摘要:

Conformational Analysis of Free and Complexed Crown Ethers in SolutionThe conformational analysis of the crown ether family by means of n.m.r. spectroscopy is reviewed here. Conclusions about preferred conformations are drawn from dipolar (NOE) and scalar couplings (nJH,H),13C chemical shifts and their temperature dependences as well. Information about the flexibility are available from dynamic n.m.r. spectroscopy and the spin‐lattice relaxation times T1Also conformational variations as result of the complexation of cations or other guest molecules, flexibility variations and the stoichiometry of the complexes obtained can be readily studied by the same n.m.r.‐parameters. Special remarks are referenced to the respective possibilities of CP‐MAS‐13C‐ n.m.r. spectroscopy in the solid state as well as other alternative methods of conformational analysis in solution as are dipole moment measurements and the RAMAN vibrational spectroscopy. The conformational peculiarities of the crown ether family are s

ISSN:0021-8383    

DOI:10.1002/prac.19913330602

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Structure ‐ Chromatographic Retention Relationships of Stereoisomeric Methyl‐substituted IsochromanesRetention times of 13 mono‐, di‐ and trimethylsubstituted isochromanes are determined on both polar (PEG) and nonpolar (OV‐1) stationary phases and KOVATS retention indices (I) are calculated. The significant retention index differences (ΔI) between stereoisomers (up to 30 units) are discussed with respect to the configurational and conformational arrangement of the substituents. Retention indices determined by gas‐solid‐chromatograhpy (GSC) on graphitized thermal carbon black (GTCB) complet

ISSN:0021-8383    

DOI:10.1002/prac.19913330603

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

A New Group of Compounds Derived from Nereistoxin ‐ Synthesis of Bis‐dimethylamino‐tris‐disulfanesThe reaction of organo‐thiosulfates, BUNTE‐salts, with mercaptans is a convenient synthesis of disulfanes. Similarly bis‐BUNTE‐salt7and tert. butyl mercaptan give bis‐disulfane5c[9]. By treating7with several aliphatic mercaptans we found the formation of the tris‐disulfanes8a–din preparative amounts in addition to the bis‐disulfanes5a–dexpected. This reaction was investigated. The preparation of the compounds8is described and a proposal is given for a mechanism of the formation of8as a th

ISSN:0021-8383    

DOI:10.1002/prac.19913330604

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

ISSN:0021-8383    

DOI:10.1002/prac.19913330605

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Synthesis and Structure of Imino‐bis[1]benzothiopyrano[4,3‐b:4,3‐f][1,5]dithiocinesSeveral substituted 3‐Alkyl‐ respectively 3‐Aryl‐aminomethylene‐2H‐[1]benzothiopyran‐4‐thiones undergo a thermal reaction yielding the light yellow title compounds2. For the mechanism of this reaction we propose a condensation reaction of the starting compounds1loosing one molecule of amine in the first step followed by electrocyclisation reactions of the intermediates to products2. The structure of compounds2is elucidated by1H nmr spectroscopy and also x‐ray analysi

ISSN:0021-8383    

DOI:10.1002/prac.19913330606

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Novel Steroidal Orthoesters by Intramolecular Cyclisation of Ethynylcarbinol Derivatives with Organic HypoioditesThe iodination of the 17β‐acetoxy‐17‐ethynylsteroid2using iodine/copper(II)‐acetate in combination with the nucleophiles acetic acid, water and methanol is reported. Examples for chemical modification of the products are described. A cyclisation occurs in the case of iodomethoxylation as a formal through‐space 1.4‐addition of the reagent forming a mixture of 4 isomer iodomethylen‐1,3‐dioxolanes. The configuration and ratio of the isomers as well as analytical data of this hitherto unknown dioxolane

ISSN:0021-8383    

DOI:10.1002/prac.19913330607

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Synthesis and Properties of Methyl‐2‐methoxycarbonylmethylene‐ and ‐2‐(formyl‐ methoxycarbonylmethylene)‐2H‐thiopyran‐3‐carboxylatesDimethyl‐2‐chloro‐propene‐l,3‐dicarboxylate is a easily available reactive C2‐building block for the synthesis of 2H‐thiopyran derivativesla—nin good yields via [C3S + C2]‐cyclisation reactions using β‐thioxoaldehydes and their derivatives as C3S‐synthons. The structure of the stable red products with Z‐configuration (side chain in position 2 of the ring) is elucidated by means of several analytical and spectroscopic methods including X‐ray analysis of compounds1handlk.Treating of1with Vilsmeier reagent yields title compounds2with a remarkable less reactive formyl group at the exo‐methylene group. There is obviou

ISSN:0021-8383    

DOI:10.1002/prac.19913330608

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

ISSN:0021-8383    

DOI:10.1002/prac.19913330609

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractHomochiral 3‐alkylated (2R,3R)‐ and (2R,3S)‐2,3‐dihydroxyalkyl p‐toluenesulfonates (9and10) are essential building blocks for vitamin D3metabolites with a modified side chain. Nine of these compounds have been prepared starting from (R)‐2,3‐O‐cyclohexylideneglyceraldehyde (1) by addition of alkylmagnesium halides, Jones oxidation of the obtained diastereomeric alcohols2and3to the corresponding ketones4, and a second addition of alkylmagnesium halides, followed by hydrolytic removal of the cyclohexylidene group and selective tosylation. The opposite diastereoselectivity of the two Grignard reactio

ISSN:0021-8383    

DOI:10.1002/prac.19913330610

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Preparation of Benzo[c]thiophenes Using a Modified Hinsberg‐ReactionWhereas the tetrahydrobenzo[c]thiophenes3and6are easily obtained from1and2or4their dehydrogenation (i. e. aromatization) is difficult and the yields are low. However, the method allows to prepare hitherto unknown benzo[c]thiophenes with special substituents in the 1,3‐positi

ISSN:0021-8383    

DOI:10.1002/prac.19913330611

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY