摘要:

AbstractThe type of reaction described here, which achieved preparative importance before the turn of the century in the form of the Glaser reaction, has found new applications in recent years: Syntheses of 1,3‐dienes, 2,3,6,7‐tetraaza‐1,3,5,7‐tetraenes, 2,3‐diaza‐1,3‐dienes, hydrazine derivatives, bis(heteroallyl) compounds, hetarenes, polyhetarenes, cyclopolyarenes, protophanes, phanes, and heteraprotophanes. The reaction, which consists in the metalation of the starting substance followed by oxidative coupling of the metal derivative, merits special preparative interest when several successive coupling processes are possible (e. g.polyyne, polyarene, cyclopolyarene, and protophane syntheses). The main factors limiting its applicability are the high thermal stability of some organic copper compounds and the disproportionation of the ligands that frequently occurs as a competing reaction. Selective asymmetric linkages are not generally possible b

ISSN:0570-0833    

DOI:10.1002/anie.197402911

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractDespite sporadic investigations over many years the structures of the pigments responsible for most of the yellow, orange, and brown colors of mammalian hair, and of feathers, have remained unknown. However, recent work has shown that the major reddish‐brown pigments, gallophaeomelanins, are polymers containing benzothiazole and tetrahydroisoquinoline units. The yellow‐orange and violet trichochromes are minor pigments based on a new chromophore, Δ2,2′‐bi(1,4‐benzothiazine). Both groups arisein vivofrom tyrosine and cysteine by a deviation from the biogenetic pathway which normally leads to the formation of eumelanins, the blac

ISSN:0570-0833    

DOI:10.1002/anie.197403051

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe high molecular weight material lignin consists of phenylpropane units linked together by a variety of bond types. During the past eight years, two newly developed degradation procedures have permitted the first direct determinations of the nature of these bonds. The first procedure affords a very mild partial hydrolysis of benzyl ether bonds. Eleven dimeric, trimeric, and tetrameric degradation products were obtained in this way from spruce and beech lignin: they exhibited three different kinds of bonds between the C9structural units, and their structures have all been elucidated. In the second procedure, the most important kind of bond in lignin,i. e.the arylglycerol‐β‐aryl ether bond, can be subjected to directed cleavage under mild conditions after introduction of a suitable neighboring group. On application to beech lignin, 91 % of the material was degraded giving monomeric to tetrameric phenols. Complete structural elucidation of the twenty dimeric phenols isolated and a knowledge of their relative yields and the yields of the other fractions obtained by gel filtration permitted a structural scheme to be set up for beech lignin in which the C9structural units are linked together by no less then ten different kinds of bonds. The structural scheme, which can be readily explained biogenetically, has the same elemental composition as natural beech lignin. Further support for the structural scheme comes from a comparison of the13C‐NMR spectrum of natural beech lignin and a13C‐NMR spectrum calculated for the proposed structure on the basis of about fifty lignin model su

ISSN:0570-0833    

DOI:10.1002/anie.197403131

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe physical properties and the chemical reactivity of the porphyrin macrocycle, whose formation can be rationalized by a simple statistical argument, are related in many respects to those of aromatic hydrocarbons. The reactivity of the porphyrin ligand in its metal complexes varies within wide limits because of the difference in the inductive effects of different central metal ions on the conjugated π‐electron system. One‐electron reactions, phlorin formation by addition of hydrogen or oxygen to the methine bridges, and the formation of π complexes predominate. The biochemical reactivity of the porphyrin ligand largely corresponds to itsin‐vitroch

ISSN:0570-0833    

DOI:10.1002/anie.197403211

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403351

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403361

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403371

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403391

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403401

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197403411

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY