摘要:

AbstractXanthenyl and thioxanthenyl halides added readily to asymmetric diarylethylenes and their 2‐halogeno‐derivatives to give after dehydrohalogenation 1,1‐diaryl‐2‐[xanthen(orthioxanthen)‐9‐yl]‐ethylenes and 1,1‐diaryl‐2‐halogeno‐2‐[xanthen(or thioxanthen)‐9‐yl]‐ethylenes. The thioxanthenylethylenes were also obtained by another way.Reactions of these ethylenes with bromine, chlorine or sulfuryl chloride were influenced by the halogen and the nature of thep‐substituent.Dehydrohalogenation of the 2‐halogenoxanthenyl(or thioxanthenyl) ethylenes gave the corresponding 1,1‐diaryl‐2‐[xan

ISSN:0018-019X    

DOI:10.1002/hlca.19730560602

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractDiethyl or dimethyl benzyloxycarbonylaminomalonate was reacted with ring substituted benzyl halides and the resulting arylalkyl derivatives (3to6) half‐saponified to theDL‐monoacid‐monoesters (7to10). Decarboxylation by refluxing in dioxane afforded the N‐benzyl oxycarbonyl‐DL‐amino acid esters (11to14), which were resolved into their optical antipodes by enzymic hydrolysis of the ester group with Subtilisin, typeCarlsberg. Enzymic hydrolysis led to the N‐benzyloxycarbonyl‐L‐amino acids (15to18) and to the correspondingD‐amino acid esters. The latter were converted to the N‐benzyloxycarbonyl‐D‐amino acids (19and20) by alkaline hydrolysis of the ester groups. These derivatives could be used directly for further peptide synthesis. The following compounds were prepared: N‐benzyloxycarbonyl derivatives ofp‐methyl‐L‐phenylalanine (15),p‐methyl‐D‐phenylalanine (19),p‐fluoro‐L‐phenylalanine (16),m‐fluoro‐L‐phenylalanine (17),m‐fluoro‐D‐phenylalanine (20) and penta‐fluoro‐L‐phenylalanine (18). The free amino acids were obtained by

ISSN:0018-019X    

DOI:10.1002/hlca.19730560603

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractESR. data are reported for the radical anions (II⊖to VI⊖) of five alkyl substituted6a‐thiathiophthenes. Rates and activation parameters for the inversion of the 3,4‐trimethylene chain in IV⊖, V⊖and VI⊖have been obtained by means of an iterative least squares computer program ESRCEX. Preferential conformations of the alkyl substituents are discussed in terms of the 〈cos2θ〉 dependence of the β‐proton coupling constants and with the aid of molecular models. Experimental evidence strongly suggests that the partial rotation of the ethyl and isopropyl groups in V⊖and VI⊖is correlated with the inversion of t

ISSN:0018-019X    

DOI:10.1002/hlca.19730560604

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractN(2)‐alkylated indazoles are known to undergo two different photoreactions, namely (i) rearrangement into benzimidazoles in organic solvents and neutral aqueous solution, and (ii) solvolysis yieldingo‐amino‐benzaldehydes or acetophenones, in strongly acidic solution.In diluted acidic solution (pH 3–4) both of these reactions are suppressed and a new photoreaction takes place, leading to two isomeric dihydroazepinones.Irradiation of 2,3‐dimethyl‐indazole in diluted sulfuric acid (pH = 3.8) yields 7‐acetyl‐1,3 dihydro‐2H‐azepin‐2‐one and 3‐acetyl‐

ISSN:0018-019X    

DOI:10.1002/hlca.19730560605

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe cleavage of a single SO2O bond occurs during the polarographic reduction of a tosyloxy group (pCH3C6H4SO2O = TsO) in aprotic medium and intramolecular cyclisation may ensue when a second TsO group is present on the same molecule. The polarographic behaviour of aliphatic ditosyloxy derivatives is discussed on the assumption thatoriented vicinal derivativesat the interface assume a conformation which resembles the geometry of the transition state for an intramolecular elimination with anchimeric assistance of one of the tosyloxy groups. This situation favours the electron transfer, whereas the same geometric requirements hinder the intramolecular interaction of the TsO groups of theorientednon‐vicinal derivatives. This interpretation agrees well with the fact that the large scale electrolysis of vicinal ditosyloxy derivatives give much higher yield of cyclic ethers than the higher homologues. It is also shown that intramolecular interaction between TsO groups can occur through an intervening double bond in a non‐vicinal der

ISSN:0018-019X    

DOI:10.1002/hlca.19730560606

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe activation parameters of the thermal rearrangements of thetrans‐divinylcyclopropanes1and2, and ofcis‐divinylcyclopropane3to give cycloheptadiene5have been determined. In addition it has been shown thattrans‐divinylcyclopropane‐cycloheptadiene rearrangements also occur under irradiation by a mercury lamp in benzene at 40°. These low‐temperaturein vitrorearrangements suggest that the biosynthesis of the cycloheptadienes inDictyopteris(dictyopterenes C′ and D′) may proceed by the sa

ISSN:0018-019X    

DOI:10.1002/hlca.19730560607

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe absolute configuration of (+)‐α‐ionone3(R), the absolute configurations at C(6) of (+)‐cis‐α‐irone5(6S) and (−)‐trans‐α‐irone6(6R), and the absolute configurations of (+)‐cis‐abscisic acid10(S) and (+)‐trans‐abscisic acid11(S) are

ISSN:0018-019X    

DOI:10.1002/hlca.19730560608

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractFuraneol®Registered trade mark ofFirmenich SA.[4‐hydroxy‐2,5‐dimethyl‐3(2H)‐furanone (1)], a flavour component of pineapple and strawberry, has been prepared by a two‐step synthesis starting with readily available 3‐hexyne‐2,5‐diol.By the same method 4‐hydroxy‐5‐methyl‐3(2H)‐furanone (2) and 2‐ethyl‐4‐hydroxy‐5‐methyl‐3(2H)‐furanone (3a) have been prepared from 2‐pentyne

ISSN:0018-019X    

DOI:10.1002/hlca.19730560609

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe acid catalysed dienone‐phenol rearrangement of methyl substitutedo‐propargyl‐cyclohexadienones (scheme 3) was investigated. The rearrangements were carried out in acetic anhydride containing about 10/00sulfuric acid. Under these conditions acetoxy benzenium ions are formed as intermediates. These then undergo charge‐controlled [3s, 4s]‐ and [1s,2s]‐sigmatropic rearrangements. Thus, the [3s,4s]‐process leads to the formation of the corresponding allenyl‐phenol acetates (19,21,23,25,28,30) whereas the [1s,2s]‐process yields propargyl‐phenol acetates (20,22,24,26,29), respect

ISSN:0018-019X    

DOI:10.1002/hlca.19730560610

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe catalytic hydrogenation of isoalloxazines in aqueous solutions proceeds non stoichiometrically.This is explained by a reaction side path, which is competitive with the normal reversible 1,5‐dihydrogenation and leads to the irreversible reduction of the ‘o‐xyloquinoid’ (rather than benzenoid) subnucleus in the (iso)alloxazine system. In trifluoroacetic acid, this irreversible side reaction is found to be complete within several hours, while 8 H‐equivalents are absorbed per flavin molecule. The products are shown to be cyclohexano‐[g]‐pteridine‐2,4‐diones in the normal 5,6,7,8‐tetrahydro state, which are oxidized to yield, subsequently, 7,8‐dihydro‐ and ‘fully oxidized’ pteridines (= 6,7,8,9‐tetrahydrofavins).The spectral characteristics, tautomeric structures and pK‐values are discussed in context with recent data on 6,7,8

ISSN:0018-019X    

DOI:10.1002/hlca.19730560611

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY