摘要:

AbstractThe development and the application of enzyme‐catalyzed transformations for the introduction and/or removal of protecting groups for hydroxyl‐, amino‐, mercapto‐ and carboxy functions is discussed. The various examples highlight the advantageous application of enzymes in comparison to classical chemical techniques in the chemistry of peptides, carbohydrates, alkaloids and steroids. Thus, the biocatalysts not only complement the arsenal of classical chemical methods, but offer viable and interesting alternatives

ISSN:0941-1216    

DOI:10.1002/prac.19933350202

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractChlorination of 1‐substituted 3‐formyl‐4‐hydroxy‐2‐quinolones (1a,b) with phosphorylchloride leads to 4‐chloro‐3‐dichloromethylquinolones (2), which can be hydrolyzed to 4‐chloro‐3‐formyl‐quinolones (4). From the anilinomethylene quinolinediones (3), at low temperatures the formylquinolones4can be obtained directly, whereas at high temperatures cleavage of the tautomeric azomethine moiety followed by subsequent ring closure to the naphthyridines (7) takes place. With 1‐unsubstituted 3‐formyl‐4‐hydroxy‐2‐quinolones (1d) either the 3‐dichloromethylquinolone (2d) or the 2,4‐dichloro‐3‐dichloro‐methylquinoline (10) is obtained depending on the reaction conditions. Similar results are obtained with the 1‐unsubstituted anilinomethylene compounds (3). Attempts to obtain the 3‐formyl‐2,4‐dichloroquinoline (11) were unsuccessful because in all experiments

ISSN:0941-1216    

DOI:10.1002/prac.19933350203

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThirteen Schiff base salts in the class of compounds represented by retinal pyrrolidinium perchlorate were prepared (most of them for the first time), fully characterized analytically and spectroscopically, and examined in the 30–100 GHzrange with respect to their putative ability to absorb radar signals. While some signal loss was noted with salts having I3−counterions, the compounds of this class show negligible potential as components of radar‐absorbing coating sy

ISSN:0941-1216    

DOI:10.1002/prac.19933350204

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractAcceptor substituted vinylic t‐butyl sulfoxides behave in acidic medium as formal vinylthiyl cations. These electrophilic species add to olefins, hexyne and allene to form β‐trifluoroacetoxy‐sulfenylation pro

ISSN:0941-1216    

DOI:10.1002/prac.19933350205

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Crystal Inclusion of Oligocyclic Anhydrides Containing 9,10‐Dihydro‐9,10‐ethanoanthracene Constructional Units – Crystal Structure of a Benzene ClathrateA series of rigid oligocyclic anhydrides comprising a characteristic 9,10‐dihydro‐9,10‐ethanoanthracene framework have been shown to form crystalline inclusion compounds (clathrates) with small organic molecules, in particular of five‐ and six‐membered ring types. Inclusion formation depends on the number of substituents (bromine atoms). The X‐ray crystal structure of the clathrate4· benzene (2:1) is reported: monoclinic (P21/c),a= 8.599(4),b= 9.732(5),c= 21.023(10) Å, β = 92.03(4)°,Z= 4. The benzene guest molecules are located in lattice cavities between the bulky host molecules around the crystallographic symmetry centres, and are somewhat disordered. The cocrystal is held together by weak van der Waals forces. The structural model refined toR= 0.046 for 1903

ISSN:0941-1216    

DOI:10.1002/prac.19933350206

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

2‐Substituted 1,6‐Methano[10]annulenes as Dienophiles in the [4 + 2]Cycloaddition with Inverse Electron DemandThe LUMO‐diene‐controlled [4 + 2] cyclo‐additions of various at C‐2 substituted 1,6‐methano [10]annulenes6,10and13with the electron‐deficient s‐cis‐fixed diazadiene system of 3,6‐bis(trifluoromethyl)‐1,2,4,5‐tetrazine(3)are described. With the donor substituted6(or its valence tautomer7)3reacts under unusually mild conditions to give the 7,12‐methanocyclodeca[d]pyridazine9with high site selectivity. The Diels‐Alder reaction of3with the 2‐bromo‐1,6‐methano[10]annulene (10⇌11) leads to the 6‐ and 8‐bromo‐7,12‐methanocyclodeca[d]pyridazines12aand12b, whereas with the various acceptor substituted species13⇌14the 8‐substituted 7,12‐methanocyclodeca[d]pyridazines15a–care formed exclusively. Spectroscopic data show, that for all the novel methanocyclodeca[d]pyridazines9,12and15the annulenic structure is dominating, but a remarkable reduction of the ring current and a distinct bond alternation is obs

ISSN:0941-1216    

DOI:10.1002/prac.19933350207

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

New Pyoverdin Siderophores fromPseudomonas putida CFour new pyoverdins (C 2A, C 2B, C 3A, C 3B) were isolated from cultures ofPseudomonas putida C. Their structures were elucidated by chemical and spectroscopic methods. The compounds consist of a chromophore – (1S)‐5‐amino‐2,3‐dihydro‐8,9‐dihydroxy‐1H‐pyrimido [1,2‐a]quinoline‐1‐carboxylic acid – substituted at the amino group with a dicarboxylic acid or its amide. The carboxyl group of the chromophore is amidically bound to the N‐terminus of L‐Asp‐D‐[N5‐hydroxy‐N5‐(D‐β‐hydroxybutyryl)] Orn‐D‐Dab‐L‐Thr‐Gly‐D‐Ser‐L‐Ser‐L‐threo‐β‐hydroxy‐Asp‐L‐Thr. The four pyoverdins differ only in the nature of the dicarboxylic acid (amide),viz.L‐malamoyl‐ (C 2A), succinamoyl‐ (C 2B), L‐3‐carboxy‐2‐hydroxypropanoyl‐ (C 3A) or 3‐carboxypropanoyl (C 3B) residue. The hydroxamate function consists of N5‐hydroxy‐Orn and β

ISSN:0941-1216    

DOI:10.1002/prac.19933350208

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Ring Transformations of Pyrazolinones via Azoolefins – a New Way to the 1,2,3‐Thiadiazol‐SystemElektrophilic attack of thiocyanate/bromine to azoenamine (2a) yields thiocyanato compound3awhich cyclizes into 1,2,3‐thiadiazolium‐salt (5a) on treatment with perchloric acid. 2‐Halo‐3‐arylazo‐propenamides (8) form directly thiadiazolium‐salts (11) with KSCN/HOAc. The addition of N‐ or O‐nucleophiles to11occurs in the 5‐position to form

ISSN:0941-1216    

DOI:10.1002/prac.19933350209

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Organic Syntheses Based on 2‐Oxoglutaric Acid. II. On the Synthesis of Heterocycles by Reactions of Dimethyl 3‐bromo‐2‐oxoglutarate with BinucleophilesReactions of dimethyl 3‐bromo‐2‐oxoglutarate2with binucleophiles to form heterocycles proceed on two different pathways depending on the type of reactant. Thus, strong S‐nucleophiles like thioureas and thiocarbohydrazide substitute initially the bromine atom and form 2‐aminothiazoles3–7and the 1,3,4‐thiadiazine8. However, o‐phenylendiamines reacted to form the brominated quinoxaline‐2(1H)‐

ISSN:0941-1216    

DOI:10.1002/prac.19933350210

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractWater soluble palladium(II) complexes of the type PdCl2(phosphine)2with sulfonated phosphines as ligands catalyse the reductive dehalogenation of allyl or benzyl halogenides by means of formates in a biphasic water/heptane system. This reaction can be promoted by addition of polyethers of different types as phase transfer catalysts. Enhancement of reaction rate and control of selectivity are investigated in the reductive conversion of (E)‐Ph‐CH  CHCH2Cl leading to (E)‐Ph‐CH  CH‐CH3and Ph

ISSN:0941-1216    

DOI:10.1002/prac.19933350211

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY