摘要:

AbstractThe phosphites of methyl α‐D‐ and methyl β‐D‐ribopyranoside were prepared from the corresponding methylglycosides according to the method ofStetterandSteinacker1. The mass spectra of the isomeric phosphites, which are markedly different, and the NMR spectral data are in agreement with the proposed s

ISSN:0165-0513    

DOI:10.1002/recl.19770961202

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

Abstract13C‐NMR chemical shifts of substituted squalenes and model compounds with a heteroatom in δ‐position to a double bond show that a steric interaction exists between the hetero‐atom and the double bond. This points to the presence of “precoiled” conformations in the hetero‐substituted squalenes and also in squalene itself. The nature of the interaction remains veiled, but it appears to be a general feature as is shown in a series of 2‐ and 3‐substituted thiophenes with a double bond i

ISSN:0165-0513    

DOI:10.1002/recl.19770961203

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractThe synthesis of the gastrointestinal hormone secretin, a heptacosapeptide, and analogues by the Repetitive Excess Mixed Anhydride (REMA) method was monitored by reverse‐phase high‐performance liquid chromatography (HPLC). All intermediate protected peptides were thus purified on a micro‐preparative scale (100‐200 μg, ≥ 20 nmole).The method allowed the separation of the protected diastereoisomeric [L‐Ala4]‐ and [D‐Ala4]‐des‐His1‐secretin.An aspartyl‐glycyl rearrangement could be detected in the protected pentacosa‐, hexacosa‐, and

ISSN:0165-0513    

DOI:10.1002/recl.19770961204

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractBF2complexes of alkylated pyrromethenes were prepared by reacting the corresponding pyrromethenes with BF3·OEt2under basic conditions. A striking aspect of these complexes is a pronounced fluorescence in organic solvents, even at room temperature, with fluorescence quantum yields between 0.3‐0.8. The efficiency and wavelength maximum of the fluorescence seems to be correlated with the substitution pattern at the 2 and 6 position. In none of these systems could phosphorescence be detect

ISSN:0165-0513    

DOI:10.1002/recl.19770961205

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractA cyclopropyl cation, stabilized by ap‐anisyl groupAnisyl = methoxyphenyl., turns out to be an intermediate in the alcoholysis of 1‐(p‐anisyl)cyclopropyl halides. In other reactions with nucleophiles substitution products are also formed predominantly without ring rupture.The influence of the solvent, nature of nucleophiles and added salts on reaction rates and product distributions support an SN1 type mech

ISSN:0165-0513    

DOI:10.1002/recl.19770961206

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

摘要:

AbstractCyclopropyl chlorides with a methoxy‐ or ap‐tolyl group linked to the same carbon atom as halogen undergo substitutions in polar solvents with relatively little ring rupture, when the nucleophile is sufficiently reactive (e.g.methanol, N−3, Br−) to trap the intermediate α‐substituted cyclopropyl cations.Such substitution reactions are of the SN1 type and do not proceedviacyclopropene intermediates. With poor nucleophiles such as NO−3in aqueous acetone, only polymeric ring‐opened produ

ISSN:0165-0513    

DOI:10.1002/recl.19770961207

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19770961208

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19770961201

出版商:WILEY‐VCH Verlag    

年代:1977

数据来源: WILEY