摘要:

AbstractThe reactions of 1,4,5‐trisubstituted imidazole 3‐oxides1a – kwith cyclobutanethiones5a,bin CHCl3at room temperature give imidazole‐2(3H)‐thiones9a – kin high yield. The second product formed in this reaction is 2,2,4,4‐tetramethylcyclobutane‐1,3‐dione (6a;Scheme 2). Similar reactions occur with1and adamantanethione (5c) as thiocarbonyl compound, as well as with 1,2,4‐triazole‐4‐oxide derivative10and5a(Scheme 3). A reaction mechanism by a two‐step formation of the formal cycloadduct of type7viazwitterion16is proposed inScheme 5. Spontaneous decomposition of7yields the products of this novel sulfur‐transfer reaction. The starting imidazole 3‐oxides are conveniently prepared by heating a mixture of 1,3,5‐trisubstituted hexahydro‐1,3,5‐triazines3andα‐(hydroxyimino) ketones2in EtOH (cf. Scheme 1). As demonstrated in the case of9d, a `one‐pot' procedure allows the preparation of9without isolation of the imidazole 3‐oxides1. The reaction of1cwith thioketene12leads to a mixture of four products (Scheme 4). The minor products,9cand the ketene15, result from an analogous sulfur‐transfer reaction (Path ainScheme 5), whereas the parent imidazole14and thiiranone13

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1585::AID-HLCA1585>3.0.CO;2-N

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractDeuterium‐labelled 5‐fluorocolumbianetin13was synthesized as a metabolic probe to examine the stereochemical course of the bioconversion of (+)‐columbianetin (12) into the angular furocoumarin angelicin (5). In leaves ofHeracleum mantegazzianum, oxidative dealkylation of the specifically deuterated fluorocolumbianetin13proceeded bysyn‐elimination of a D‐atom, from C(9), and the vicinal 1‐hydroxy‐1‐methylethyl substituent, yielding 5‐fluoroangelicin (23). This matches the stereochemical course of the related reaction converting (+)‐marmesin (10) into the linear furocoumarin psoralen (1). Key steps in the synthesis of 5‐fluorocolumbianetin (13) were the copper‐catalysed alkynylation/cyclization of 5‐fluoro‐8‐iodoumbelliferone(15) followed by a transfer hydrogenation, which established thecis‐orientation of the D‐Atom and the 1

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1596::AID-HLCA1596>3.0.CO;2-F

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractThe hexane extract from the leaves ofDasymaschalon sootepenseCraib(Annonaceae) showed strong cytotoxic activity against the L1210 tumor cell line. Activity‐directed fractionation of the extract by column chromatography on silica gel and high‐pressure liquid chromatography led to the isolation of the acetogenins1 – 4as the main active principles. The structures of the two novel structures named sootepensin A (1) and sootepensin B (2) were elucidated by spectroscopic analysis (UV, EI‐ and ESI‐MS, 1D‐ and 2D‐1H‐ and13C‐NMR). The absolute configurations were established by 2D‐NMR experiments utilizingMosheresters. Two recently described compounds, tonkinin C (3) and tonkinesin C (4), were also isolated and are new to the genusDasymaschalon. All four acetogenins were found to be highly cytotoxic against th

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1608::AID-HLCA1608>3.0.CO;2-F

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractThe cross‐metathesis of internal olefins is applied for the combinatorial synthesis of small organic molecules; this reaction is conveniently carried out in neat olefin (oleic‐acid derivatives) and requires only 0.001 equiv. of [Ru(CHPh)Cl2(PCy3)2] as catalyst (Cy = cy

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1616::AID-HLCA1616>3.0.CO;2-P

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractThe molecular structures of three PdIIcompounds are reported:a) the two [PdCl(Me)] complexes7aand8aeach containing a different chiral N,S‐chelate based on {[(dihydrooxazolyl)phenyl]methyl}‐thioglucose backbones,e.g., chloro({2‐[(4S)‐4,5‐dihydro‐4‐isopropyloxazol‐2‐yl‐κN]phenyl}methyl 2,3,4,6‐tetra‐O‐acetyl‐1‐(thio‐κS)‐β‐D‐glucopyranoside)methylpalladium(II) (7a) andb) one [Pd(η3‐C3H5)(P‐S)]+cation in which the P,S‐chelate stems from a phosphinoferrocene and thioephedrine‐derived thioether donor,i.e., [(S)‐1‐(diphenylphosphino‐κP)‐2‐((1R)‐1‐{[(1R,2S)‐1‐phenyl‐2‐(piperidin‐1‐yl)propyl]thio‐κS}ethyl)ferrocene] (η3‐prop‐2‐enyl)palladium trifluoromethanesulfonate (11). In the methylpalladium compounds7aand8athe thioglucose‐κSmoiety is pseudo‐axial (Figs. 2and3), whereas in the allyl complex, the thioephedrine‐κSmoiety is markedly pseudo‐equatorial (Fig. 5). It is suggested, based on these results,

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1622::AID-HLCA1622>3.0.CO;2-A

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractThe transformation of ethyl 3‐{[1‐(alkoxycarbonyl)‐2‐(dimethylamino)ethenyl]amino}2‐cyanoprop‐2‐enoates2to dialkyl 3‐aminopyrrole‐2,4‐dicarboxylates3in good

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1634::AID-HLCA1634>3.0.CO;2-X

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractDouble lithiation ofN‐[dimethyl(2‐thienyl)silyl]‐1,1‐dimethyl‐1‐(2‐thienyl)silanamine ((C4H3S)−SiMe2−N(H)−SiMe2−(C4H3S);1) leads,viaring opening of one thiophene moiety, to the title compound2([(C4H3S)−SiMe2−N(Li)−SiMe2−C≡C−CH=CH−SLi⋅OEt2]2) which is characterize

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1640::AID-HLCA1640>3.0.CO;2-I

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractThe NMR spectral analysis of voacangine hydroxyindolenine (2) and of some synthetic derivatives, together with mechanistic considerations, permitted to establish its absolute configuration at C(7) as (R). The configuration at C(7) in hydroxyindolenines of the ibogamine series is also discussed and would be (S).

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1645::AID-HLCA1645>3.0.CO;2-P

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractA H2O/MeOH extract of the pollen ofHippeastrumx hortorum (Amaryllidaceae) was analyzed. A mixture of different compounds (at the most 84) was found, namely the geometrically ((E,E), (E,Z), (Z,E), and (Z,Z) and structurally isomericN,N′‐dicoumaroyl (=N,N′‐bis[3‐(4‐hydroxyphenyl)prop‐2‐enoyl]),N,N′‐diferuloyl (=N,N′‐bis[3‐(4‐hydroxy‐3‐methoxyphenyl)prop‐2‐enoyl]),N,N′‐disinapoyl (=N,N′‐bis[3‐(4‐hydroxy‐3,5‐dimethoxyphenyl)prop‐2‐enoyl]),N‐coumaroyl‐N′‐feruloyl, andN‐feruloyl‐N′‐sinapoyl derivatives of spermidine (=4‐azaoctane‐1,8‐diamine=N‐(3‐aminopropyl)butane‐1,4‐diamine). Their structures were proven by using on‐line‐coupled high‐performance liquid chromatography and atmospheric‐pressure chemical‐ionization mass spectrometry (HPLC‐UV(DAD)/APCI‐MS and MS/MS), UV‐induced (E)⇌(Z) photoisomerization, and catalytic hydrogenation, as well by comparing their spectra and chromatographic behavior with those of synthetic standards. According to

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1654::AID-HLCA1654>3.0.CO;2-T

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY

摘要:

AbstractCycloadditions of 1‐methoxybuta‐1,3‐diene to (2R)‐N‐pyruvoyl and (2R)‐N‐(phenylglyoxyloyl)bornane‐10,2‐sultam ((−)‐1band (−)‐1c, resp.) under high‐pressure conditions are presented. The absolute configurations of the cycloadducts2b,cand of their resulting reduced alcohols3b,care based on their X‐ray analyses. The stereochemical course of these reactions is discussed and compared to the inverse diastereoselectivity observed for the analogous cycloaddition to (2R)‐N‐

ISSN:0018-019X    

DOI:10.1002/(SICI)1522-2675(19980909)81:9<1672::AID-HLCA1672>3.0.CO;2-0

出版商:Verlag Helvetica Chimica Acta    

年代:1998

数据来源: WILEY