摘要:

AbstractThe reactants, ion‐dipole complexes, transition states, and products for the proton transfer reactions HBCOH++ OCXH → HBCO ++HOCXH optimized at the SCF/4–31G* level of theory for B, X = F, Cl, H, CH3, CH2Cl, CHCl2and CCl3are studied. The intrinsic barrier ΔE*BXcorrelates with the degree of the O‐O bond contraction in the transition structure. Both intrinsic and overall barriers can be predicted with the aid of Marcus theory. Progressive degrees of chlorination of the alkyl group in B produce decreases in the barrier to proton transfer from HBCOH+to OCXH and increases in the reverse transfer barriers. These changes can be quantitatively reproduced by the Marcus equation for all

ISSN:0009-4536    

DOI:10.1002/jccs.199700070

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe nascent rotational distributions of MgH(X2σ+, v″ = 0, 1) resulting from the reaction of Mg(4s1S0) with H2and HD have been determined by using the laser pump‐probe technique. Like the case of Mg(1P1), the distributions appear to be bimodal which peak mainly at high N(26) with minor peaks at low N(6). There are no apparent differences when the escaping mass is doubled. The similarity between product rotational distributions from the 4S state and those from the 3P state, and no evidence of a kinematic isotope effect, reveal that a harpoon‐type mechanism may be operative. Our ab initio calculations reveal that in the entrance channel on the 31A1surface in C2vsymmetry or1σ+surface in C∞vsymmetry for 4S state, the reaction may lake place via a series of non‐adiabatic curve crossings with the ionic Mg+H2−pote

ISSN:0009-4536    

DOI:10.1002/jccs.199700071

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reactions of a new cationic complex, [Cp(CO)2Mo(η4‐2‐methyl‐3‐SPh‐C4H4)]+PF−6(3), with carbon, hydride, and nitrogen nucleophiles were found to give only the C‐1 addition products in good yield. The X‐ray crystal structures of two of the addition products4aand4econfirm the regio‐ and stereochemistry of the nucl

ISSN:0009-4536    

DOI:10.1002/jccs.199700072

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA series of caged 1,4‐diols,26, 29a/29b, 31, were synthesized from the Diels‐Alder cycloadduct21of 1,2,3,4‐tetrachloro‐5,5‐dimethoxycyclopentadiene and 1,4‐benzoquinone. Reduction of enedione21with aqueous TiCl3, followed by base‐catalyzed enolization in the presence of acetic anhydride, gave diene23b, which reacted with maleic anhydride and 1,4‐benzoquinone to produce the corresponding [4+2] cycloadducts24band27, respectively. The adduct24bwas converted to birdcaged 1,4‐diol26by photocyclization followed by decarboxylative olefination of resulted caged anhydride25b. The adduct27was photocyclized to cage compound28, which was aromatized to dihydroquinone29aby acid‐catalyzed enolization, or benzo‐annulated compound31by reduction and dehydration. The birdcaged 1,4‐diols26and31underwent fragmentation induced by (diacetoxyiodo)benzene to give enediones38/39and41/42, respectively. Photocyclization of38and39produced the corresponding caged compounds43and44, respectively, possessing homosecohexaprismane skeletons. The corresponding monohydrate43aof43was structurally characterized by single‐

ISSN:0009-4536    

DOI:10.1002/jccs.199700073

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPummerer‐type reaction intermediate2of methyl α‐(methylthio)acetate(1)has been found to react with 1‐alkenes to afford ene adducts3. Achillea amide5was synthesized from the ad

ISSN:0009-4536    

DOI:10.1002/jccs.199700074

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo novel hydrolysable tannins, potassium brevifolincarboxylate and acaindinin, together with eight known tannins—1‐O‐galloyl‐β‐D‐glucose, 1,2,3,6‐tetra‐D‐galloyl‐β‐D‐glucose, corilagin, geraniin, acetonylgeraniin A, euphormisin M2, repandusinic acid A, and chebulagic acid, as well as two flavonoid glycosides — quercetin 3‐O‐β‐D‐glucoside and rutin, were isolated fromAcalypha indica.Their structures were elucidated on the basis of

ISSN:0009-4536    

DOI:10.1002/jccs.199700075

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe asymmetric induction in the complexation reaction of (S)‐1‐methyl‐2‐(5‐methyl‐cyclohexa‐1,4‐dienylmethyloxy)‐pyrrolidine5and (S)‐2‐(2‐N,N‐dimethylamino‐1‐propanoxy)‐5‐methylcyclohexa‐1,4‐diene6having heteroatom adjacent the stereogenic center has been investigated. The diastereoselectivity was determined directly from the diastereotopic peaks in the1H NMR or by chemical correlation with9. The conversion of η‐1,4‐complexes7aand8ato9proceeded with high retention of configuration while that of the η‐2,5‐Fe(CO)3comp

ISSN:0009-4536    

DOI:10.1002/jccs.199700076

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe first total synthesis of 1,2‐Dehydronephthenol (15‐hydroxy‐cembra‐1,3,7,11‐tetraene), a novel cembranoid diterpene, was accomplished starting fromtrans, trans‐farnesol through seven steps in an overall yield of 17% by employing titanium‐induced intramolecular keto aldehyde reductive olefination‐coupling as the key macroc

ISSN:0009-4536    

DOI:10.1002/jccs.199700077

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe formation mechanism of Polyaniline was derived from the post reactions of the polymerization intermediate. The intermediate, RPAN, (3000 Å thickness film, purplish‐blue in color) was isolated on silane modified substrates after polymerization for 10 minutes. Under air, RPAN converts to emeraldine salt within a couple of seconds. In the inert atmosphere, the conversion occurred at a relatively low speed. In acidic media, the intermediate was believed to be a very reactive radical cation, which oxidized then coupled with aniline oligomers to start the auto‐catalytic chain growing process. When the radical cation was quenched in water or acid, a violet species, IPAN, with a structure composed mostly of pernigraniline units, was formed. IPAN reacts slowly with aniline oligomers in the presence of protons and oxidants to emeraldine. The conversion processes were monitored by IR and Uv/Vis/NIR spectros

ISSN:0009-4536    

DOI:10.1002/jccs.199700078

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractBenzyloxycarbonyl‐glutamylpeptidep‐nitrophenylesters were prepared from protected amino acids, e.g.:p‐nitrophenyl‐glutamate as carboxyl component and aminoacid or peptidep‐nitrophenylesters as amino components by different kinds of peptide coupling methods. Mixed carbonic anhydride and azide methods gave good results. Thep‐nitrophenylesters existed as temporary protecting groups, so the peptide couplings proceeded together with simultaneous activation. The conditions and applications of the procedure are discussed. The peptides having one or more active ester groups were used to form amides by their aminolysis with derivatives of ethylamine or were polycondensated (after deprotection) to obtain p

ISSN:0009-4536    

DOI:10.1002/jccs.199700079

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY