摘要:

AbstractThe development of a facile, single‐step method for the synthesis of 1,4‐disubstituted piperazine‐2,6‐diones (4) in excellent yields from the corresponding aliphatic, aromatic and heteroaromatic primary amines and iminodiacetic acids (1) is described. A possible mechanism is discussed and the presence of intermediate6ais confirmed by high‐resolution proton NMR spectroscopy. The subsequent two‐step conversion of dione4ainto the deoxygenated 4‐unsubstituted piperazine10in high yield provides an attractive alternative to the currently available (hetero)arylpiperazine synt

ISSN:0165-0513    

DOI:10.1002/recl.19881070402

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe infrared and visible spectrophotometric data of uranyl soaps showed that metaloxygen bonds in uranyl soaps are not purely ionic but are partially covalent in character. The X‐ray diffraction patterns confirmed the double‐layer structure with molecular axes perpendicular to the basal plane. The thermal decomposition of these soaps was found to be kinetically of zero order and the energies of activation were found to lie between 14‐58 k

ISSN:0165-0513    

DOI:10.1002/recl.19881070403

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photochemistry of the series of α‐phenyl β,γ‐enones6–10has been studied under conditions of both direct (λ 300 nm) and triplet‐sensitized irradiation with the aim of determining the reactivity patterns of these “multi”‐chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ‐enones,viz.the 1,3‐acyl shift, affording the corresponding (E)‐ and (Z)‐5‐phenyl‐4‐hexen‐3‐ones, decarbonylation of the radicals formed by α‐cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet‐excited state yielding small amounts of the corresponding acetophenones. The acetophenones are thought to be formed by initial β‐bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6fragment from the 1,4‐ or 1,3‐oxa‐diradical.Upon sensitized irradiation, theo‐methoxy‐ andp‐cyano‐substituted reactants9and10exhibit the di‐π‐methane rearrangement, leading to mixtures of the correspondingcis‐ andtrans‐1‐acetyl‐1‐methyl‐2‐phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively. The formation of the 1,3‐AS and decarbonylation products illustrates the occurrence of α‐cleavage, whereas the acetophenones and di‐π‐methane products are formed via initial aryl‐carbonyl and aryl‐vinyl bridging, respectively.The inability of the other α‐phenyl β,γ‐enones to undergo photocyclopropanation is discussed in terms of excitation‐energy partition. In theo‐methoxy‐ andp‐cyano‐substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ‐enone moiety. Subsequent triplet‐energy dissipation by a free‐rotor mechanism would then account for the stability of these systems. This was observed for (E)‐7 which, upon

ISSN:0165-0513    

DOI:10.1002/recl.19881070404

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe homogeneous sulfonation of 1,2‐dihydroxybenzene (1), its monomethyl (2) and dimethyl ether (3) in concentrated aqueous sulfuric acid at 25°C has been studied and isomer distributions, as well as rate coefficients for the sulfonation of1–3and their monosulfonic acids, have been determined. In 73.5‐87.5% H2SO4,1yields the 3‐ and 4‐sulfonic acids in a ratio of 25:75,2yields the 4‐, 5‐ and 6‐sulfonic acids in a ratio of 46:36:18 in 73.5% H2SO4and 50:39:11 in 87.5% H2SO4, whereas 3 yields only the 4‐sulfonic acid. The remarkable absence of the 3‐sulfonic acid (87.5% H2SO4, the 4‐sulfonic acid of1and the 5‐sulfonic acid of2are present in part in the form of their hydrogen sulfate. In that acid region, the 3‐ and 4‐sulforic acids of1both yield the 3,5‐disulfonic acid, the 4‐ and 6‐sulfonic acids of2both yield the 4,6‐disulfonic acid and the 4‐sulfonic acid of3mainly yields the 4,6

ISSN:0165-0513    

DOI:10.1002/recl.19881070405

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA partial synthesis of the 13‐ethyl‐18‐norsteroid desogestrel is reported. The key step in this synthesis is the intramolecular oxidation of 11β‐hydroxyestr‐5‐ene‐3,17‐dione cyclic bis‐(1,2‐ethanediyl acetal)3with Pb(OAc)4and iodine to 3,3:17,17‐bis[1,2‐ethanediylbis(oxy)]‐11β‐hydroxyestr‐5‐en‐18‐oic acid γ‐lactone2.The 13‐COOH group was then converted into a 13‐ethyl group by a Grignard reaction with methyl‐magnesium bromide followed by Wolff‐Kish

ISSN:0165-0513    

DOI:10.1002/recl.19881070406

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe dimeric products (la‐c) have been prepared by treatment ofN‐oxides derived from some indole alkaloids. Their structures have been elucidated by detailed NMR investigations and the structure of 1c determined by X‐ray analysis. The importance of theE2‐typetrans‐axial elimination of theN‐acyloxy intermediate in the dimer formation has also been established. The iminium salts4a‐band the derived pseudocyanide6have

ISSN:0165-0513    

DOI:10.1002/recl.19881070407

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe preparation and high‐resolution1H NMR conformational analysis of the two novel nucleoside analogues, 1‐(3′‐C‐methyl‐2′‐deoxy‐β‐D‐xylofuranosyl)uracil (compound1) and 9‐(3′‐C‐methyl‐2′‐deoxy‐β‐D‐xylofuranosyl)adenine (compound2), are described. Compounds1and2show a pronounced preference for the north conformation of the sugar ring. The north conformation corresponds with a sterically favoured equatorial location of the methyl group. The C4′ ‐ C5′ conformation in1and2is predominantly γt(transorientation of O5′ and C3′). The configuration at C3′ in1and2was corroborated via a one‐dimensional NOE experiment. The structure of compound1(originally assigned as having the C3′‐methyl group on the β‐fa

ISSN:0165-0513    

DOI:10.1002/recl.19881070408

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe possible effect of hydration of both the enzyme active site and the substrate or product on enzyme complex formation has been evaluated.Replacement of water by organic solvents in the case of highly polar substrates,e.g.carbohydrates, phosphates, sulfates, leads to such an enhancement of enzyme‐substrate and/or enzyme‐product complex stability that there is no measurable conversion. The very low rate of dissociation of the enzyme‐product complex simply prevents these polar‐substrate converting enzymes to be catalytically effective in apolar media. Proper less‐polar substrates, on the other hand, might be more

ISSN:0165-0513    

DOI:10.1002/recl.19881070409

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe jet‐cooled fluorescence properties of two bichromophoric molecules (1and2), differing only in the acceptor chromophore, are compared. The barrier to exciplex formation in1, containing a powerful cyanonaphthalene acceptor chromophore, is much lower than that in2which contains a less powerful naphthalene acceptor chromophore. It is thus proposed that the barrier is not only of a conformational nature, but also related to the energy required for intramolecular charge separation in the Franck‐Condon excited conformation which may then be followed by a fast, electrostatically‐driven conformational c

ISSN:0165-0513    

DOI:10.1002/recl.19881070410

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881070412

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY