ISSN:0165-0513    

DOI:10.1002/recl.19941130702

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe usefulness of molecular‐mechanics calculations in the study of the conformational properties of several tetraarylporphyrins and diarylporphyrins is demonstrated. Energy‐minimized conformations and rotational barriers of several substituted and unsubstituted arylporphyrins correspond very well with experimental resu

ISSN:0165-0513    

DOI:10.1002/recl.19941130703

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractInversion of configuration at the benzylic hydroxyl group of (1S,2S)‐pseudoephedrine (2) to afford (1R,2S)‐ephedrine is known to be a difficult process. The Mitsunobu reactions of1and2might offer a route to achieve such inversions. In fact Mitsunobu reactions on1and2are known to proceed via aziridines formed on intramolecularSN2 substitution by the amine functionality. The Mitsunobu reactions of N‐methylated and N‐benzylated ephedrines have been found to proceed via the corresponding aziridinium ions. These aziridinium ions can be opened (SN2 substitution) by nucleophiles like phthalimide and thiols. Intramolecular participation in2can be avoided by use of thetert‐butyloxycarbonyl‐ (BOC) or benzyloxycarbonyl‐ (CBZ) protected derivatives. Mitsunobu reactions on these derivatives lead to inversion of configuration at the benzylic hydroxyl center. In contrast the BOC and CBZ derivatives of1are deprotected under Mitsunobu conditions. The Mitsunobu reactions ofthreo(1S,2,S)‐2‐amino‐1,3‐propanediol have also been examined. An attempt to achieve protection by reaction with dimethylformamide dimethyl acetal led to the more substituted 2‐oxazoline as established by X‐ray crystallography. The desired inversion of configuration of the benzylic hydroxylic group was eventually achieved by protection of the amino substituent as the phthalimide and protection of the primary hydro

ISSN:0165-0513    

DOI:10.1002/recl.19941130704

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractDialkylcarbodiimides in the presence of a Cu1catalyst react cleanly with the hydroxyl group of N‐methylated (1R,2S)‐ephedrine and (1S,2S)‐pseudoephedrine. These adducts react with nucleophiles like alkyl and aryl thiols as well as thioic acids and phthalimide to form the substitution products with overall retention of configuration. It is postulated that intramolecular participation of the amino group via anSN2 reaction leads to aziridium salts, which are subsequently opened by the nucleophiles via a secondSN2 reaction. This synthetic approach is also useful for the inversion of simple secondary alcohols; on treatment with dicyclohexylcarbodiimide followed by benzothioic acid and treatment with LiAlH4, menthol was converted in good yield to neomenthane

ISSN:0165-0513    

DOI:10.1002/recl.19941130705

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper we report the preparation of specifically2H‐labelled L‐glutamic acids and2H‐,15N‐,13C‐labelled L‐glutamines on the gram scale. The products obtained have high isotope enrichment (>98%) and high optical purity. The synthetic schemes allow the specific isotope enrichment of every H, C, and N position or any combination of positions. (2‐2H)‐L‐Glutamic acid was synthesized by enantioselective enzymatic conversion of 2‐oxoglutaric acid using glutamate dehydrogenase (GDH, E.C. 1.4.1.3.), alcohol dehydrogenase (ADH, E.C. 1.1.1.1.) and (2H6)ethanol. (3,3‐2H2)‐L‐Glutamic acid was prepared by enzymatic conversion of 2‐oxo‐3,3‐di‐deuteroglutaric acid which was easily obtained from 2‐oxoglutaric acid by an isotope exchange reaction in2H2O at pH 13.0. (4,4‐2H2)‐L‐Glutamic acid was obtained by chemical exchange in 20%2HCl. Four different isotopomers of L‐glutamine [(2‐2H)‐, (3,3‐2H2)‐, (4,4‐2H2)‐, and (5‐13C)‐L‐Gln] were synthesized by the enantioselective conversion of isotopically labelled L‐glutamic acids using glutamine synthetase (GS, E.C. 6.3.1.2.). The amide group of glutamine was labelled with15N using15NH4Cl in the enzymatic reaction. The labelled L‐glutamic acids and L‐g

ISSN:0165-0513    

DOI:10.1002/recl.19941130706

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe regioselective synthesis of dimethyl 1,3,5‐cyloheptatriene‐1,2‐dicarboxylate (4) was achieved by a ring expansion method, starting from dimethyl 1,3‐cyclohexadiene‐2,3‐dicarboxylate (5). The title compound3was obtained as an air‐sensitive oil by zinc‐copper reduction of 1,2‐bis(bromomethyl)cyclohepta‐1,3,5‐triene (10) to which the di

ISSN:0165-0513    

DOI:10.1002/recl.19941130707

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19941130708

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19941130710

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19941130712

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19941130714

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY