摘要:

AbstractThe crystal structure of the steroidal glycoside scillicyanosid‐pentahydrate has been determined byX‐ray analysis. The rings of the steroid backbone are A/Bcis, B/Ctrans, and C/Dcisfused, the six substituents are all in β‐position (5β‐D‐gluco‐pyranoside, 10β‐aldehyde, 13β‐methyl, 14β‐hydroxy, 16β‐acetoxy, and a 17β‐lactone ring). The crystal structure displays a complex system of hydrogen bonds between the five water molecules and the various oxygen functions in the steroidal glycoside. There are nointramolecular hydrogen bonds. 624 structural parameters were refined to anR‐value of 0.059 with 1907

ISSN:0018-019X    

DOI:10.1002/hlca.19730560702

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractAmong the eight species of the fern genusDryopteriswhich have been recorded from Kenya (East Africa), the group ofD. inacqualis, D. pentheriandD. schimperanais regarded as critical. There is no agreement among experts as to whetherD. inaequalis s. str. is restricted to South Africa and whether it should be separated specifically fromD. pentheriChemical and, as far as possible, cytological investigations of available material showed that the following taxa ofDryopterisoccur in Kenya (ploidy in brackets) : 1.D.athamantica(2 × );2.D.callolepis(4 × ); 3.D.inaequalis(4 × ); 4.D.kilenzensis(2 × ); 5.D.manniana(4 × ); 6.D.pentheri(2 × ); 7.D.schimperana(2 × ); 8.D.sp. RBF‐71/885 (TR‐330.5) (4 × ); 9.D.squamiseta(ploidy not determined). The nomenclature of the four critical taxa, 3, 6, 7 and 8 is provisional. For comparison, two taxa from the Canary Islands, 10. D. ‘dilatata’ (4 × ) and 11.D.oligodonta(2 × ) were also investigated.Among the nine taxa from Kcnya, two (4 and 9) did not contain any phloroglucides.Dryopteris kilomensismust be regarded as one of the few representatives of the genusDryopteriswhich lacks such compounds. On the other hand, the negative result for 9 is in agreement with the fact that this species has recently been transferred to a new genusNothopevanema.The following three new compounds havc been isolated: Trisaspidinol (8), fromD.inaequalis; Pentherin‐I (not quitc pure) and Pentherin‐I1 (hypothetical partial formula25), fromD.pentheri. Pentherin‐I is also present inD.sp. RBF‐71/885. Chemical and cytological results are compatiblc with the hypothesis that the latter is an allotetraploid derived from the diploids 6 and 7. The chemical patterns of 6, 7 and 8 show similarities to that ofD.manniana, which in turn also shows similarities to the EuropeanD.filix‐mas. Dryopteris ‘dilatata’ from the Canary Islands is chemically different from EuropcanD.dilatata s. str.in lacking para‐aspidin, while D. oligodonta gave results rather different from D. inaequalis or other East African species,

ISSN:0018-019X    

DOI:10.1002/hlca.19730560703

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractOn irradiation in the presence of dye sensitizers, vinylogous epoxy carbonyl compounds undergo a novel photofragmentation reaction, to give furyl ketones in good yields. The fragmentation process is probably preceded bytrans‐cisisomerization of the double bond; in one case thecis‐isomer could be isolated. In a side reaction epoxyenone10gives the cyclopentanone derivatives13and14by a [1, 2] shift of a methyl group.Similar dye sensitized photolysis of theendo‐peroxide2also gives the corresponding furyl ketone4, and the corresponding vinylogous epoxyketoneCis probably an intermediate in this transformation.The finding that dyes of relatively low triplet energies (∼ 30 kcal/mol) efficiently sensitize these reactions, and a certain wave length dependence suggest that the usual triplet mechanism cannot be i

ISSN:0018-019X    

DOI:10.1002/hlca.19730560704

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

Abstract3‐Chloro‐4,5‐dihydrofuran can be easily substituted in the 2‐position by metalation with butyllithium followed by treatment with an electrophilic reagent. The resulting derivatives may be dehalogenated to give compounds where the original ring structure is either retained or opened. In the latter case alk‐3‐yne‐1‐ols, and 1‐hydroxy‐4

ISSN:0018-019X    

DOI:10.1002/hlca.19730560705

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe PE.‐spectra of triacetylene1(3), methyldiacetylene2(2), dimethylacetylene3(1) and dimethyldiacetylene3(2) have been recorded. The π‐ionization potentials of the unsubstituted acetylenes can be parametrized in terms of a LCBO

ISSN:0018-019X    

DOI:10.1002/hlca.19730560706

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractThe equilibrium energetics and the kinetics ofcis‐transisomerization of some bis(dialkylsulfide)dihaloplatinum(II) complexes have been examined by1H‐NMR. spectroscopy. The isomers are stable in chloroform but each form isomerizes to an equilibrium mixture when free dialkylsulfide is added. Thecistotransprocess is endothermic and the position of the equilibrium is markedly dependent on the nature of the donor atoms and of the solvent. The rate of isomerization of Pt(Me2S)2Cl2is first order in complex and in Me2S. The isomerization proceeds by a double displacement mechanism as it is shown that the tris(dimethylsulfide)chloroplatinum(II) cation is an isolable intermediate of the reaction. When free Me2S is added totrans‐Pd(Me2S)2Cl2, isomerization does not occur and one observes instead a fast ligand exchange. Its mechanism is the usual associative one for substitutions in square planar d8comp

ISSN:0018-019X    

DOI:10.1002/hlca.19730560707

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractTo complete results presented in this and in previous papers of this series as well as published in patents of other authors a review is given on known and new variations of the heterocyclic moiety in GS 13005 type thio‐ and dithiophosphoric acid esters (1, 2) by modification of the 1,3,4‐thiadiazol‐2(3H)‐one ring5and by its replacement by analogue five‐ and homologue six‐membered rings.Among new esters of this type some containing the pyrazolinone ring3or a 2‐alkoxy‐4H, 6H‐1,3,4‐thiadiazin‐5‐one ring10(homologue of the original 5‐methoxy‐1,3,4‐thiadiazol‐2(3H)‐one ring in GS 13005) show no remarkable pesticidal activity, some others containing a pyrazolering 7 or a 3(2H)‐pyridazinonc ring8are moderately to highly active but toxic to inauinials in the same proportion.Attempts to prepare seven‐membered 2‐alkoxy‐ and 2‐alkylthio‐6,7‐dihydro‐l, 3,4‐thiadiazepin‐S(4H)‐ones11, Z‐rnethoxy‐l,3,4‐thiadiazepin‐S(4H)‐one12(ring vinylogue of the original 5‐methoxy‐l,3,4‐thiadIazol‐2(3H)‐one ring in GS 13005) and its 7‐methyl‐derivative have been unsuccessful due to unexpected side reactions, such as: five‐ring closure of 3‐(3‐chloropropionyl)‐thio‐ and ‐dithiocarbazic acid esters22to pyrazolidinone derivatives23, pyrazolinone ring closure of a 3‐(acetoacety1)‐thiocarbazic acid O‐methyl ester derivative26, bromine attack on sulfur in 3‐(2‐alkenoyl)‐thiocarbazic O‐methyl esters29instead of bromine addition at the double bond, and halogen splitting off without ring closure in 3‐(2,3‐dihalogeno‐alkanoyl) ‐thiocarba

ISSN:0018-019X    

DOI:10.1002/hlca.19730560708

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractBenzenediazonium tetrafluoroborate in 2,2,2‐trifluoroethanol decomposes to give fluorobenzene and phenyl 2,2,2‐trifluoroethyl ether. In the presence of benzene, toluene, trifluoromethyl‐benzene or anisole, the respective biphenyl derivatives are formed in addition to fluorobenzene and the ether. The distribution of the isomeric substituted biphenyls is consistent with an electrophilic substitution. No homolytic products (diazo tars, benzene) are formed. The reaction kinetics clearly show that ether formation and aryl‐dediazoniations are of second‐order type,i.e.that trifluoroethanol and the benzene derivatives mentioned above are rate‐determining factors. It is shown that these results exclude theSN1‐mechanism which is usually assumed for heterolytic dediazoniations;freearyl cations are therefore not involved in these reactions. AnSN2‐like mechanism seems to be the most likely, but one involving an encounter complex containing the dissociated benzenediazonium ion is also consistent with the ex

ISSN:0018-019X    

DOI:10.1002/hlca.19730560709

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractUsing an extraction procedure which permits determination of end‐points, the reduction of a number of tosylamino acids, their derivatives, and model compounds with sodium in liquid ammonia has been investigated. When the molecule contains a single acidic group in addition to the tosylamino group (as in the case of the simple mono‐tosylamino monocarboxylic acids) reduction proceeds with the consumption of 2 g‐at. Na per tosyl group and the formation of toluene‐4‐sulphinic acid. If the number of acidic groups in the products is insufficient to accommodate the number of electrons consumed in the reduction, the reduction of ionisable tosylamino groups is incomplete unless an acid is added. If the number of acidic groups is higher, or excess acid is added, the sulphur‐containing products include thiocresol and sulphite. This last reaction course is also observed whenever calcium is used in place of sodium. A partial interpretation of the results

ISSN:0018-019X    

DOI:10.1002/hlca.19730560710

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY

摘要:

AbstractA mechanistic and kinetic analysis of the photoreduction of 2‐phenylquinoxaline (I) to 3‐phenyl‐1,2‐dihydroquinoxaline (II) in the presence of alcohols and amines is described. It is concluded that the reduction in alcohols proceeds exclusivly over an excited singlet state I (S1), probably of mixed n‐π*, π‐π* configuration. The triplet state which is also populated (ϕ;isc= 0.62) shows π‐π* configuration but remains inactive. A calculated pKa* 6.2 of I (S1) by means of a.Förster‐cycle, makes a mechanism which includes a first step photoprotonation of I (S1), followed by formation of semiquinone type radicals very probable.In the presence of amines the formation of II proceeds exclusivelyviathe first excited triplet state of I. The calculated rate constants are strongly dependent on the solvent polarity and on the ionisation potentials of the amines. This demonstrates clearly the importance of a charge‐transfer mechanism. It is also shown that once the charge‐transfer from the amine to I (T1) has occurred, physical quenching by electron backtransfer is of no importance. At high amine concentration I

ISSN:0018-019X    

DOI:10.1002/hlca.19730560711

出版商:WILEY‐VCH Verlag GmbH    

年代:1973

数据来源: WILEY