摘要:

AbstractThe crystal structures of four anion cryptates [X−⊂BT‐6H+] formed by the protonated macrobicyclic receptorBT‐6H+with F−, Cl−, Br−and N 3−have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F−‐ion is tetracoordinated, while Cl−and Br−are bound in an octahedron of H‐bonds. The non‐complementarity between these spherical anions and the ellipsoïdal cavity ofBT‐6H+is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N 3−, which is bound by two pyramidal arrays of three H‐bonds, each interacting with a terminal N‐atom of N 3−. The formation constants of the complexes formed byBT‐6H+with a variety of anions (halides, N 3−, NO 3−, carboxylates, SO 42−, HPO 42−, AMP2−, ADP3−, ATP4−, P2O 74−) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F−, Cl−, Br−, and N 3−may be analyzed in terms of the crystal structure data. The cryptandBT‐6H+is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. F

ISSN:0018-019X    

DOI:10.1002/hlca.19840670112

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

Abstractcis‐ andtrans‐(3,6‐D2)‐1,4‐cyclohexadienes1aand1bhave been synthesized fromcis‐3,4‐dichlorocyclobutene (5). Aromatization to benzene with DDQ iscis‐stereospecific with an uncertainty of 5%. This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4‐dihydroaromatics with 2,3‐dichloro‐5,6‐dicya

ISSN:0018-019X    

DOI:10.1002/hlca.19840670113

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

Abstract1‐Arylazonaphthalenes with all the potential cyclopalladation sites (oneperi‐ and threeortho‐positions) substituted by methyl or ethyl groups react with stoicheiometric or catalytic amounts of sodium tetrachloropalladate(II) to the corresponding 2‐arylbenzo[g]indazoles. Possible mechanisms for the catalytic cyclization reaction are p

ISSN:0018-019X    

DOI:10.1002/hlca.19840670114

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

Abstract1n, π*‐Excitation of the γ,δ‐epoxy‐enone (E)‐3leads exclusively to the conformers (Z)‐3A+B. On1π, π*‐excitation of (E)‐3, in addition to (Z)‐3A+B, products6–9arising from a carbene intermediate e are formed. However, products of an isomerizationviaC(γ), O‐bond cleavage of the oxirane were not formed on either mode of excitation. On thermolysis, at 80° the conformer (Z)‐3Ais transformed into (Z)‐3B, which on photolysis returns to (Z)‐3Aand (E)‐3. At 160°, however, (Z)‐

ISSN:0018-019X    

DOI:10.1002/hlca.19840670115

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

AbstractOn triplet excitation (λ>280 nm, acetone), the epoxydiene (E)‐2undergoes (E)/(Z)‐isomerization exclusively, leading to the conformers (Z)‐2Aand (Z)‐2B. On singlet excitation (λ = 254 nm), apart from (Z)‐2A+B, the cyclobutenes3A+Bare formed. However, the epoxydiene (E)‐2does not undergo reactions leading to carbene and C,O‐bond cleavage products, which are normally observed on singlet and triplet excitation, respectively, of the epoxydienes of th

ISSN:0018-019X    

DOI:10.1002/hlca.19840670116

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

AbstractOn1n,π*‐excitation(λ>347 nm), the diastereomeric methanoepoxyenones (E)‐6undergo isomerizationviaC,O‐cleavage of the oxirane leading to diastereomeric photoproducts ((E)‐5→(E/Z)‐13and14; (E)‐6→(E/Z)‐16and17). On1π,π*‐excitation (λ = 254 nm) of either (E)‐5) or (E‐6the photoproducts9, 10and11are formed. By laser flash photolysis (λ = 265 nm) the ylide intermediate3was detected, with a lifetime of 10 μs in MeCN at ambient temperature.Stern‐Volmeranalysis of the ylide quenching by MeOH disclosed that compounds9and10, but not11, ar

ISSN:0018-019X    

DOI:10.1002/hlca.19840670117

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

The Free‐Radical Decomposition ofO,O‐t‐Butyl andO‐Isopropenyl Peroxycarbonate in Solution: the Acetonylation of Esters, Acides and NitrilesThe free‐radical decomposition ofO,O‐t‐butyl andO‐isopropenyl peroxycarbonate in substratres possessing mobile H‐atoms (SH) consists mainly in an induced chain process leading to acetonylated derivatives of the solvent. Fairly good yields are obtained but teh acetonylation of functional substrates often gives mixtures of isomers.In the case of methyl acetate, the acetonylation occurs on the C‐atoms adjacent to the carbonyl (acylox moiety) and to the O‐atom (alkox moiety). However, the relative amounts of the isomeric products depend on the concentration of the peroxycarbonate solutions; at lowest concentration, methyl 4‐oxopentanoate (acyloxy moiety) is obtained selectively. It is assumed that the free radicals issued from the solvent are able to abstract H‐atoms of other molecules of solvent before adding to the double bond of the peroxycarbonate; the more the peroxycarbonate solution is diluted the more the transfers from the C‐atom adjacent to the carbonyl to the radicals adjacent to the O‐atom are favoured. In the case of methyl alkanoates, H‐transfers from the α‐C‐atoms to β‐radicals of teh acyloxy moiety may account for the orientation of the process. Owing to similar H‐transfer processes, the acetonylation of functional esters, of ac

ISSN:0018-019X    

DOI:10.1002/hlca.19840670118

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

AbstractLoganin (1), loganic acid (2), and periclymenoside (3) have been isolated fromLonicera periclymenumL. The structure of the new compound3and the identity of the others have been determined by chemical transformations and interpretation of the spectral data.

ISSN:0018-019X    

DOI:10.1002/hlca.19840670119

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

Formation of Formimidoyl Derivatives from Amines and Benzylisocyanide; A New Possibility of Umpolung for Certain C‐AtomsCu(I)Cl can give a colorless and well‐crystallized complex with 4 molecules of benzylisocyanide. This complex is able to transfer the benzylisocyanide ligands to primary and secondary amines and to formN‐benzylformimidoyl derivatives. Catalyic hydrogenolysis removes the benzyl group, and free formimidoyl compounds are obtained in good yield. The method which succeeds with aliphatic amines, could not be applied to the secondary amino group of tetrahydropte

ISSN:0018-019X    

DOI:10.1002/hlca.19840670120

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY

摘要:

Diastereoisomeric Mutatochromes: Separation, Absolute Configuration, and Spectra and Chromatographic Behaviour(5S, 6R)‐5, 6‐Epoxy‐5, 6‐dihydro‐β, β‐carotent (2), prepared from azafrinal (1) was rearranged in an acid‐catalyzed reaction into the mixture of (5S, 8S)‐ and (5S, 8R)‐5, 8‐epox‐5, 8‐dihydro‐β, β‐carotenes = ‘mutatochrome’. HPLC separation of the individual diastereoisomers led to the pure isomers for the first time. Their structures were assigned by analysis of the characteristic pattern of the signals of HC(7) and HC(8), respectively, in1H‐NMR spectra. Although many reports of the occurrence of ‘mutatochrome’ exist, it is as yet not clear whether optically active or racemic forms predominate in nature. Combination of HPLC separations with UV/VIS and CD spectra should now allow an unambi

ISSN:0018-019X    

DOI:10.1002/hlca.19840670121

出版商:WILEY‐VCH Verlag GmbH    

年代:1984

数据来源: WILEY