摘要:

AbstractBare Fe(I) cations act in the gas phase as dehydrosulfurization catalysts for butyl isothiocyanate by specifically coupling the S‐atom with remote H‐atoms from the ω and (ω − l) position of the alkyl chain. Other losses induced by Fe(I) are due to ‘remote functionalization’, the formation of ion/dipole intermediates, and insertion/β‐hydrogen s

ISSN:0018-019X    

DOI:10.1002/hlca.19900730202

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAs a direct test of theCane‐Westleyhypothesis concerning the mode of assembly of ether rings in the polyether class of ionophore antibiotics, we describe experiments culminating in the synthesis of three putative intermediates on the monensin biosynthetic pathway and incorporation experiments with these materials and the monensin‐producing organismStreptomyces cinnamonensis. The putative intermediates synthesised include the trienes [21‐3H]‐7and [13‐3H]‐10, and the diene [9‐3H]‐11. The results of the incorporation experiments conducted with whole cell cultures suggest that [13‐3H]‐10and [21‐3H]‐7are unable to cross the intact cell membrane ofS. cinnamonensis, whereas diene [9‐3H]‐11can gain entry to the cellular interior, but is then degraded efficiently, most likely by a pathway closely related to β‐oxidation, without being specifically in

ISSN:0018-019X    

DOI:10.1002/hlca.19900730203

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe ability of the monensin‐producing organismStreptomyces cinnamonensisto bioconvert the (E)‐and (Z)‐isomers of nerolidol (= 3,7,1 1‐trimethyldodeca‐1,6,10‐trien‐3‐ol) into new oxygenated products has been investigated. When a3H‐labelled racemic form of each sesquiterpene was added to fermentations ofS. cinnamonensis, several new3H‐labelled products could be detected. Two products were isolated from bioconversion of (E)‐nerolidol, the amide8and the9(Scheme 2), whereas four products were isolated from the bioconversion of (Z)‐nerolidol, the epoxydiol10, triols11and12, and the tetrahydrofuryl alcohol13(Scheme 4). Products9–13were obtained as a 1 : 1 mixture of diastereoisomers, and12was shown to arise by the overallantiaddition of two OH groups to the trisubstituted (Z)‐double bond of (Z)‐nerolidol. Both isomers of nerolidol as well as the acetylene7are inhibitors of monensin production in shak

ISSN:0018-019X    

DOI:10.1002/hlca.19900730204

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractWith ω‐halogenoalkyl isocyanates, 2‐oxocyclododecane‐l‐carbonitrile is transformed under ring enlargement to 1‐(ω‐halogenoalkyl)‐2,14‐dioxo‐1‐azacyclotetradecane‐3‐carbonitriles. In the presence of base, these products undergoO‐ orC‐alkylation leading to bicyclic compounds. TheC‐alkylation product 7 undergoes solvolysis to form a

ISSN:0018-019X    

DOI:10.1002/hlca.19900730205

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractIt is shown that the nudibranch molluscArmina maculataand its prey, the pennatulacean octocoralVeretillum cynomorium, of east Pyrenean waters contain a novel cembranoid, preverecynarmin ((+)‐8), besides the known cembranoid cembrene C (9) and three further briarane diterpenoids (verecynarmin E ((−)‐5), F ((−)‐6), and G ((−)‐7)). A biogenetic schem

ISSN:0018-019X    

DOI:10.1002/hlca.19900730206

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe platinum(0) complexes [Pt(C2H4)(PP)] (PP = 1,2‐bis[(diphenylphosphino)methyl]benzene (2) and (+)‐DIOP = (+)‐1,4‐bis(diphenylphosphino)‐1,4‐dideoxy‐2,3‐O‐isopropyliden‐D‐threitol), when promoted by CH3SO3H, become active catalysts for styrene hydroformylation with total yields of aldehydes ranging from 44 to 67% und selectivities towards 3‐phenylpropanal ranging from 80 to 88%. Smaller amounts of the corresponding alcohols (3–18%) are also obtained with a selectivity towards 3‐phenylpropanol of 94–96%. When DIOP complexes were used, no stereoselectivity for asymmetric

ISSN:0018-019X    

DOI:10.1002/hlca.19900730207

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of substituents (X  H, Me, or F at C(6), R  H or Me at C(2′) of the allyl side chain) on the photoisomerization (λ = 350 nm) of 6‐allylcyclohex‐2‐enones1in MeCN is studied. Substituents X control the overall efficiency of intramolecular [2 + 2] photocycloadduct formation (Φ: Me>F>H) but do not exercise an influence on the orientation of addition of the exocyclic double bond to the enone CC bond. In contrast, replacement of the prop‐2‐enyl (R  H) by a 2‐methylprop‐2‐enyl (R  Me) side chain causes a change in the tricyclo[3.3.1.02,7]nonan‐6‐one4vs.tricyclo[4.2,1.03,8]nonan‐7‐one (5) product ratio from 100:0 (R  H) to roughly 2:1 (R  Me) but has almost no bearing on the relative rates of conversion of1to products. For C(6)‐unsubstituted enones1aaand1ba(X  H), the efficiency of cyclization becomes low enough so that lumiketone rearrangement to bicyclohexanones6and 3‐isopropylcyclopent‐2‐enones9becomes competitive. Enones9undergo consecutive intramolecular [2 + 2] photocycloaddition to tricyclo[3.2.1.03,6]octan‐2‐ones7and to tricyclo[3.2.1.03,6

ISSN:0018-019X    

DOI:10.1002/hlca.19900730208

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractBiomimetic syntheses of racemic aristomakinine ((±)‐3) and aristomakine ((±)‐4), an unusual indole alkaloid bearing anN‐isopropyl group, are described. The key step is aGrob‐type fragmentation ofanti‐15‐aristotelinyl methanesulfonate ((±)‐2) to the intermediate iminium ionIwhich, upon subsequent hydrolysis, furnished aristomakinine ((±)‐3). On the other hand, the same intermediate could be reducedin situto aristomakine ((±)‐4). The controversial relative configurations of the two alkaloids have been firmly established by means of NOE

ISSN:0018-019X    

DOI:10.1002/hlca.19900730209

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

Substituent, Heteroatom, and Solvent Effects on the Thermal‐Bleaching Kinetics and Absorption Spectra of Photomerocyanines Issued from Spiro[indoline‐oxazines]Quantitative information useful for the development of new photochromic systems is obtained from the study of heteroatom and substituent effects on the thermal‐bleaching kinetics and the absorption spectra of the photomerocyanines issued from spiro[indoline‐oxazines]. The effect on photochromic properties of the presence of N‐atoms either in the dimethine bridge or in the aromatic rings has been investigated through the comparison of spiro[indoline‐naphthopyrans]Cwith spiro[indoline‐naphthoxazines]Aand with spiro[indoline‐quinolinoxazines]B. Besides the occurrence of biexponential thermal‐bleaching kinetics in non‐polar solvents is observed: a tentative explanation for this observation is given which involves the formation, in either sequential or parallel steps, of energetically distinct stereoisomers

ISSN:0018-019X    

DOI:10.1002/hlca.19900730210

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis of 8‐aza‐1,3‐dideaza‐2′‐deoxyadenosine (3a) as well as of 4‐ and 5,6‐substituted benzotriazole 2′‐deoxy‐β‐D‐ribonucleosides is described (Schemes 1–3). Glycosylation of benzotriazole anions is stereoselective in all cases (exclusive β‐D‐anomer formation), but regioisomericN1,N2, andN3‐(2′‐deoxyribofuranosides) are formed. The distribution of the regioisomers is controlled by the nucleobase substituents. Anomeric configuration as well as the position of glycosylation are determined by UV and NMR in combination with 1D‐NOE‐difference spectroscopy. The unprotonated forms of 4‐aminobenzotriazoic 2′‐deoxy

ISSN:0018-019X    

DOI:10.1002/hlca.19900730211

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY