐planar platinum (II) complexes of the typestrans‐[PtRXL2],trans‐[PtR(4‐PADA)L2][BF4],trans‐[PtRX() andtrans‐[PtR(4‐PADA)()][BF4] R=H, Me; X=Cl−, I−; L=PEt3, bis(3‐trifluoromethyl‐phenyl)benzylphosphine (4),=thetrans‐spanning 2,11‐bis[bis(3‐trifluoro‐methylphenyl)phosphinomethyl]benzo [c]phenanthrene (3); 4‐PADA (=pyridine‐4‐azo‐4′‐(N,N‐dimethyl)aniline have been studied at 30° using stopped‐flow and conventional spectrophotometry, methanol as solvent, and 2.5 × 10−2Mionic strength (LiClO4as supporting electrolyte). 4‐PADA was used as indicator ligand, as its absorption spectrum differs from those spectra where it is complexed.The expected steric effects of the bulky ligands, especially of3, on the rates and mechanisms of all the reactions studied are small. All reactions take place by the usual two‐term rate law. Noteworthy, for the complexes with the bulky ligands3and4, the direct reaction path with the entering nucleophile is predominant. There is no preference for a solvent or dissociative path. The reactivity order for the hydride complexes istrans‐[PtHX (PEt3)2]

ISSN:0018-019X    

DOI:10.1002/hlca.19830660607

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractReactions of the title compound1with various nucleophiles have been studied. The salt behaves like an alkylating agent towards ethers, alcohols and water forming ethyl diazoacetate (2), which reacts further with excess of the nucleophile. A solvent cage mechanism accounting for the observed products is proposed. Thermal decomposition in inert solvents leads to the alkylation of the counter‐ion,i.e.formation of chloroethane, and in anisole, alkylation and chlorination of the solvent are also observed.With a standard coupling component, 2‐naphtholate ion, no azo coupling reaction of1is observed, but instead 14‐methyl‐14H‐dibenzo[a,j]xanthene (17) is formed. The products of the reaction with diethylamine are diethylcyanoformamide (18) and ethyl diethylcarbamate (19). None of the chemistry of salt1is explained by the intervention of vinyl cations expected to be formed in a heteroytic dediazoniation. The predominant pathways seem to involve reactions of an oxonium salt (alkylating properties) or, in the case of diethylamine, a carbenium salt (primary nucleophilic attack on the β‐C‐atom of1).The free energy barrier to CC rotation in1is estimated to be 75 to 77 kJ/mol (18.0 to 18.5 kcal/mol), a value which falls between those expected for a double a

ISSN:0018-019X    

DOI:10.1002/hlca.19830660608

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe title compound (1) reacts with excess methanol forming a rearranged product, 9‐methoxyphenanthrene (2). 9‐(Methoxymethylidene)fluorene (4) does not rearrange to give2under the same conditions. In deuterated methanol no labelled product is obtained, showing that the possible mechanism involves either the formation of a primary vinyl cation5rearranging to an aryl cation6or the formation of a β‐alkoxycarbene (12), which rearranges to an arene. The results obtained are compared with previously reported reactions, which were postulated to proceedviaa 2,2(2′,2″‐biphenylylene)ethene‐1‐di

ISSN:0018-019X    

DOI:10.1002/hlca.19830660609

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractNew substrates and reaction conditions which may be expected to yield phenyl cation intermediates have been investigated. The approaches used were: (a) solvolysis of PhX in fluorinated alcohols, where X = N (O) = NOTs (tosyloxyazoxy), N (O) = NONf (Nf = C4F9SO 2−) and OSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document}(CH3)3ŌTf (Tf=CF3SO 2−); (b) solvolysis of ArBr, PhOTf and PhOSO2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document}(CH3)3ŌTf (phenyl ‘betylate triflate’) in super‐acid solvents (FSO3H · SbF5, SbF5, AgSbF6). Analysis of the product mixtures provided no evidence for the intermediacy of phenyl cations as a major pathway in any of the reactions. This result is remarkable, since the ‘betylate’, for example, is a better leaving group by a factor of at least 105than the ‘super’ leaving group triflate in the solvolysis of alkyl sulfonates. These results are a further indication of the extremely low stability of phenyl cations, as well as of the very special properties of the nitrogen leavin

ISSN:0018-019X    

DOI:10.1002/hlca.19830660610

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe evaluation of the dediazoniation kinetics of variousm‐ andp‐substituted benzenediazonium tetrafluoroborates in 1,2‐dichloroethane at 50° in the presence of 18‐crown‐6, 21‐crown‐7 and dicyclohexano‐24‐crown‐8 demonstrates that the rate constant for the dediazoniation within the complex (k2) is smallest, and the equilibrium constant for complex formation(K)is largest for the complexes with 21‐crown‐7(cf. Scheme 1). The logarithms of the equilibrium constants(K)for complex formation with each of the crown ethers studied correlate well withHammett's substituent constants, σ, to give reaction constants ρ = 1.18–1.38.A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (logk2vs.log.k1), found for most substituted diazonium salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p‐Cl,m‐CN),k2was much larger than expected on the basis of the linear logk2vs.logk1relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation.The complexation rate of diazonium salts by crown ethers (kc) is practically diffusion controlled and does not change much with the size of the crown ether. The decomplexation rate (kd), however, is significantly lower for complexes with 21‐crown‐7, than for those with 18‐crown‐6 and dicyclohexano‐24‐crown‐8, and is therefore the reason for the variations in the equilibrium constant(K)and thus for the fact that complexes of arenediazonium salts with 21‐crown‐7 are the most stable.The amounts of the Nα‐Nβrearrangement, as well as those of the exchange of the15N‐labelled diazonio group with external nitrogen during dediazoniation ofp‐toluenediazonium salt were independent of the addition of crown ethers.A dediazoniation mechanism involving a charge transfer, as well as an insertion‐type diazonium ion‐crown ether complex is proposed. In this mechanism, dediazoniation of the insertion complex does no

ISSN:0018-019X    

DOI:10.1002/hlca.19830660611

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY