摘要:

AbstractA convenient method is described for the synthesis of γ‐lactams from various imido‐propellanes via the thio derivatives by desulfurization with tribulyltin hydride. Diels‐Alder reactions between thioimido‐, lactamo‐, and imido‐propellanes with methyl triazolinedione

ISSN:0021-2148    

DOI:10.1002/ijch.198900037

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPhotosensitized regeneration of NAD(P)H cofactors is accomplished by biocatalyzed and artificially catalyzed transformations in photochemical assemblies. PhotogeneratedN,N'‐dimethyl‐4,4′‐bipyridinium radical cation, MV+., acts as electron carrier for the reduction of NADPH in the presence of the enzyme ferredoxin reductase and for the reduction of NADH in the presence of lipoamide dehydrogenase. For the photogeneration of MV+.and subsequent NADPH formation, three different photosensitizers are applied: Ru(bpz)23+, Ru(bpy)23+, and Zn—TMPyP4+. The highest quantum yield for NADPH formation is observed with Ru(bpz)32+and is ϕ = 1.7 × 10−1. For NADH regeneration only Zn‐TMPyP4+can be applied. Ru(bpy)32+and Ru(bpz)2+3interact with NADH in their excited or oxidized forms and therefore cannot be used as light‐active compounds in the system. The NADPH regeneration cycle has been coupled to the biocatalyzed synthesis of glutamic acid. Although Ru(bpz)32+is 42.5‐fold more efficient than Ru(bpy)32+in the regeneration of NADPH, the synthesis of glutamic acid is improved only by a factor of 2 in the presence of Ru(bpz)32+, implying that the coupled process is rate limiting. Oxidative regeneration of the NAD+cofactor is accomplished in a photosystem that includes Ru(bpy)32+as photosensitizer. The photoprocess is coupled to dehydrogenation of ethanol, propanol, lactic acid, and alanine with concomitant H2evolution. A photosystem that includes Ru(bpy)32+as photosensitizer, ascorbate as electron donor, and chloro‐tris‐(3‐diphenylphosphinobenzene sulfonate)Rh(I), RhCl(dpm)33‐, is catalytically active in the photoinduced regeneration of NAD(P)H cofactors. Mechanistic investigations show that photogenerated Ru(bpy)3+mediates the generation of a hydrido‐rhodium complex that acts as a charge relay

ISSN:0021-2148    

DOI:10.1002/ijch.198900038

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe mechanism of intramolecular [2 + 2] photocycloaddition of1bhas been investigated. Structure determination of deuterium‐labeled photoadducts was accomplished by2H NM

ISSN:0021-2148    

DOI:10.1002/ijch.198900039

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractReaction of dichlorovinylene carbonate with 1,6‐methano[10]annulene (2) followed by hydrolysis of the intermediate adduct afforded α‐diketone3. Photolysis of3at liquid nitrogen temperature yielded the title compound,1. The activation parameters for the thermal isomerization1 → 2wereΔH+= 5.1 kcal/mole andΔS−= −19 eu (100 K). The structure of3was established by X‐ray analysis. This analysis and MM2 calculations on a number of related compounds provide additional examples of the so‐called “Klammer” e

ISSN:0021-2148    

DOI:10.1002/ijch.198900040

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractContrary to common preconceptions, orbital correlation diagrams can be useful for deducing the mechanism and stereochemistry of degenerate sigmatropic rearrangements. The correlation lines have to be drawn between the reactant and the postulated transition state, rather than between the homomeric reactant and product. In the case of the Cope rearrangment, this is done most economically withOrbital Correspondence Analysis in Maximum Symmetry(OCAMS), by drawing correspondence lines between molecular orbitals of the reactant and those of a formal superposition (STS) of alternative transition structures (TS) in a symmetry point group that includes those of both as subgroups. The alternativeboat(C2v) andchair(C2h) transition structures postulated for the degenerate Cope rearrangement of 1,5‐hexadiene are formally combined to an STS of D2hsymmetry. OCAMS then selects its C2hcomponent, indicating that the pathway via thechair‐liketransition state is preferred, in agreement with experimental and computational results for both the Cope rearrangement and the isoelectronic Claisen rearrangement. Rearrangement through the less favoredboatpathway is shown to arise from a changed electronic configuration in the transition state. Computational evidence is presented showing that the unexpectedly facile rearrangement of polycyclic molecules like semibullvalene and barbaralane, which are constrained to react via theboatpathway, is primarily due to steric and stereoelectronic factors that are explicable in molecular orbital terms, rather than to the incursion of a biradicaloid transition st

ISSN:0021-2148    

DOI:10.1002/ijch.198900041

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe steric course of an azidolytic SE'desilylation of a chiral allyl silane and experiments on electrophilic alkylations of ketene‐O,N‐acetals are described. In this context, we point to some merits of combining qualitative concepts of σ‐conjugation with the ẗ‐bond model of do

ISSN:0021-2148    

DOI:10.1002/ijch.198900042

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.198900016

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY