摘要:

AbstractNucleophilic ring‐opening reactions of 3‐alkylaziridine‐2‐carboxylic esters are described. Without ring activation at nitrogen, ring opening could only be accomplished with ethereal hydrogen chloride. Introduction of electron‐withdrawing activating groups at the nitrogen atom was necessary. Three types of activating groups were used,viz. acyl, alkoxycarbonyl and sulfonyl groups. In the presence of a Lewis‐acid catalyst, ring opening with two nucleophiles, namely indole and benzenethiol, could be accomplished.SN2‐type attack at C3 was observed exclusively. With Brönsted acids (hydrogen chloride, formic acid, acetic acid), ring opening could also be effected. 3‐Formyloxy derivatives could also be prepared by reaction of the activated aziridines withN,N‐dimethyl‐formamide in the presence of boron trifluoride etherate. Reaction with sodium azide caused some difficulties; complex product mixtures were usually obtained.N‐Sulfonylaziridine‐2‐carboxylic esters gave a mixture of the two possible regioisomers, resulting from attack at C2 and C3. Treatment ofN‐sulfonylaziridine‐2‐carboxylic esters with trimethylsilyl azide, however, gave products exclusively ring‐opened at C2. On reaction of the activated aziridines with acetonitrile in the presence of boron trifluoride etherate, a ring‐expansion reaction was observed, leading to imidazolines. On standing, these heterocyclic compounds slowly hydrolyzed to α,

ISSN:0165-0513    

DOI:10.1002/recl.19921110201

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

Abstract3‐Aryl‐3‐azido‐2‐hydroxypropanoic esters, prepared from the corresponding 3‐aryl‐oxirane‐2‐carboxylic esters by ring opening with sodium azide, were reduced with tin(II) chloride dihydrate in methanol to give 3‐amino‐3‐aryl‐2‐hydroxypropanoic esters in good yields. Under these conditions, halogen substituents in the aromatic rings were not affected. The nitro group, however, was partially reduced to the amino group. Treatment of aliphatic oxirane‐2‐carboxylic esters with acetonitrile in the presence of boron trifluoride etherate led to regiospecific formation of 2,4‐dialkyl‐2‐oxazoline‐5‐carboxylic esters, resulting from reaction of the nitrile at C3. Acidic hydrolysis of these oxazoline‐5‐carboxylic esters gave the corresponding 3‐(acylamino)‐2‐hydroxy carboxylic esters. With these two complementary methods, both aryl‐ and alkyl‐substi

ISSN:0165-0513    

DOI:10.1002/recl.19921110202

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAziridine‐2‐carboxylic esters1were converted into 2H‐azirine‐2‐carboxylic esters4in two steps. Treatment of1withtert‐butyl hypochlorite in ether gave smoothN‐chlorination. Reaction ofN‐chloroaziridines2with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) or 1,4‐diazabicyclo[2.2.2]‐octane (DABCO) gave2H‐azirine‐2‐carboxylic esters4in moderate yields, with concomitant formation of aziridines1. Aziridines1could readily beN‐brominated withN‐bromosuccinimide. Treatment ofN‐bromoaziridines3with base, however, did not lead to azirine formation.N‐Halogenated aziridines2and3exist as mixtures of invertomers

ISSN:0165-0513    

DOI:10.1002/recl.19921110203

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe photochemistry of the α‐bis(methoxyimino)alkanes1–5and the, structurally related, conjugated dihydro(methoxyimino)isoxazoles6and7was studied. Triplet‐photosensitized irradiation of1–7leads only to stepwiseE‐Zisomerization. Photostationary‐state (pss) ratios for1,6and7are reported for the various applied triplet sensitizers. Direct irradiation with 254 nm leads to bothE‐Zisomerization (which is the dominant reaction) and formation of products resulting from initial N‐O homolysis of the excited singlet ππ* state. Mechanisms for the formation of the various products are proposed and the relative importance of the various steps is indicated and discussed. For the α‐bis(methoxyimino)alkanes1and3, only the (E,Z)‐isomer undergoes N‐O homolysis. With the (methoxyimino)isoxazolines6and7, only the exocyclic NO bond exhibits homolysis and not t

ISSN:0165-0513    

DOI:10.1002/recl.19921110204

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction between isocyanates and carboxylic acids is known to lead to amides. We have studied the mechanism of catalysis of this reaction by phospholene oxides.The reaction between phenyl isocyanates and benzoic acid was monitored under various conditions using High‐Pressure Liquid Chromatography. It was found that the catalyst reacts with the iso‐cyanate under formation of a carbodiimide. The carbodiimide reacts with the carboxylic acid to form amide and isocyanate via anN‐acylurea as intermediate. The catalyst is partly deactivated by the acid. The phospholene catalyst was only found effective in reactions with aromatic isocya

ISSN:0165-0513    

DOI:10.1002/recl.19921110205

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

Abstract7E,13E‐11,19‐10,20‐dimethanoretinal (1) and its 13Zisomer2were prepared from β‐ionone, using the novel synthon 2‐(diethoxyphosphinyl)‐5,5‐dimethoxyhexanenitrile. This synthon was also used to prepare7E,9E,13E‐10,20‐methanoretinal (3) and its 13Zisomer4in high yield, starting from β‐ionone. Spectroscopic analysis (mass,1H and13C NMR and UV/Vis) of these compounds is discussed. The introduction of the methano bridges leads to minimal steric and electronic changes. The photostationary state reached from1and2has the 13Zform2as the main constituent. This is one of the very few with aZform as the main constituent of the photostationary state.1and2are very sensitive to acid‐catalyzed isomerization of the 13‐C14‐C double bond. The presence of the 11,19‐methano bridge is responsible for

ISSN:0165-0513    

DOI:10.1002/recl.19921110206

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractImmobilized and fully protected oligodeoxynucleotides containing a 4‐(1,2,4‐triazolyl)‐thymidine residue at a predetermined position were prepared according to a well‐established phosphite triester methodology using 2‐cyanoethyl phosphoramidites of a 4‐(1,2,4‐triazolyl)‐substituted thymidine and standard protected nucleosides. Treatment of the immobilized oligomer with methanol, ethanol orn‐propanol in the presence of DBU at 50°C gave the corresponding oligonucleotides containing 4‐methoxy, 4‐ethoxy‐ or 4‐

ISSN:0165-0513    

DOI:10.1002/recl.19921110207

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractSome new low‐valent, cationic complexes of technetium‐99 have been prepared. Oxidation of Tc2(CO)10(1) with NOPF6in acetonitrile gave [Tc(CH3CN)(CO)5]PF6(2) quantitatively. This complex constitutes a useful precursor for cationic carbonyl complexes, as exemplified by a variety of reactions with bi‐ and tridentate ligands from which air‐stable, water‐soluble complexes of type [LTc(CO)3]+(L = 1,4,7‐triazacyclononane, 1,4,7‐trimethyl‐1,4,7‐triazacyclononane and 1,4,7‐trithiacyclononane) have been isolated and characterized. A series of mixed complexes of technetium(I) of general formula {Tc(N,N)[P(OR)3]2(CO)2}PF6(N,N = 2,2′‐bipyridine, 4,4′‐dimethyl‐2,2′‐bipyridine and R = methyl,

ISSN:0165-0513    

DOI:10.1002/recl.19921110208

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110210

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19921110212

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY