摘要:

AbstractThe ionization energies of four [1,2,4,5]tetrazinodi(heteroarenes) ofC2hSymmetry have been measured by PE spectroscopy. It is found that the first ionization energy is very low (6.2 eV to 6.4 eV) and rather independent of the size and/or topology of the molecules. This is explained, by comparison with the results of a simple MO treatment, as being due to strong localization of the HOMO (ofAusymmetry) on the [1,2,4,5]tetrazino moiety of the molecules. The PE‐spectroscopic data are shown to be in agreement with the UV/VIS‐and electrochemical‐oxidation data published previ

ISSN:0018-019X    

DOI:10.1002/hlca.19870700702

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractPure (E)‐ or (Z)‐enoylsultams2were Oxidized with OsO4/N‐MethylmorpholineN‐oxide in a stereospecific and highly π‐face‐selective manner. Acetalization of the resulting 1,2‐diols furnished, after purification, the stable, crystalline acetals6in>99% d.e. and in 63–74% overall yield from2. Reductive or hydrolytic cleavage of6gave enantiomerically pure alcohols8or carboxylic acids9with recovery of the s

ISSN:0018-019X    

DOI:10.1002/hlca.19870700703

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractRacemic and enantiomerically pure methylN‐(tert‐butyl)‐N‐benzyl‐ andN‐1‐(phenylethyl)aziridinecarboxylates are prepared by known methods and converted to phenyl thioesters (1,2,15,16;Schemes 2 and 3). These are deprotonated with lithium diisopropylamide (LDA) and BuLi (for removal of diisopropylamine) in THF at dry‐ice temperature. The resulting lithiated species are surprisingly stable and are deuterated, alkylated (CH3, C2H5, allyl, benzyl), and added to aldehydes and nitroolefins in good yields (50–80 %, 18 examples;Schemes 1and4–6). The configurational stability of the lithiated species is studied, and conclusions about their structures are drawn. Thus, a C(α)‐lithiated ester (seeL,Scheme 9) or anO‐lithiated ‘enolate’ (seeM) with pyramidalized C(β)‐atom is proposed for the species from levorotatoryS‐phenylN‐benzylaziridinecarbothioate which does not undergo racemizati

ISSN:0018-019X    

DOI:10.1002/hlca.19870700704

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractTwo new 2H‐1‐benzopyranyl ketones1and2and three new pyrano[3,2‐c: 4,5,6‐d′e′]di[1]benzopyrandiyl diketones3,4a/4b, and5have been isolated from the leaves and twigs ofHypericum revolutumVAHL (Guttiferae). The structure of3(hyperevoline) was established by X‐ray analysis as 1,1′‐[1,13,13a,13b‐tetrahydro‐5,8,10‐trihydroxy‐2,2,6,9,13,13‐hexamethyl‐2H, 7aH‐pyrano[3,2‐c:4,5,6‐d′e′]di[1]benzopyran‐4, 11‐diyl]bis[2‐methyl‐1‐propanone]. The structures of the isolated compounds were established by spectroscopic (UV, IR, EI‐MS,1H‐ and13C‐NMR) and

ISSN:0018-019X    

DOI:10.1002/hlca.19870700705

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractIn the presence of HSO3F/Ac2O in CH2CL2, 2‐exo‐ and 2‐endo‐cyano‐5,6‐exo‐epoxy‐7‐oxabicyclo[2.2.1]hept‐2‐yl acetates (6a,b) gave products derived from the epoxide‐ring opening and a 1,2‐shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6‐exo‐epoxy‐7‐oxabicyclo[2.2.1]heptan‐2‐one (6c) gave 5‐oxo‐2‐oxabicyclo[2.2.1]heptane‐3,7‐diyl diacetates20and21arising from the 1,2‐shift of the acyl group. Acid treatment of 5,6‐exo‐epoxy‐2,2‐dimethoxy‐7‐oxabicyclo[2.2.1]heptane (6d) and of 5,6‐exo‐epoxy‐2,2‐bis(benzyloxy)‐7‐oxabicyclo[2.2.1]heptane (6e) gave minor products arising from epoxide‐ring opening and the 1,2‐shift of σ bond C(3)–C(4) and major products (25,29) arising from the 1,3‐shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6‐exo‐epoxy‐2,2‐ethylenedioxy‐7‐oxabicyclo[2.2.1]heptane (6f) gave 1,1‐(ethylenedioxy)‐2‐(2‐furyl)ethyl acetate (32, major) and a minor product33, arising from the 1,2‐shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2‐shifts toward electron‐deficient centers has been established: acyl>alkyl>alkyl α‐substituted with inductive electron‐withdrawing groups. This order is valid for compe

ISSN:0018-019X    

DOI:10.1002/hlca.19870700706

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractSynthesis of the optical isomers of (±)‐methyl 6,7‐dimethyl‐3′,4′‐dideoxynorlaudanosoline‐1‐carboxylate ((±)‐2) was accomplished by reaction of (±)‐2with (+)‐(R)‐1‐phenylethyl isocyanate, separation of the urea diastereoisomers (−)‐4Aand (+)‐4B, and alcoholysis of the ureas in refluxing BuOH. Optically active isoquinoline‐carboxylates2A,Band hydantoins8A,Bisolated were characterized. The absolute configuration of the reaction products was established by X‐ray analysis of the optically active hydantoin (+)‐8A. Hydrolysis of the methyl isoquinolinecarboxylates2A,Bwith 48% HBr soln. at reflux afforded the desired optically active 3′,4′‐dideoxynorlaudanosoline‐1‐carboxylic acids1A,Brequired for enzyme‐inhibition studies. Details of the X‐ray diffraction analysis of (+)‐methyl salsoline‐1‐carboxylate hydrobromide ((+)‐11A·HBr) prepared earlier are included. CD spectra of (+)‐(S)‐methyl 6,7‐dimethyl‐3′,4′‐dideoxynorlaudanosoline‐1‐carboxylate hydrobromide ((+)‐2A. HBr) and (−)‐(R)‐methyl salsoline‐1‐carboxylate hydrochlor

ISSN:0018-019X    

DOI:10.1002/hlca.19870700707

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractThe intramolecularDiels‐Alderreaction conducted with acetylenic acylureas, obtained from carbodiimides, and the acetylenic acid5and its derivatives13gave the 1,2‐annellated barrelene14(from13a) and the benzobarrelenes8(from5) and15(from13b); in the case of 3‐butynoic acid (1),[1,3]‐H shift were observed. The formation of the azabarrelenes16(from13c) as an intermediate is postulated which looses HCN to afford the indolinone17. The acylureas6and9underwent isocyanate cleavage instead of [4+2] cycl

ISSN:0018-019X    

DOI:10.1002/hlca.19870700708

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractThe ‘active’ dimer hydroxide, [Cr2(μ‐OH)2(OH)4(OH2)4]·2 H2O, has been characterised by means of IR spectroscopy, thermal analysis, X‐ray powder diffraction, and electron microscopy. Thermogravimetric measurements and the Cr content of the hydroxide are in agreement with this composition. The IR spectrum supports the notion that this hydroxide is composed of unaltered dimer fragments linked through hydrogen bonds ofca.2.8 Å. The compound is microcrystalline in nature with an X‐ray powder diffraction pattern distinctly different from that of the isomeric ‘active’ monomer hydroxide. Electron micrographs of the ‘active’ dimer hydroxide indicate that this material consists of platelets the sie of which is dependent on the

ISSN:0018-019X    

DOI:10.1002/hlca.19870700709

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

AbstractThe novel reagents formed by combination ofGrignardreagents (RMgX) with lithium diisopropylamide (LDA) convert non‐enolizable or slowly enolizable carboxylic esters or caboxamides into ketones which are protected from further reaction by theirin situconversion into enolates. These enolates can be trapped with electrophiles such as Me3SiCl and allyl bromide. The scope of thisGrignardmono‐addition is illustrated by two direct syntheses of artemisia ketone (

ISSN:0018-019X    

DOI:10.1002/hlca.19870700710

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY

摘要:

New Aromadendrane Derivatives from Tolu BalsamFive new aromadendrane derivatives were isolated from tolu balsam by HPLC and their structures elucidated by NMR spectroscopy.

ISSN:0018-019X    

DOI:10.1002/hlca.19870700711

出版商:WILEY‐VCH Verlag GmbH    

年代:1987

数据来源: WILEY