ISSN:0165-0513    

DOI:10.1002/recl.19800990102

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractEffects of substituents in diene and dienophile on the regio‐ and stereo‐selectivity of Diels‐Alder reactions have been studied on cycloadditions of alkoxy‐substituted 1,3‐butadienes (1) and 2‐substituted cyanoethenes (2). The regioselectivity is always very high, and is determined by the magnitude of the orbital coefficients of the interacting carbon atoms according to the frontier orbital theory. The stereoselectivity is more determined by steric factors than by secondary orbital overlap. The results point to a transition state, in which the planes of diene and dienophile, are non‐parall

ISSN:0165-0513    

DOI:10.1002/recl.19800990103

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractSulfur dichloride adds to vinylic ethers to give 2,6‐dichloro‐1,4‐oxathianes. Dehydro‐halogenation of these products leads to the hitherto unknown heterocyclic compounds 1,4‐oxathiin6and 3,5‐dimethyl‐1,4‐oxathiin 7 in good

ISSN:0165-0513    

DOI:10.1002/recl.19800990104

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

Abstract13C FT single resonance spectra are obtained for two isomers of 2,6‐dichloro‐1,4‐oxathiane; one of the isomers is a racemic mixture. From a combined study of the various long‐range carbon‐proton coupling constants the conformations of both isomers could be determined. Each isomer exists in two conformers which are in a rapid interconversion equilibrium. Contrary to predictions based on the “anomeric‐effect”,cis‐2,6‐dichloro‐1,4‐oxathiane in the liquid phase is predominantly in thecis

ISSN:0165-0513    

DOI:10.1002/recl.19800990105

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

Abstractβ,β‐Dimethylaspartic acid was obtained by the aluminium‐amalgam reduction of theO‐methyloxime of diethyl 2‐oxo‐3,3‐dimethyl‐1,4‐butanedioate and subsequent hydrolysis. The (latter) diester was conveniently prepared by the condensation of ethyl 2‐bromo‐2‐methylpropionate with diethyl oxalate, under the influence of magnesium. β,β‐Difluoroaspartic acid,threoβ‐methylaspartic acid and β,β‐dimethylaspartic acid (as racemates) were coupled with 6‐chloropurin‐9‐yl riboside to yield the corresponding nucleosides. The bases methyl 7‐oxo‐7H‐pyrido[2.1‐i]purine‐9‐carboxylate and 6‐[2,3‐bis(methoxycarbonyl)propyl]purine were converted into the corresponding nucleosides by coupling with O2,O3,O5‐tribenzoylribofuranosyl chloride and removal of the protecting groups. T

ISSN:0165-0513    

DOI:10.1002/recl.19800990106

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractMetallation of 2H‐thieno[2,3‐b]thiopyran1by strong bases under relatively apolar conditions proceeds exclusively in the 2‐position of the thiophene ring. In polar media a 2‐proton of the thiopyran ring is removed to give the anion1b. By addition of hexamethylphosphoric triamide (HMPT) to the lithiated compound1aconversion into1btakes place. The anions1aand1breact with methyl iodide to give the compounds2and3, respectively. Compound2can be further methylated by reaction with BuLi in tetrahydrofuran (THF)/HMPT mixtures or sodamide in liquid NH3, followed by addition of methyl iodide. The resulting compound4can be converted into the compounds5,6or7, depending on the base‐solvent system: Compound5is produced by interaction between4and KNH2in liquid NH3at − 33°, followed by methylation at − 60°. If the reaction with KNH2is carried out at − 60°, however, methylation gives6, this result is also obtained from4, BuLi in THF/HMPT and CH3I. Omission of HMPT during the metallation gives rise to vinylic proton abstraction, and subsequent addition

ISSN:0165-0513    

DOI:10.1002/recl.19800990107

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractDie Bildungsreaktion der Millonschen Base wird infrarotspektroskopisch untersucht. Es gelingt, die Reaktion auf der Stufe des Imin‐Monohydrates abzufangen. Durch Trocknung desselben ist es möglich, zum Amin zu gelangen. Das Amin‐Spektrum wird mitgeteilt. Auch das Diammin konnte hergestellt und dessen Spektrum aufgenommen we

ISSN:0165-0513    

DOI:10.1002/recl.19800990108

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractAddition of 9,10‐phenanthrenequinone or 3,5‐di‐tert‐butyl‐o‐benzoquinone toN,N‐dialkyl‐3‐alken‐1‐ynyl‐1‐amines R2‐CHCH‐C≡C‐NR12(4) gives quinoid α‐alkenyl‐γ‐oxo‐α,β‐unsaturated carboxamides6or8, respectively; these undergo a spontaneous ring‐closure, or can be cyclised photochemically into 2H‐phenanthro[9,10‐b]py

ISSN:0165-0513    

DOI:10.1002/recl.19800990109

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19800990101

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY