摘要:

Synthesis of [1,2,4]Triazolo[1,5‐a]quinazolines. Assignment of the Conformation of Substituents with the Aid of13C‐NMR. SpectroscopyThe synthesis of [1,2,4]triazolo[1,5‐a]quinazolines by condensation of 2‐hydrazinobenzoic acid withN‐cyano‐imidates is reported. The preferred conformation of substituents at C (5),e.g.N (CH3)2, N (CH3)NH2, N (CH3)OH, relative to the aromatic system is deduced with the aid of13C‐NMR. chemical shifts and proton nuclearOverhausereffec

ISSN:0018-019X    

DOI:10.1002/hlca.19800630102

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

Synthesis of (‐)‐(R)‐4‐Hydroxy‐β‐ionone and (‐)‐(5R, 6S)‐5‐Hydroxy‐4,5‐dihydro‐α‐ionone aus (‐)‐(S)‐α‐IononeThe absolute configuration of the chiral 4‐hydroxy‐β‐ionones and 5‐hydroxy‐4,5‐dihydro‐α‐ionones has been determined by chemical connection with (‐)‐(S)‐α‐iononei.e.by stereoselective epoxidation of the latter, followed by base cat

ISSN:0018-019X    

DOI:10.1002/hlca.19800630103

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

Regioselective Oxidations, Regioselective Halogenations and Carbene Reactions of Sugar Derivatives Bearing a Thioether GroupRegioselective stoechiometrically controlled procedures are described for the oxidation of thiosugars either at the sulfur atom (to sulfoxides or sulfones) or at a hydroxymethylene group (to ketosugars). Ruthenium tetraoxide reacted at both sites. Chloration (SO2Cl2) of β‐ketothioether sugar derivative3took place exclusively at C(6). Evidence is given that a chlorosulfonium intermediateCwas formed when the dichloroketothiosugar derivative6was treated with SO2Cl2. The carbene generated from the tosylhydrazone16rearranged to the enoses17–20, the migrating group coming in equal proportions from C(4) and C(6). Some stereochemical aspects of these reactions are discu

ISSN:0018-019X    

DOI:10.1002/hlca.19800630104

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe impetus for this work was the structure of a trinuclear complex with two carbonyl groups showing incipient triple bridging ‐ Cp2Rh3(CO)4−. Its structure, barrier to rotation of one Rh(CO)2−piecevs.the rest of the molecule, and the nature of the bridging carbonyl interaction are analyzed. Isolobal analogies form an interesting connection between this complex and a bridged isomer of the recently synthesized carbene complexes, Cp2Rh2(CO)2CR2, one isomer of Cp2Rh3(CO)3, and hypothetical carbyne complexes Cp2Rh2(CO)2CH+,−. A general bonding model for Cp2Rh2(μ‐CO)2X complexes is constructed. The model, rich in geometrical detail, allows minima for the bridging carbonyl groups bending toward and away from the bonde

ISSN:0018-019X    

DOI:10.1002/hlca.19800630105

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C‐NMR. spectra of a number of colchicine derivatives are given comprising examples of the normal series (4→10), iso series (11→16) and colchicine series (17), which were either reported in the literature or obtained by partial synthesis or degradation reactions. The13C‐NMR. assignments were made by comparisons with known compounds and selective single‐frequency offresonance decoupling experiments. Selective proton decoupling experiments have also allowed assignments of theH—C(11) andH—C(12) protons of the iso and colc

ISSN:0018-019X    

DOI:10.1002/hlca.19800630106

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractpKaValues of 42 quinuclidinium perchlorates I have been measured in 0.1Maqueous KCl‐solution. In a few cases small corrections of earlier thermodynamic pKavalues are indicated. These measurements, in conjunction with recent X‐ray structure determinations, confirm the reliability of the inductive substituent constants σIqderived from

ISSN:0018-019X    

DOI:10.1002/hlca.19800630107

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractThe overall kinetic solvent isotope effects on the acid catalyzed hydrolysis of a series of 2‐aryl‐2‐diazocarboxylic esters ArCN2COOCH3, and one 2‐aryl‐2‐diazocarboxamide C6H5CH2CON (CH3)2vary inversely with the reactivity of the substrate, between limits of 3.14 and 1.46. A linearHammettplot for the hydrolysis rates of thea‐diazocarboxylic esters indicates that there is no mechanistic change for the hydronium‐ion‐catalyzed reaction. The relation between hydrolysis rate and buffer acid concentration deviates from linearity for high values of the latter. It is shown on the basis of the solvent isotope effects for the non‐linear region that this deviation does not stem from a mechanistic change caused by the buffer base component. The specific salt effects on the general acid‐catalyzed r

ISSN:0018-019X    

DOI:10.1002/hlca.19800630108

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractA novel class of odorants is described where the odor is associated with the interaction of two functional groups, one being an H‐donor (AH function), and the other anH‐acceptor (Bfunction). Generally, odor occurs only if the distance between the two structural elements (AH/B system) is less than 3 Å. Bifunctional derivatives of thep‐menthane and iridane series served as models for deriving this rule. The stereospecificity of odor perception was an important prerequisite for its establi

ISSN:0018-019X    

DOI:10.1002/hlca.19800630109

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

AbstractStructures of Six Coleons (Diterpenoids) fromSolenostemon monostachys(P. BEAUV.) BRIQ. (Labiatae)The above mentioned African labiate has been investigated for its leaf‐gland pigments. Besides the already known coleons C (1) and H (2), 2a‐formoxy‐coleon C (3), 12β‐O‐acetyl‐coleonZ(7), 12β‐O‐acetyl‐7‐O‐formyl‐7‐O‐desacetyl‐coleonZ(8) and a not separated mixture of 17‐acetoxy‐12β‐O‐acetyl‐coleonZ(9a) and 12β‐O‐a

ISSN:0018-019X    

DOI:10.1002/hlca.19800630110

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY

摘要:

Nucleophilic Aminoalkylation with ThiopivalamidesVorläufige Mitt. [1].Of the twelve thioamides7a‐eand8a‐g, onlyN,N‐dimethylthiopivalamide (7a) could be metallated at the CH‐group ina‐position to the N‐Atom. The reagent9thus obtained(Table 1)reacts in high yields with primary haloalkanes, with aldehydes, and with non‐enolizable ketones(Table 2). As shown inScheme 1, the products can be hydrolyzed to pivalamides, cleaved to secondary amines, or reduced to neopentylamines (see18/19, 15/equation (4) and (5), and16/20,

ISSN:0018-019X    

DOI:10.1002/hlca.19800630111

出版商:WILEY‐VCH Verlag GmbH    

年代:1980

数据来源: WILEY