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Graphical Abstract (Angew. Chem. Int. Ed. Engl. 71997)

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COVER PICTURE
The cover picture shows the crystal structure of [U(C,Me,),], the first Sf-element
compound of this type. Previously, formation of tris(pentamethylcyclopentadieny1)
complexes was limited to samarium since the only available syntheses required the
special chemistry of samarium(I1) precursors. Now it is possible to make these
molecules from trivalent metal hydrides and tetramethylfulvalene. This new synthetic method should open up the area of [M(C,Me,),] chemistry so that the unusual
reactivity of these sterically crowded molecules can be explored. The structural
diagram (generated by Michael Greci with the program Spartan 4.1.1 from Wavefunction) is superimposed on a picture of a crystal of the samarium compound
[Sm(C,Me,),], which was taken inside a specially modified Vacuum/Atmospheres
glovebox by using a Panasonic videomicroscope, a McBain fiber-optic light pipe,
and a Minolta Snappy video capture device. More details on the chemistry of
[U(C5MeS),]are reported by W. J. Evans et al. on pages 774ff.
REVIEWS
Contents
4-
Known for nearly two centuries, yet hardly researched! The rich chemistry of xanthates leaves
much to be discovered. Xanthates are cheap precursors to a great variety of radicals that can be efficiently
captured
in reactions
free of heavy
metals.
S-propargyl
xanthates
also undergo
thermal
con-
S. Z. Zard* ................................
On the Trail of Xanthates: Some New
Chemistry from an Old Functional Group
R
version into betaines of a novel type that are at the
center of a host of nonradical transformations as
diverse as diene formation and inversion of the configuration of secondary alcohols.
R'
Rotatable or not rotatable? The rotation of the XH group about the M-C 0-bond
makes a considerable contribution to the activation energy of the conversions of 2
into carbene complexes of electron-deficient transition metals such as 1 and into the
highly reactive titanaallenes 3. The multitude of reactions that 3 can undergo has
increased knowledge of the chemistry of these electron-deficient transition metal
complexes, which in turn has led to new discoveries about the reactivity of the alkyl
and alkenyl derivatives 2 as well as of various metallacycles of titanium group
metals.
[L,Ti=CR,]
1
(X: CR,)
R-H
L,T;>\'h
R '
2
(X: C=CH,)
- R-H
-
R. Beckhaus* ............................
686-713
Carbenoid Complexes of Electron-Deficient Transition Metals-Syntheses of and
with Short-Lived Building Blocks
[L,,Ti=C=CH,l
3
HIGHLIGHTS
a
+J
Antitumor agents possibly better than
4..
taxol might be derived from the
epothilones (depicted on the right),
/ '4..
..\\OH
which likewise bind to microtubules.
The epothilones, which were discov0
ered by Hofle et al. and Reichenbach
epothilone A: R = H
epothilone 6: R=Me
0
OH
0
etal., are easier to synthesize and
more soluble in polar solvents than
taxol. The results ofin vivo activity studies are now eagerly awaited. The exceptional
importance of these new tubulin stabilizers is reflected in the race for synthetic
approaches to these compounds that has already led to the first total syntheses and
several partial solutions.
.._
Molecular beams with the carrier gas
>..<a
%-(P
argon contain prereactive complexes
!. ,..i..-.of halogens and interhalogens with
._..
NH,, H,O, and H,S, as detected by
H
..__
Fourier-transform microwave spectroscopy; the structures have been elucidated. The partial structures of NH,, H,O,
and H,S as well as F,, C1F (cf. picture), Cl,, BrC1, and Br, are almost the same for
the complexes as for the free molecules. The weak complex bonds result from
electrostatic forces.
__I
664
672-685
Q VCH Verlagsgeselkhaft mbH, 0-69451 Weinheim. 1997
Contents
L. Wessjohann* .........................
715-718
Epothilones: Promising Natural Products
with Taxol-Like Activity
H. Burger* ................................
718-721
Gas-Phase Complexes : Possible Prereactive
Gateways for Reactions of Halogens with
NH,, H,O, and H,S
OS7o-0833j97136n7-0664 S 1 7 . S O i S O j O
Angen. Chem. Inl. Ed. Engl. 1997, 36, No. 7
Enzyme preparations that are stable in organic solvents and in aqueous media can be
obtained by covalently cross-linking enzyme crystals. The resulting exceptionally
stable biocatalysts, the “cross-linked enzyme crystals” (CLECs), efficiently catalyze
enzymatic peptide syntheses (see example below), esterfications, hydrolyses, C -C
bond-forming reactions, and reductions. Z = benzyloxycarbonyl.
T. Zelinski, H. Waldmann* _._....722-724
Cross-Linked Enzyme Crystals (CLECs):
Efficient and Stable Biocatalysts for
Preparative Organic Chemistry
A
A
themolysin-CLEC
Z ” N A N
OMe
ZHN
0
ethyl acetate
19 cycles,20 h each, 55°C
‘COOH
COMMUNlCATlONS
A noninvasive means to map biological structure is offered by magnetic resonance
imaging (MRI). A new class of MRI contrast agents is described where the relaxivity
of the complex is modified by the activity of a specific enzyme (/I-galactosidase,
[Eq. (a)]). This type of agent offers the promise of direct three-dimensional visualization of gene expression in the form of an acquired MR image.
R. A. Moats, S. E. Fraser,
T. J. Meade+ ..............................
Ringing a peptide (not-so-dumb)bell: the amide groups in the glycylglycine derivative
shown below provide the information required to template the formation of benzylic
amide macrocycles to yield peptide [2]rotaxanes. The four key hydrogen bonds
responsible for cyclization remain intact in the rotaxane in nonpolar solvents, in the
solid state, and (when X = N) even in polar solvents such as [DJDMSO and
[D,]DMSO/D,O mixtures. X = CH, N ; shaded sphere = Ph,CH, black sphere =
Ph,CHCH,.
D. A. Leigh,* A. Murphy, J. P. Smart,
A. M. Z. Slawin _._.......__._.._._.__.__
728-732
Thirty-six peripheral glucopyranosidic units are
placed in the higher generation dendrimer prepared
by a convergent growth strategy from dendimer
wedges and an acid core (see schematic drawing on
right). These compounds permit a novel entry into
hitherto unknown neoglycoconjugate systems,
which can be used for studying carbohydrateprotein interactions.
Angew Chem Int Ed Engl 1997. 36, No 7
$2) VCH Verlagsgesellschaft mbH, 0-69451 Wernherm, 1997
726-728
A “Smart” Magnetic Resonance Imaging
Agent That Reports on Specific Enzymatic
Activity
Glycylglycine Rotaxanes-The Hydrogen
Bond Directed Assembly of Synthetic
Peptide Rotaxanes
P. R. Ashton, S. E. Boyd,
C. L. Brown, N. Jayaraman,
J. F. Stoddart* _.._._.._._._...._.._._.__.
732-735
A Convergent Synthesis of a CarbohydrateContaining Dendrimer
087O-0833/97~3607-0665~17.80+
SOjO
665
Contents
The concurrent operation of two distinct hydrogen-bonding motifs, namely the carboxyl dimer supramolecular synthon (dashed lines represent
hydrogen bonds) and the threading
of two secondary dialkylammonium
cations (black bars) through the cavity of the ditopic macrocyclic polyether bis-p-phenylene[34]crown-l0 (rectangular boxes) leads to unique superstructures. The macrocyclic polyether enforces supramolecular preorganization of the
carboxyl groups, permitting formation of novel doubly encircled supermolecules
and interwoven supramolecular arrays in the solid state (the diagram shows a
schematic representation).
Butterflylike frameworks are present in the isostructural clusters 1 and 2, in which the
chalcogen atom is bound as a pg ligand to Co and Sn. These complexes are formed
by Se/Te addition to the unbridged Co-Sn bond of 3 at room temperature. Compounds 1 and 2 are the first defined molecular complex compounds that contain the
typical semiconductor combination Sn/E (E = Se, Te) and a ferromagnetic metal,
and thus they could be of interest for applications in materials science.
E=Sel,Te2
Homogenous catalysis as long as it is
needed: the advantages of homogeneous and heterogeneous metal
catalysis can be combined by attachment of an alkaloid ligand to polyethyleneglycol methylmonoether.
Diols with up to 99% ee have been
obtained in the asymmetric Sharpless
dihydroxylation of olefins with the
polymer modified ligand 1 (DHQD =
dihydroquinidine) .
P. R. Ashton, A. N. Collins,
M. C. T. Fyfe, S. Menzer,
J. F. Stoddart,*
D. J. Williams ............................
735-739
Supramolecular Weaving
J. J. Schneider,* J. Hagen, D. Blaser,
R. Boese, C. Kruger ......_...._...._.
739-741
The Reactivity of the Unbridged Co-Sn
Bond in [(q5-C5H,)(q2-C,H,)Co-Sn{CH[Si(CH3) ,I,) ,]-The
First Organometallic
Complexes with direct Co-Sn-Chalcogen
Bonding (Chalcogen = Se, Te)
3
C. Bolm,* A. Gerlach _...._.._....__.
741 -743
>Nq
M a e o b 0 & '
Asymmetric Dihydroxylation with MeOPolyethyleneglycol-Bound Ligands
0
'
\
'/
N
/N
0-DHQD
Ma+-~po+~
'
0
1
K. Benner, P. Kliifers,*
J. Schuhmacher ......_.
.................. 743 - 145
Twenty four hydrogen bonds of the type
R-O-H-.. -0-Si bind the double six-ring silicate
components and the oligosaccharide a-cyclodextrin
(a-CD) in K,,Si,,O,, . 2a-CD.36H20 (1, tetrahedral representation depicted on the right). Thus,
a-cyclodextrin is is incorporated in an unusual way
as a multidentate hydrogen-bond donor capable of
acting as a building block of high information content in a supramolecular assembly. Compound 1 is
of relevance to current discussions on biomineralization.
A Molecular Composite Constructed in
Aqueous Alkaline Solution from a Double
Six-Ring Silicate and a-Cyclodextrin
1
666
8 VCH Verlag.sge.Sellschaft mhH, 0-694551 Weinheim. 1997
0570-083319713607-06663 17.50+ 3 O j O
Angeu. Chem. Inr. Ed. Engl. 1997, 36, No. 7
Threshold levels for the correct theoreticaldescription
of the delocalized [18]annulene (1) have been established with hybrid ab initio density functional computations. Analogous calculations on the bicycloannelated derivative 2 predict a clearly bond-localized structure and earmark this molecule as a new
synthetic target for the study of aromaticity.
0
1
/
/
Contents
K. K. Baldridge, J. S. Siegel* ..... 745-748
Ab Initio Density Functional vs Hartree
Fock Predictions for the Structure of
[I 8lAnnulene: Evidence for Bond Localization and Diminished Ring Currents in
Bicycloannelated [18]Annulenes
U
M. Nendel, K. N. Houk,* L. M. Tolbert,
E. Vogel, H. Jiao,
P. von R. Schleyer* ................... 748-750
An energy increase of only 6 kcalmol-' is associated
with the double-bond localization of the aromatic
syn-bismethano[l4]annulene(1). The correct prediction of aromaticity is surprisingly difficult, as
shown by comparison of several theoretical predictions to experimental results.
The position of the carbohydrate derivative 1 in the
recognition pocket of thrombin has been determined by X-ray structure analysis of the inhibitor/
thrombin complex. This confirms the structural
mimicking of a peptide substrate by 1. The concept
behind the synthesis of this peptidomimetic is based
on attachment of the characteristic functional group
of an amino acid to a carbohydrate backbone.
Nas = naphthylsulfonyl.
1
The Bond Localization Energies in the Aromatic Bismethano[14]annulenes
H. P. Wessel,* D. Banner, K. Gubernator,
K. Hilpert, K. Miiller,
HN
/
&
H
2
T. Tschopp .................................
'
Ho+
OBn
L. Giannini, E. Solari, A. Zanotti-Gerosa,
C. Floriani,* A. Chiesi-Villa,
C. Rizzoli ...................................
753-754
Metal-Metal Multiple Bonds Formed
Across Two Tungsten-Calix[4]arenes by a
Reductive Coupling Reaction
,.
Organocuprates are mostly monomeric in solution!
This is the result of the investigation of the aggregation behavior of reagents with the stoichiometry
[R,Cu(X)Li,], carried out for the first time by
cryoscopy in tetrahydrofuran. Thus, Gilman
cuprates (X = I) and cyanocuprates (X = CN) may
belong to the same structural type 1.
*X.
>I L,
n
g Ceh e~m
~ n t~ d ~.n g 1 1997,
.
36,
No. 7
A. Gerold, J. T. B. H. Jastrzebski,
C. M. P. Kronenburg, N. Krause,*
755-757
G. van Koten* ..........................
R-CU-R
Determination of the Degree of Aggregation of Organocopper Compounds by
Cryoscopy in Tetrahydrofuran
1
+M :4 'N
D.-S. Su, D. Meng, P. Bertinato, A. Balog,
E. J. Sorensen, S. J. Danishefsky,*
Y.-H. Zheng, T.-C. Chou, L. He,
S. B. Horwitz .............................
757-759
I
MeC
0
OH
epothilone €3
~
Carbo-
BNasO
Tungsten-tungsten double and triple bonds are found
in the dimers 1 (structure depicted on the right; calixarene substituents partly omitted) and 2, respectively, formed by the reductive coupling of the corresponding dichlorotungsten compounds. In 1 the two
Na' ions are located in the calixarene cavity; in 2
they bridge the two calixarene units. py = pyridine.
The highest biological activities displayed by
epothilone-related compounds have been found for
epothilone B (1) and a derivative that was prepared
en route to the natural product. Key steps in the
total synthesis were a Suzuki coupling providing a
trisubstituted double bond in the macrocycle and
its subsequent stereoselective epoxidation with
dimethyldioxirane.
6-Guanidinopyranoses : Novel
hydrate-Based Peptidomimetics
751 -752
1
V C H Verlngsgesellschaft m b H , 0.69451 Weinheim, 1Y97
Total Synthesis of (-)-Epothilone B: An
Extension of the Suzuki Coupling Method
and Insights into Structure- Activity Relationships of the Epothilones
0570-0833/97/3607-0667S f7.50+ .50/0
667
Contents
Macrocyclization of 2,3-dicyano-1,4-diox-2-ene
with magnesium propoxide in propanol provided
the enantiomerically pure C,-symmetric (porphyrazinato)magnesium(II) complex 1. The structure of the macrocycle was confirmed by an X-ray
crystallographic study on the demetalated porphyrazine.
A. S. Cook, D. B. G. Williams,
A. J. P. White, D. J. Williams,
S. J. Lange, A. G. M. Barrett,*
B. M. Hoffman* _..._..__...__...__.___.
760-761
Regioregular poly(ferrocenylsi1ane)s 1, end-group-functionalized polymers of controlled molecular weight, and novel graft copolymers 2 are accessible by transitionmetal-catalyzed ring-opening polymerization of strained ferrocenophanes at ambient temperature.
P. Gomez-Elipe, P. M. Macdonald,
I. Manners* ................................
762-764
p-*yq
.$,
4"
M e Me
J=gs%?
&?i
[XfI;
Md:\Me
Enantiomerically Pure "Winged" Spirane
Porphyrazinoctaols
Architectural Control in the TransitionMetal-Catalyzed Ring-Opening Polymerization of Silicon-Bridged [IIFerrocenophanes
2
Me
Trifluoromethylacetalgroups as chiral auxiliaries enhance diastereoselectivity in nucleophilic additions to benzo- and naphthoquinone derivatives. In the methylation
of 1 to give 2 and 3 facial selectivity is induced not by steric effects but by long-range
electrostatic effects. This principle may be used in the design of a new class of chiral
auxiliaries.
4
M:;k.r.
O'.'
+
[0OH
0'"
u
U
F3C"'
F3C"
I
P. Wipf,* J.-K. Jung ......_........... 764-767
Long-Range Electrostatic Effects in Synthesis: Dipole-Controlled Nucleophilic Addition to a Naphthoquinone Acetal in
Model Studies toward Diepoxin o
MG;
0''' 0
F,C"*U
2
3
1.5 : 1 (82%)
The palladium-catalyzed carbocyclization of ally1
carboxylates with alkenes developed by Oppolzer
proceeds smoothly via cationic complexes (depicted
schematically on the right). In contrast, complexes
with two donor phosphane ligands or a bidentate
ligand are not productive intermediates in the
cyclization process.
The lack of suitable crystals has meant that it has not
been possible to carry out a conventional singlecrystal X-ray structure analysis to determine the
structure of red fluorescein. Instead, the application
of a Monte Carlo method has allowed the crystal
structure to be determined directly from powder Xray diffraction data. Importantly, fluorescein was
treated as a nonrigid fragment in the structure solution calculation, illustrating the generalized application of the Monte Carlo method. The molecules
form layers in the crystal (with extensive
C = O - - H - 0 hydrogen bonding), and within each
1
+
B<
E. Gomez-Bengoa, J. M. Cuerva,
A. M. Echavarren,*
G. Martorell ..__..._....
Cationic Intermediates in the Intramolecular Insertion of Alkenes into (q3-Allyl)palladium(I1) Complexes
M. Tremayne, B. M. Kariuki,
K. D. M. Harris* .._...._.._...._..._...
770-772
Structure Determination of a Complex Organic Solid from X-Ray Powder Diffraction Data by a Generalized Monte Carlo
Method: The Crystal Structure of Red
Fluorescein
layer the moIecuIes are stacked in columns (as
shown on the right).
668
0 VCH Verlagsgesellschafi mbH. 0-69451 Weinheim, 1997
0570-0833/97/3607-0668 $17.50+ S O j O
Angew. Chem. Inl. Ed. Engl. 1997,36, No. 7
Two-phase catalysts with sugar-substituted ligands,
such as glycoside-triarylphosphanes 1a-c, reveal
advantages over catalysts with the classical TPPTS
ligands in Heck and Suzuki reactions. A simple and
generally applicable synthesis has been developed
for this new class of neutral, hydrophilic ligands. On
account of thermoreversible solvation, the concentration of the two-phase catalyst in the nonpolar
medium increases with increasing temperature, as
shown by the Nernst distribution coefficient determined for one of the new ligands at different temperatures.
M. Beller,* J. G. E. Krauter,
A. Zapf ...........................................
R’ OH
R z & o e p p b
H
R3
772-714
-
l a Ri
= H, R2 =OH, R3 = NHAc
1b ~1 =OH, ~2 = H, R3 = OH
Ic R1 = H, R2 = OH, R3 = OH
Carbohydrate-Substituted Triarylphosphanes-A
New Class of Ligands for
Two-Phase Catalysis
Polymerization of ethylene is initiated by
[Sm(C,Me,),], an observation that led to a new synthetic route to this Sm”‘ compound. Tetramethylfulvalene proved to be the crucial reagent and was
also used in the synthesis of [U(C5Me5),], the first
tris(pentamethylcyclopentadieny1) complex of an
actinide metal (see structure on right).
W. J. Evans,* K. J. Forrestal,
J. W. Ziller ____...______....________......_
774-776
Calcium ions and organic l i g a n d e i n this case deprotonated erythritol-together are capable of reducing aggregation of oxoiron(n1) species to such an
extent that well-defined oxoclusters can be isolated.
In the title cluster, an Fe,O,, rutile core is extended
by further iron centers to yield a hematite-type microtwin (Fe,,O,,; arrangement of iron centers depicted on the right), which may be related to
metastable oxoiron(II1) phases in terms of structure
and magnetism.
J. Burger, P. Kliifers* ______......____
776-779
Optimizing reactions for one set of conditions, although they normally proceed under
different conditions, is a promising method for the directed development of one-pot
reaction sequences. The validity of such “integrated” chemical processes has been
shown by an extremely concise synthesis of vitamin A, which involves coupling of
two C,, building blocks [Eq. (a)].
A. Orita, Y Yamashita, A. Toh,
J. Otera* ....................................
779-780
A new strategy for solid-phase combinatorial synthesis: Application of laser optical synthesis chips
(shown schematicaIIy on the right; other end groups
include OH, COOH, and C1) and directed sorting
allows formation and reliable characterization of libraries of small organic molecules, peptides, and
oligonucleotides.
Activity of [Sm(C,Me,),] in Ethylene Polymerization and Synthesis of [U(C,Me,),],
the First Tris(pentamethylcyc1opentadienyl) 5f-Element Complex
Stabilization of Iron Clusters by Polyolato
Ligands and Calcium Ions: An Fe,, 0x0cluster from Aqueous Alkaline Solution
Integrated Chemical Process: An Extremely Concise Synthesis of Vitamin A
X.-y. Xiao,* C. Zhao, H. Potash,
M. P. Nova ................................
780-782
Combinatorial Chemistry with Laser Optical Encoding
*Author to whom correspondence should be addressed
6 70
J>
VCH VerogsgeseellschqfimbH, D-6945fWeinheim,1997
OS70-0833/97/3607-0670$ I7.S0+ .SO10
Angen. Chem. In,. Ed. Engl. 1997, 36, NO. 7
BOOKS
Green Chemistry. Designing Chemistry for the Environment
P. T. Anastas, T. C. Williamson
Multiply Bonded Main Group Metals and Metalloids
The Chemistry of Heterocycles
*
*
R. West, F.G. A. Stone
. T. Eicher, S. Hauptmann
German versions of all reviews, communications, and highlights in this issue appear
in the first April issue of Angewandte Chernie. The appropriate page numbers can be
found at the end of each article and are also included in the Author Index on p. 787.
J. 0 .Metzger .....................................
783
784
M . Weidenbruch ......__
_ _ _ _ _ ___._
.........______
7:D.Lash .______..........._..._________.____
785
SERVICES
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Keywords
786
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Author Index
787
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788
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