摘要:

AbstractMolecules in which there are neighboring electrophilic and nucleophilic centers are unusually reactive. Oligomerization can be prevented only by bulky groups attached to the main group metal atom that would act as electron pair acceptor, or to the basic non‐metal atom. The basic and the acid centers behave as a single unit in chemical reactions; the system is similar to a “double bond” whose π‐electron density is largely concentrated at one atom. The unsaturated nature of these molecules can be seen in (for example) their addition reactions with hydrogen compounds of non‐metals, or in reactions that are distantly related to cycloadditions at homopolar double bonds. The selection of suitable reaction partners leads to polycyclic, cage‐like molecules containing metal atoms. If these atoms possess lone pairs (as is usual in the lower oxidation states of the third and fourth main groups), these can be utilized to form bonds to further (Lewis acid) metal centers. In some cases large assemblies can be built up from polycyclic systems in this way; a characteristic of these assemblies is a one‐dimensional array of metal atoms. Commonly occurring structural features of the polycyclic species are tetrahedra, trigonal bipyra

ISSN:0570-0833    

DOI:10.1002/anie.198700013

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe evolution of a strategy to synthesize the title compounds is described. Three principal developments allowed realization of this goal: (1) the attainment of high margins of diastereofacial selectivity and regioselectivity in the construction of pyranoid systems via the Lewis acid‐catalyzed cyclocondensation reaction of activated dienes and aldehydes; (2) the exploitation of stereoselective reactions for functionalization of the pyranoid matrix; and (3) the discovery of stereoselective reactions for extending the chiral biases of pyranoid systems to newly emerging stereogenic centers on side chains. The coordination of these components in the synthesis of target systems of high biological interest is describe

ISSN:0570-0833    

DOI:10.1002/anie.198700151

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe aldol reaction is among the most important methods of forming carbon‐carbon bonds. The addition of an enolate to an aldehyde leads to the formation of at least one chiral center. In the case of α‐substituted enolates it has to a large extent been possible to control the product stereochemistry, while the aldol reaction of α‐unsubstituted chiral enolates was for many years a “problem child” for synthetic chemists because of its insufficient stereoselectivity. Progress in this area has only been made in the last few years using either new chiral auxiliaries or alternatives to the ald

ISSN:0570-0833    

DOI:10.1002/anie.198700241

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractIn recent years, various methods have been developed to observe and to influence the course of chemical reactions using laser radiation. By selectively increasing the translational, rotational, and vibrational energies and by controlling the relative orientation of the reaction partners with tunable infrared and UV lasers, direct insight can be gained into the molecular course of the breaking and re‐forming of chemical bonds. Examples for the application of lasers include the synthesis of monomers such as vinyl chloride and polymers such as polyethylene, the synthesis of biologically active substances such as vitamin D3, the separation of isotopes, the removal of impurities, the production of catalysts, glasses, and ceramics, and the deposition and ablation of material on surfaces. Finally, several applications of lasers in medicine are discusse

ISSN:0570-0833    

DOI:10.1002/anie.198700381

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700592

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700611

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700631

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700641

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700651

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198700671

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY